Facial Feedback on the Perception and Memory for Emotional Faces

Facial Feedback on the Perception and Memory for Emotional Faces | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Facial Feedback on the Perception and Memory for Emotional Faces Ivan Nabil Ras, Monica Bucciarelli, Francesco Ianì, Teresa Limata, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8252710/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract Our investigation explores the facial feedback hypothesis in relation to the perception and memory of emotional faces. In Experiment 1, participants rated the valence of angry, neutral, and happy faces while vertically holding a pen either between their teeth (smile-facilitating condition) or between their lips (smile-inhibiting condition). Results indicated that participants in the teeth condition rated happy faces more positively than participants in the lips condition, while no difference was found for angry and neutral faces. Moreover, reaction times for the evaluation of angry faces were longer than the ones for neutral and happy faces. Experiment 2 assessed long-term memory for angry, neutral, and happy faces. During encoding, participants saw the same faces as in Experiment 1. During recognition, they had to select the previously seen faces from a set containing target and filler faces while holding a pen either between their teeth or their lips. Results indicated no significant differences both for accuracy and recognition times between the two groups. The results revealed better memory performance for angry faces compared to neutral and happy ones, regardless of the pen-in-mouth condition. Taken together, these findings suggest that this procedure influences the perception of happy faces only, while the manipulation had no significant effect on memory. Interestingly, angry faces required more time to be evaluated in Experiment 1 and were recognized more accurately in Experiment 2. facial feedback hypothesis perception memory embodied emotion emotional facial stimuli Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Public Significance Statement The purpose of our study is to increase the understanding of how facilitating/inhibiting smile influences both the perception and the memory of emotional faces. By unobtrusively manipulating the activation/inhibition of the zygomatic muscle (through the “pen-in-mouth procedure”) and by presenting happy, angry, and neutral expressions, our work aims to clarify whether this manipulation can affect how people evaluate (Experiment 1) and remember (Experiment 2) emotional information from human faces. Introduction The Facial Feedback Hypothesis (FFH) posits that facial expressions can influence or even trigger emotional experiences, suggesting a crucial bidirectional relationship between facial muscle activity and emotions (Strack et al., 1988). Moreover, empirical findings suggest a relationship between bodily states and memory, i.e., a congruent posture between encoding and retrieval facilitates recall (e.g., Dijkstra et al., 2007). The aim of the present investigation is to employ the “pen-in-mouth procedure” used by Strack et al. (1988) to test the effects of facial manipulation both on perception and long-term memory for emotional faces. Regarding perception, Strack et al. (1988) found evidence in favor of the FFH: participants rated humorous cartoons more positively when their facial muscle activity was manipulated to facilitate smiling. The aim of Experiment 1 is to replicate the evidence supporting the FFH, by using the same procedure as in Strack et al. (1988) but different stimuli: happy faces instead of funny cartoons. Moreover, Experiment 1 examines the presence or absence of the facial feedback effect when participants evaluate angry faces. With the intent to integrate the FFH with evidence of the congruency effect of bodily states on memory, Experiment 2 explores the potential beneficial effect on long-term memory when the observer’s facial expression and the observed one are congruent. Facial Feedback Hypothesis and Perception The FFH has been widely debated in research concerning the nature of emotions. Although there are several variants of this theory, it is generally based on the idea that muscle feedback from facial expressions plays a causal or at least modulating role in emotional experience. This idea has several historical roots. Charles Darwin stated that “The free expression by outward signs of an emotion intensifies it. [...]. Even the simulation of an emotion tends to arouse it in our minds.” (1872, p. 366). Based on this premise, several researchers emphasized the importance not only of facial expression but more in general of bodily states in determining subjective emotional experiences. One of the most important theories advocating this approach was put forward by James (1884) who argued that emotions are essentially the perception of bodily changes rather than purely mental states: “[…] the more rational statement is that we feel sorry because we cry, angry because we strike, afraid because we tremble, and not that we cry, strike, or tremble, because we are sorry, angry, or fearful […]” (1884, p. 190). According to James, the process of emotional experience starts with an internal or external stimulus that triggers changes in the body’s state at a behavioral, physiological and expressive level. The perception of these changes gives rise to a subjective emotional experience. Emotions are therefore rooted in the body's reactions to stimuli and each emotion is characterized by specific changes in bodily states. Following Darwin and James, Allport (1922) and later Tomkins (1962a, 1962b) emphasized the role of the facial muscles in producing and modulating emotional experience. In particular, Tomkins’ theory highlights the critical role of facial feedback in the subjective experience of emotions, suggesting that an internal or external emotional stimulus triggers an inborn “affect program” (1962a, p. 244) that transmits messages via motor and circulatory pathways to the face; the face then sends sensory feedback to the brain and when this feedback reaches consciousness, it is experienced as a specific emotion. Crucial for this topic, Ekman et al. (1983) showed that performing a directed facial action task, in which participants are instructed to contract specific facial muscles (e.g., for fear: “raise your brows and pull them together”, “now raise your upper eyelids”, “now also stretch your lips horizontally, back toward your ears”, p. 1208), produces different autonomic nervous system reactions for specific emotions and elicits the relative subjective feelings. Although Ekman and colleagues were careful not to mention emotion labels, this methodology has been criticized by Strack et al. (1988) because participants were asked to mimic expressions corresponding to emotions. This could have led to the possibility that their awareness of mimicking emotion expressions induced the emotions rather than the facial feedback conceived as a purely implicit mechanism. Furthermore, participants’ awareness of imitating emotions may have led them to comply with the experimenters’ expectations. To address these potential shortcomings, Strack et al. (1988) tested the FFH with a novel experimental paradigm. Participants were told that the purpose of the study was to investigate the difficulty of performing tasks, such as writing or drawing, while holding a pen in their mouth, as people with a physical disability who cannot use their hands might do. One group held the end of a pen vertically with their teeth (facilitating smile), while the other group held the end of a pen vertically with their lips (inhibiting smile). This methodological approach was used to ensure that any emotional changes observed were due to the induced facial expressions and not to the participants’ awareness of the true aims of the study. While holding the pen, participants rated the funniness of cartoons. The authors hypothesized that holding the pen between the teeth would facilitate a smile and enhance the feeling of happiness, which in turn would lead to a more positive evaluation of the cartoons. The results confirmed the hypothesis, showing that participants in the teeth condition rated the cartoons as funnier than those in the lips condition. This study is considered revolutionary due to the introduction of the “pen-in-mouth procedure”: by facilitating or inhibiting a smile without explicit instructions, the authors addressed the criticism of demand characteristics and provided stronger evidence for the FFH. Nevertheless, various attempts to replicate these findings have produced controversial results (Coles et al., 2019). To clarify this issue, Wagenmakers et al. (2016) conducted a registered replication study involving 17 independent research groups that attempted to replicate the original study of Strack et al. (1988). Overall, the results showed no significant difference in funniness ratings between the teeth and lips conditions: out of 34 Bayesian analyses (two analyses for each replication attempt), only one provided evidence in favor of the alternative hypothesis. Noah et al. (2018; see also Strack, 2016) hypothesized that the failure to replicate the original study may be related to a critical procedural difference: in the replication study, but not in the original one, participants were aware that they were being videotaped. The authors tested this hypothesis by creating two experimental conditions, one characterized by the presence of a camera and the other by its absence. The results supported their hypothesis: the facial feedback effect was significant without a camera, but not when a camera was present. This suggests that awareness of being observed can negatively influence the facial feedback effect. The findings of Noah et al. (2018) are further supported by Marsh et al. (2019), who conducted a study involving undergraduate students exposed to the “pen-in-mouth procedure” while evaluating the funniness of cartoons without being video recorded. The authors found a significant difference in humor ratings between the two experimental conditions: cartoons rated while participants held the pen with the teeth were consistently evaluated as funnier than those rated while holding the pen with the lips. The results replicated the effect reported by Strack et al. (1988) and provided further evidence in favor of the FFH. Other studies investigated the FFH with the pen-in-mouth procedure, but also with other facial manipulations. We will discuss their results in relation to the ones of the present study in the General Discussion. Facial Feedback Hypothesis and Long-Term Memory The encoding specificity principle states that it is easier to retrieve a memory when contextual elements present at encoding match those present during retrieval (Tulving & Thomson, 1973). Moreover, research has shown that memory retrieval involves sensorimotor pathways that simulate events occurred during encoding (for a review see Ianì, 2019). Thus, understanding how bodily states influence memory is crucial. Dijkstra et al. (2007) investigated the effect of posture congruency at encoding and recall. The authors hypothesized that assuming a posture congruent between encoding and retrieval facilitates recall. To test this hypothesis, participants were asked to recall autobiographical memories of specific events (e.g., the last dental visit) while taking postures that could be either congruent (i.e., lying on a recliner with their mouth open) or incongruent (i.e., standing upright with their hands on their hips). The results showed that participants recalled past experiences faster when assuming a congruent posture compared to an incongruent posture, both in the immediate and in the delayed recall test (two weeks later). Another study by Limata et al. (2021) addressed this topic by asking participants to perform actions on objects while standing or sitting at encoding. During the recall of the previously performed simple hands’ actions, half of the participants were standing, the other half were sitting. Contrary to the hypothesis, congruent postures during encoding and retrieval did not improve accuracy, suggesting that posture, understood as a simple static position of the body, has no influence on the retrieval process of the actions performed by participants. Conversely, Limata et al. (2023) have shown that body posture can influence memory in a recognition task when the posture is manipulated in a way that is crucial for the execution (and the potential execution) of actions. During encoding, participants observed a series of objects and performed actions on another series of objects using upper limbs. During recognition, participants of one group held their hands in front of them (non-interfering posture), and participants of a second group behind their back (interfering posture). Participants with a non-interfering posture recognized enacted objects faster than observed ones, but this advantage vanished for the interfering posture group. This indicates that an inconsistent posture with the encoding action affects memory in terms of reaction times. Despite the evidence for the relationship between bodily states and memory (Ianì, 2019), there is a notable lack of research on how facial muscle manipulation through the “pen-in-mouth procedure” can affect memory. To our knowledge, there is only one study addressing this topic: Kuehne et al. (2021) attempted to investigate in what ways the manipulation of facial feedback by induced smiling influences the immediate recall of emotional facial expressions. In this study participants were asked to carry out a working memory task on happy and sad faces while holding a pen between their teeth (facilitating smile) or with their non-dominant hand. More specifically, the participants were presented with happy or sad faces of varying intensities during encoding. After each target face, a neutral face was presented and participants had to reproduce the target facial expression by scrolling the mouse wheel: by scrolling up, participants could assign different intensities of happiness to the neutral face; by scrolling down, they could assign different intensities of sadness. The results showed that the participants in the teeth condition reproduced happy faces with higher accuracy. This shows how the facilitation of smiling selectively improves the immediate memory of happy faces. Overview of the Present Study We conducted two experiments by using the “pen-in-mouth procedure” as in Strack et al. (1988) to test the FFH on the perception of emotional faces (Experiment 1) and the memory of emotional faces (Experiment 2). We used the “pen-in-mouth procedure” to shed light on the controversial results obtained through this manipulation. Moreover, this procedure appears to be the best way to limit participants’ awareness of the true aim of the experimental conditions (smile facilitation vs inhibition, Coles et al. 2022). In Experiment 1 we used the “pen-in-mouth procedure” to test whether the participants’ own facial expression influences their evaluation in terms of valence of angry, neutral, and happy faces. Crucially, our experimental manipulation includes angry faces, whereas Strack et al. (1988) only used positively connoted stimuli (humorous cartoons). Experiment 2 investigates the relationship between the facial muscles’ activity manipulated by the “pen-in-mouth procedure” and long-term memory for angry, neutral, and happy faces. The same kind of stimuli (angry, neutral, and happy faces from the KDEF, Karolinska Directed Emotional Faces, Lundqvist et al., 1998) were used in the two experiments. Both experiments were approved by the Bioethical Committee of the University of Turin. For each experiment we report how we determined our sample size, all data exclusions, all manipulations and all measures. Table S1 in the Supplementary Materials reports the allocation of men and women to the groups (teeth vs lips) for the two experiments. Experiment 1: Do Observers’ Facial Expressions Modulate the Perception of Observed Angry, Neutral and Happy Faces? Experiment 1 focuses on the role that the observer’s facial expression plays in modulating the valence evaluation of angry, neutral, and happy faces. Based on Strack et al. (1988), we hypothesised that when the observer’s muscle activity associated with smiling is facilitated, happy faces should be rated more positively than when it is inhibited. If this prediction holds, the results will provide support for the FFH regarding emotional expression perception. With respect to angry and neutral faces, we do not have specific predictions: to our knowledge, most of the studies on perception employing the “pen-in-mouth procedure” focused exclusively on positively connoted stimuli. Soussignan (2002) conducted the only study that employed this procedure with participants rating their reaction to both positive and negative emotionally connoted stimuli (i.e., videoclips). The author replicated Strack et al.’s (1988) results with higher positive reactions for positively connoted stimuli when smiling was facilitated. No significant difference was detected in the reactions to negative stimuli, regardless of the position of the pen. The participants’ task was to rate the emotional valence of angry, neutral, and happy faces on a 7-point Likert scale, ranging from extremely negative to extremely positive. Half of the participants held the pen between their lips, a pose that inhibits smiling, and the other half held the pen between their teeth, a pose that facilitates smiling. Method Participants To determine the required sample size, an a priori power analysis based on an effect size of d = 0.66 derived from a similar study (Soussignan, 2002) was conducted using G*Power (Version 3.1.9.7; Faul et al., 2007). Since we had a specific hypothesis only for happy faces, we ran a power analysis for a one-tailed independent-samples t test assessing the difference in ratings for happy faces between two groups (teeth vs lips). The significance level was set at α = .05, with desired power (1 – β) = .80. The results indicated that a total sample size of 60 participants (30 per group) would be sufficient to detect the expected effect. The 61 participants (26 men, 35 women, mean age = 24.21 years, SD = 4.52) were students at the University of Turin. Data from one participant was excluded from the analyses because instead of holding firmly the pen between her lips she let it slide down and played with it. Therefore, the final sample was composed of 60 participants (26 men, 34 women, mean age = 24.28 years, SD = 4.52). All participants were Italian, a minority of them ( n = 3) had foreign origins but were grown in Italy and were fluently speaking Italian. Because the FFH is discussed in many psychology classes, we recruited participants from other university courses. They voluntarily participated in the experiment in exchange for academic credit. Materials The material consisted of 18 faces of 18 different actors selected from the KDEF database (Lundqvist et al., 1998), with 6 faces belonging to each of the following categories: angry, neutral, happy. The faces in each category belong to 3 women and 3 men. We used a 7-point Likert scale ranging from 0 ( extremely negative ) to 6 ( extremely positive ), with intermediate values of 1 ( negative , 2 ( slightly negative ), 3 ( neutral ), 4 ( slightly positive ), 5 ( positive ), to assess the emotional valence participants assigned to each stimulus. To calculate response times, the Likert scale was structured in a semicircular shape with the mouse automatically positioned equidistantly from each label. Procedure The experiment was conducted in a single, individual session in a quiet room. Participants were randomly assigned to two experimental groups: in the TEETH group they were invited to vertically hold a pen between the teeth (facilitating smile), and in the LIPS group they were invited to vertically hold a pen between the lips (inhibiting smile) (see Figure 1 in Strack et al. 1988, p. 771). During the experimental session, participants were video recorded with a hidden mini camera to control whether they held the pen correctly. We made sure that they were not aware of being video recorded to avoid the inhibiting effect on the facial feedback observed in Noah et al. (2018). At arrival the experimenter asked the participant to sign the informed consent and then to sit in front of a computer to read with the experimenter the following instructions on the computer screen: Thank you for taking part in this study. You will see a series of photos showing faces. For each photo, you have the task of judging the extent to which the emotion expressed by the person is negative or positive.Shortly after each photo, a scale appears on which you can give your rating from “extremely negative” to “extremely positive”. You must use the mouse to enter your rating. We ask you not to let go of the mouse until the end of the experimental session. The scale is the following: Try to answer spontaneously without thinking too much about it. Press the space bar for further instructions. We also ask you [to hold this pen between your teeth without touching it with your lips/to hold this pen between your lips without touching it with your teeth] for the whole duration of the experimental session. Before you start, we ask you to place the mouse in a position that is comfortable for you. Once the experimental session is finished, we ask you to knock on the door of the room. Press the space bar when you want to start. After reading the instructions, right before the beginning of the task, the experimenter made sure that the participant was holding the pen correctly between the teeth or lips and left the room. Each participant was shown a total of 18 faces. Each face was presented for 5 seconds and immediately afterwards the 7-point Likert scale appeared on the screen on which the participants were asked to rate the emotional valence of the face they had just seen. After the rating, a new face appeared on the computer screen. The stimuli were presented on the computer screen with E-Prime 3.0 (Psychology Software Tools, 2020). They appeared in random order with the only constraint that two faces of the same valence were not presented consecutively. We recorded the emotional valence ratings of each face and the relative reaction times. At the end of the experimental session, participants were asked to read and sign the post-study consent form. They were informed they had been videotaped (none of them noticed the hidden camera) and asked again whether they consent or not to the use of their data and the video recording. After the experimenter had obtained consent for this use, participants were informed of the aims of the study. Results 1 Figure 1 shows the participants’ mean ratings for the facial expressions on the emotional valence scale in the two experimental conditions: pen between the teeth and pen between the lips. Exact means and standard deviations are provided in Table S2 in the Supplementary materials. Figure 1 Means and Standard Deviations for Participants’ Valence Ratings as a Function of the Type of Stimuli and Experimental Groups (Teeth vs Lips) in Experiment 1 Since ordinal data can be treated as continuous (Robitzsch, 2020), we considered valence ratings as a continuous variable to ensure methodological consistency with the analyses of Experiment 2. A 2 (GROUP: Teeth, Lips) x 3 (EMOTION: Angry, Happy, Neutral) mixed ANOVA was conducted on the rating scores. Mauchly’s test indicated that the assumption of sphericity was violated for the Emotion within-subjects variable, χ²(2) = 11.56, p = .003; therefore, Huynh–Feldt–corrected degrees of freedom are reported. There was a significant main effect of EMOTION ( F (1.77, 102.37) = 967.58, p < .001, ηp² = .943), while the main effect of GROUP was not significant ( F (1, 58) = 0.09, p = .768, ηp² = .002). This shows how, regardless of the pen manipulation, neutral faces were rated more positively than angry ones and happy faces were rated more positively than neutral ones. Crucially, the EMOTION by GROUP interaction was statistically significant ( F (1.77, 102.37) = 3.28, p = .048, ηp² = .054). To follow up this interaction, independent samples t-tests were conducted for each emotional condition. For happy stimuli, ratings were significantly higher in the teeth group compared to the lips group ( t (58) = 2.75, p = .008, d = 0.71, mean difference = 0.26, 95% CI [0.07, 0.44]). For angry stimuli the comparison between teeth and lips was not significant ( t (58) = 1.25, p = .218). Levene’s test suggested unequal variances ( F (1, 58) = 4.67, p = .035); however, the adjusted test with corrected degrees of freedom led to the same conclusion ( t (45.41) = –1.25, two tailed p = .219 d = 0.32, mean difference = –0.22, 95% CI [-0.57, 0.13]). For neutral stimuli no significant difference was found between groups ( t (58) = −0.97, two tailed p = .336, d = 0.25, mean difference = -0.09, 95% CI [-0.29, 0.10]). Taken together, these results indicate that, although the groups did not differ in overall rating levels, they differed specifically in their evaluations of happy faces, with the teeth group giving significantly more positive ratings than the lips group. Figure 2 shows the response times of the participants when evaluating the emotional valence of the faces in the two experimental conditions: pen between the teeth and pen between the lips. Exact means and standard deviations are provided in Table S3 in the Supplementary materials. Figure 2 Mean Response Times (in Milliseconds) and SDs for Participants’ Ratings as a Function of the Expressed Emotion and Experimental Groups (Teeth vs Lips) in Experiment 1 A 2 (GROUP: Teeth, Lips) x 3 (EMOTION: Angry, Happy, Neutral) mixed repeated-measures ANOVA was conducted on Reaction Times. Because Mauchly’s test indicated a violation of sphericity, the Huynh–Feldt correction was applied to the within-subjects factor. There was a significant main effect of EMOTION ( F (1.91, 110.90) = 22.60, p < .001, ηp² = .280), indicating that participants’ response times differed across the three emotional conditions. Bonferroni-adjusted pairwise comparisons showed that angry faces elicited significantly slower responses than both the happy ( p < .001, mean difference = 635.33, 95% CI [367.97, 902.70]) and neutral ones ( p < .001, mean difference = 664.81, 95% CI [351.49, 978.13]). No significant difference emerged between the happy and neutral faces ( p = 1.000, mean difference = 29.48). No main effect of GROUP was found ( F (1, 58) = 0.063, p = .803, ηp² = .001). There was no interaction effect between EMOTION and GROUP ( F (1.91, 110.90) = 0.094, p = .91, ηp² = .002). Overall, the results show that, in line with the FFH, happy faces were rated more positively when the activation of the zygomatic muscle was facilitated. This finding is consistent with Strack et al. (1988), where positive stimuli (funny cartoons) were rated more positively in the teeth condition than in the lips condition. Our results also show longer reaction times when evaluating angry faces compared to happy and neutral faces. This may be because negative stimuli require longer cognitive processing than positive or neutral stimuli due to the threatening values they may carry (Baumeister et al., 2001). Experiment 2: Do Observers’ Facial Expressions Modulate Long-Memory of Observed Angry, Neutral and Happy Faces? The aim of Experiment 2 was to investigate whether the observer’s facial expressions modulate the memory of previously seen emotional faces. Using the same facial manipulation as in Experiment 1, we tested whether congruency between the observer’s facial expression and the emotion conveyed by the observed face favors recognition. The experiment consisted of two phases. In the encoding phase, participants observed 24 stimuli, equally divided into 8 angry, 8 neutral, and 8 happy faces. To ensure they processed the emotional expression, participants were asked to rate the positive or negative emotional state of the person depicted in each photo. In the recognition phase, participants encountered 24 screens, each depicting the same actor with an angry, happy, and neutral face. For each actor, only one of the three facial expressions had been shown during encoding. The participant’s task was to identify this expression while going through the “pen-in-mouth procedure”. Method Participants A power analysis revealed that at least 24 participants were required to reach an appropriate statistical power of 0.95 to detect a significant effect (with α = 0.05), assuming a medium effect size ( f = 0.35, η p 2 =0.109), the same found by Kuehne et al. (2021), who conducted a similar study on the effect of facial expression manipulations on immediate recall. The sample size was determined using the G-Power software (Version 3.1.9.6; Faul et al., 2007). To recruit participants, we offered students from the University of Turin the opportunity to earn credits. The participants had not taken part in Experiment 1. All participants were Italian. For the same reasons discussed in Experiment 1, we recruited students not attending a psychology course. We tested a total of 28 participants but data from 2 participants was removed from the analyses: one participant was aware of the FFH and the “pen-in-mouth procedure”, while a second participant encountered a technical problem (blocking of the response keys) during the experiment. Thus, the final sample consisted of 26 participants (14 men, 12 women, mean age = 24.41 years, SD = 4.31). Materials The material consisted of the 72 pictures of 24 different actors from the KDEF database (Lundqvist et al., 1998). Each actor was represented in three photos with 3 different facial expressions (angry, happy, neutral). Procedure The experiment was conducted in a single, individual session in a quiet room. As in Experiment 1, participants were randomly assigned to the LIPS or the TEETH condition. For both groups, the experiment consisted of two phases, encoding and recognition, interrupted by a distractor task At their arrival participants were asked to read and sign the informed consent form. Then they were asked to sit in front of a computer to begin the encoding phase. The following instructions were read by the participant together with the experimenter: Thank you for your participation. You will be presented with photos of faces and your task is to rate how negative or positive the emotion expressed by the person is. Immediately after each photo is presented, a scale appears that allows you to rate it from extremely negative to extremely positive. Please use the mouse to express your evaluation. Try to answer spontaneously without thinking too much about it. Press the space bar when you want to start. During the encoding phase, each participant was presented with 24 faces for 5 seconds each. Immediately after the presentation of each face, the same 7-point Likert scale used in Experiment 1 appeared on the screen, on which the participants rated the emotional valence of the face they had just observed. The ratings obtained were not considered a dependent variable and had only the goal of ensuring that the participants’ attentive resources were directed towards the stimuli. After completing the encoding phase, each participant performed a ten-minute distractor task consisting in finding differences between pairs of vignettes. No faces or emotions were shown in these cartoons to avoid interference with the experimental material. Then the experimenter entered the room and instructed the participant for the recognition phase. The instructions for the recognition task were the following: In this phase you will see a series of screens, each composed of three photos of the same actor. In each screen, one of the three photos has already been presented to you in the previous phase: your task is to identify it. To answer, press the left arrow to indicate the photo shown on the left, the down arrow to indicate the central image, the right arrow to indicate the photo shown on the right of the screen. We ask you to give the answer as soon as you are sure by pressing the corresponding key. For the duration of the experiment, keep the fingers of one hand resting on the labeled keys. We also ask you [to hold this pen between your teeth/lips without touching it with your lips/teeth]. Press the space bar when you want to start. After reading the instructions and before leaving the room, the experimenter made sure that the participant was holding the pen correctly between the teeth or lips. During this phase, participants in both groups were presented with 24 screens, each displaying three photographs of the same actor: one with an angry expression, one with a neutral expression, and one with a happy expression (see Fig. 3). For each displayed screen, only one of the three photographs was shown during encoding. The participant’s task was to identify the previously seen photo by pressing one of the three QWERTY-keyboard keys V, B, N, respectively labeled with a left, down, or right arrow. To permit an accurate measurement of reaction times, participants were instructed to keep three fingers of the same hand resting on the response keys throughout the whole recognition phase. The stimuli were presented on the computer screen with E-Prime 3.0 (Psychology Software Tools, 2020). We recorded the recognition accuracy and the reaction times for each displayed screen. The order of presentation of the different actors was randomized as well as the position of the different emotional expressions. In this phase, the participants were video recorded with a hidden mini camera. The purpose of the video recording was to ensure that the pen was well positioned and that the participant kept three fingers of the same hand resting on the answer keys for the entire duration of the task. After completing the recognition task, the experimenter asked the participant to read and sign the post-test consent form where they were informed that they had been videotaped. After obtaining consent for this use, the experimenter shared with each participant the aims of the study and asked if they had noticed that they had been video recorded (none of them noticed the hidden camera) and if they had any previous knowledge about the FFH or the pen-in-mouth procedure. Results Figure 4 shows the participants’ mean accuracy rates in discriminating seen and unseen faces as a function of the displayed EMOTION (Angry, Neutral, Happy) and of the GROUP (Teeth vs Lips). Exact means and standard deviations are provided in Table S4 in the Supplementary materials. A 2 (GROUP: Teeth, Lips) x 3 (EMOTION: Angry, Happy, Neutral) mixed ANOVA was conducted to examine the effects of facial manipulation and emotional facial expressions on accuracy. The main effect of EMOTION was significant ( F (2, 48) = 6.72, p = .003, ηₚ² = .219). A post-hoc comparison with Bonferroni correction revealed that angry faces were recognized more accurately than happy ( p = .014, mean difference = 0.10, CI [0.02, 0.18]) and neutral ( p = .005, mean difference = 0.11, CI [0.03, 0.19]) faces. No difference was found between happy and neutral faces ( p = 1.00, mean difference = 0.01, CI [-0.09, 0.10]). The main effect of GROUP was not significant ( F (1, 24) = 1.49, p = .234, ηₚ² = .058). The interaction between EMOTION and GROUP was not significant ( F (2, 48) = 0.12, p = .884, ηₚ² = .005). Figure 5 shows the mean response times in discriminating seen and unseen faces as a function of the emotion they expressed and of the participants’ posture. Exact means and standard deviations are provided in Table S5 in the Supplementary materials. A 2 (GROUP: Teeth, Lips) x 3 (EMOTION: Angry, Happy, Neutral) mixed ANOVA was conducted to examine the effects of facial manipulation and emotional facial expressions on reaction times. There was no significant main effect of EMOTION ( F (2, 24) = 1.62, p = .209, ηₚ² = .063). There was no significant main effect of GROUP ( F (1, 24) = 2.29, p = .143, ηₚ² = .087). The interaction between EMOTION and GROUP was also not significant ( F (2, 24) = 1.26, p = .293, ηₚ² = .050). Overall, there was no effect of facial feedback on long-term memory for emotional faces. Furthermore, the results show that angry faces were better recognized in the long-term memory task than neutral and happy faces. This advantage for angry facial expressions may be explained by their greater evolutionary relevance: threatening stimuli tend to capture attention more strongly (as shown by the longer reaction times for angry faces in Experiment 1) and to be encoded more deeply in memory. This is consistent with Kensinger (2007), who showed that the valence of a memory influences recall accuracy, with negative memories remembered in greater detail than positive ones. Similarly, our results suggest that negative emotional stimuli, such as angry faces, may enhance long-term memory retention due to their intrinsic evolutionary significance as a sign of potential threat. General Discussion The present study examined the role of facial feedback in the perception and memory of emotions by employing the “pen-in-mouth procedure” across two experiments, using different emotional facial expressions (angry, neutral, and happy faces) as stimuli. Experiment 1 demonstrated that inducing participants to hold a smile-facilitating posture (pen between teeth) affected their emotional perception, leading them to rate happy faces more positively than those with a smile-inhibiting posture (pen between lips). There was no significant difference between the teeth and lips conditions for neutral and angry faces. The results concerning happy faces are consistent with Strack et al. (1988), who observed that funny cartoons were rated more positively in the smile-facilitating condition than in the smile-inhibiting condition. Experiment 2 revealed no significant effect of participants’ facial posture on recognition accuracy for previously seen emotional faces, suggesting that the influence of facial feedback may be limited to the perceptual domain rather than memory processes. This does not align with previous studies showing that posture can influence memory in recall or recognition tasks (Dijkstra et al., 2007; Limata et al., 2023). The results of Experiment 2 may be explained by two key differences from these studies. First, Experiment 2 examined the effects of congruency between the expression in the stimuli and the participants’ expression, rather than the effects of body congruency between encoding and recognition. Secondly, it examined long-term memory for facial expressions, a type of stimulus not used in other studies on the relationship between bodily states and memory. Interestingly, Experiment 2 revealed that, regardless of the facial manipulation, angry faces are recognized more accurately than neutral and happy faces, while Experiment 1 showed that angry faces require more attentional resources to be evaluated. This is consistent with studies suggesting that our cognitive resources are biased towards prioritizing the recognition of potentially harmful stimuli (Barros et al., 2023). Taken together, these results support the idea that threatening stimuli are intrinsically more relevant due to their importance for survival (Baumeister et al., 2001; Kensinger, 2007). The results of the two experiments indicate that manipulating facial muscles using the “pen-in-mouth procedure” influences perception, but not long-term memory for emotional faces. As other studies have used different facial manipulations to investigate the FFH, it is not easy to compare their results with the present findings. For example, Coles et al. (2019) conducted a meta-analysis and, by considering 286 effect sizes from 138 studies, found a significant, though small, overall effect of facial feedback on subjective emotional experience. However, the studies included in this meta-analysis also used facial manipulations that differ from the “pen-in-mouth procedure”, such as facial mimicry and the directed facial action task. Given the contrast between the failed replication by Wagenmakers et al. (2016) and the results of Coles et al. (2019) providing evidence in favor of the FFH, Coles et al. (2022) conducted a further multi-lab test involving 26 laboratories and 3,878 participants from 19 countries. Participants rated either positive or neutral pictures while holding either a neutral or a happy facial expression. To elicit a happy expression, each participant completed the task in one of three conditions: (a) mimicry of images of actors displaying happiness, (b) voluntary facial action task, or (c) “pen-in-mouth procedure”. The authors found a clear facial feedback effect when facial mimicry and the voluntary facial action task were used, while the “pen-in-mouth procedure” produced less conclusive evidence. Nonetheless, when some participants’ inclusion criteria were relaxed (e.g., performing the task on a device other than a laptop or personal computer), the analysis provided strong support for the facial feedback effect in the pen-in-mouth task as well. It should be highlighted that participants were significantly less aware of the study purposes in the pen-in-mouth condition compared to the two other facial manipulation conditions. Other researchers used the same stimuli as in our study (emotional facial expressions), but the facial manipulations differed. For example, in a study by Blaesi and Wilson (2010), participants viewed 11 randomized photos of the same face on a continuum from smiling to frowning. For each photo, participants were asked to say whether the face was happy or sad. Each participant viewed the stimuli under two conditions. In the Pen condition, they were instructed to hold a pen horizontally (rather than vertically as in Strack et al., 1988) with their teeth, without touching it with their lips. This manipulation was intended to favor a smile. In the No Pen condition, participants received no special instructions. For each participant, the percentage of “happy” responses for each of the 11 stimuli was determined separately for the two conditions. The threshold for perceiving the face as happy was defined as 50% “happy” responses. For each participant, the thresholds for the conditions with and without the pen were compared, showing a lower threshold to perceive a happy expression in the Pen condition. According to the authors, this study shows how simulating a slight smile lowers the recognition threshold for happy faces. Similar results were found by Marmolejo-Ramos et al. (2020, Experiment 1, but see also Marmolejo-Ramos & Dunn, 2013, Experiments 5 and 6). In another study by Oberman et al. (2007, Experiment 2), participants completed four within-subject blocks, each consisting of a series of photos of happy, sad, fearful, or disgusted faces morphed to produce seven levels of intensity. They completed the four blocks under the following conditions: bite (holding a pen horizontally by exerting continuous pressure with the teeth), gum (chewing), lips (holding a pen horizontally with the lips), and rest (baseline). The authors intended the “lips” and “rest” manipulations as control conditions, while the “bite” and “gum” conditions were designed to create irrelevant muscular noise that blocks facial mimicry. On each trial, participants were shown a face and asked to rate the facial expression as conveying happiness, sadness, fear, or disgust. The results showed that the “bite” condition specifically impairs the ability to recognize happy faces and, to some extent, disgusted faces. According to the authors, this can be explained by the mimicry-blocking effect of the “bite” condition. Ponari et al. (2012, Experiment 1) explored the effects of interfering muscle contractions of the top- or bottom-half of participants’ face on the ability to recognize fear, happiness, anger, disgust, sadness, and surprise expressions. They hypothesized that if facial manipulation is causally involved in emotion recognition, then an interfering contraction of face muscles involved in the production of a certain expression should impair the recognition of the very same expression. Participants were assigned to one of the following experimental conditions: (a) active contraction of the muscles in the lower part of their face (“lower” manipulation), i.e. placing a Chinese chopstick horizontally in the mouth while exerting constant pressure with the teeth without the lips touching the chopstick; (b) active contraction of the muscles in the upper part of the face (“upper” manipulation), i.e. to draw together two small round stickers placed near the inner edge of the eyebrows; (c) no muscle contraction (control condition). Participants’ task was to identify the emotion conveyed by a face displayed on a computer screen. The results showed that the lower manipulation impaired the ability to recognize happiness and disgust, the upper manipulation impaired the recognition of anger, while both manipulations reduced the recognition of fear. Interestingly, the above studies that used emotional faces as stimuli employed a different version of the “pen-in-mouth procedure” from that of Strack et al. (1988): participants had to hold a pen/chopstick horizontally (not vertically) between their teeth. Furthermore, the authors’ intention in using this facial manipulation were very different: while Blaesi and Wilson (2010) aimed to create a smile-facilitating condition, Oberman et al. (2007) and Ponari et al. (2012) respectively aimed to create irrelevant muscular noise that blocks facial mimicry or interferes with muscle contractions of the bottom-half of participants’ face. To sum up, studies in literature not only used different methods to test the FFH, but also when they employed the “pen-in-mouth procedure” they used a different variant (e.g., holding the pen horizontally vs vertically). In some cases, even when the variant was the same, the intents differed (e.g., inducing smile vs muscular noise). The lack of consistency in both methodology and intents may have contributed to the controversial results on the FFH. Limitations Due to the difficulties in conducting power analyses for mixed-effects models, in both experiments we used repeated-measures ANOVA and by doing so, we considered an ordinal variable (valence ratings in Experiment 1) as continuous. While our approach is widely used (Robitzsch, 2020), it represents a limitation because it does not fully account for the variability explained by random factors. Moreover, the generalizability of findings in emotional research is often constrained by cultural differences. Mesquita and Frijda (1992) highlight how emotional evaluations are shaped by culture, suggesting that results from one cultural group may not apply universally. Our study, conducted exclusively with W.E.I.R.D. (Western, Educated, Industrialized, Rich, and Democratic) students, reflects this limitation. Future research should account for cultural and socio-economical variability to ensure broader applicability of findings. Conclusions and Future Research Our findings contribute to a deeper understanding of the FFH by delineating its boundary conditions across different domains. Experiment 1 detected no significant difference between the teeth and lips conditions for neutral and angry faces. These findings suggest that manipulating smiles using the “pen-in-the-mouth procedure” affects the evaluation of happy faces, but not neutral or angry ones. Experiment 2 revealed no significant effect of facial muscle manipulation. Taken together, the results of our two experiments suggest that although facial feedback can influence immediate perceptual judgments of emotional expressions, it does not appear to play a role in long-term memory processes. These differences may reflect the fact that the perceptual and memory-related functions of emotional feedback engage different neural circuits and processes. For example, the perception of facial expressions may engage the mirror systems involved in immediate emotional understanding (Tramacere & Ferrari, 2016), whereas memory for facial expressions may rely more heavily on the hippocampal and prefrontal pathways (Sergerie et al., 2005), which may not be directly modulated by facial muscle activity. To summarize, our findings suggest that facial muscle activity plays an important role in modulating the perception of emotional expressions. However, the influence of facial feedback on long-term memory is not clear, suggesting that perceptual and memory processes may rely on facial muscle feedback in different ways. This research highlights the need for further investigation into the effects of facial feedback in different cognitive domains and emphasizes the complexity of theories of embodied emotion (Barsalou, 2008). Of interest for future research could be to further investigate the effect we found in Experiment 1 and to assess both the objective valence and the subjective feeling elicited by emotional faces. Practical Implications The relevance of the proposed study is based on its potential impact on social interaction. Several studies show indeed that facial mimicry can enhance affiliation, pro-social behavior and empathy (e.g., Hess, 2021; Lakin & Chartrand, 2003). This could be particularly relevant in psychotherapeutic settings. In these contexts, the awareness that one’s own facial expression modulates the perception of the faces of others and the emotions expressed by them can be the subject of examination and reflection in the therapist/patient dyad. Regarding memory, our experiments didn’t reveal significant effects. Further research could explore the relationship between facial expressions and memory, offering insight into the field of eyewitness psychology. Declarations Conflict of Interest Statement The authors report there are no competing interests to declare. Funding This work was supported by the Italian Ministry of Education, University and Research, through Research Grant No. 20225ECXPP (to M.B., F.I, C.T. & S.S.) to study the impact of movement, action, and touch on memory. Author Contribution Conceptualization – Development of the main research ideas and overall study goals: S.S and C.T.Data curation – Management, cleaning, and annotation of the dataset: I.N.R.Formal analysis – Application of statistical and analytical techniques for data analysis: F.I. and I.N.R.Funding acquisition – Securing financial support for the project: M.B.Investigation – Execution of the research procedures, including data collection and experimental work: I.N.R. and A.S. Methodology – Development and refinement of the study’s methodological approach and models: F.I. and T.L.Software – Programming, implementation, and testing of software and algorithms used in the study: T.L. and I.N.R.Supervision – Oversight of the research process, including guidance and mentorship: M.B. and S.S.Validation – Verification of analyses, replication checks, and confirmation of findings: S.S., F.I. and I.N.R.Visualization – Preparation and presentation of figures and other visual materials: I.N.R.Writing – original draft – Writing of the initial manuscript draft: S.S. and I.N.R.Writing – review and editing – Critical revision and editing of the manuscript throughout all stages: S.S., I.N.R., F.I., M.B., T.L., A.S. and C.T. Acknowledgement We thank the following students for their help during the experimental sessions: Mariangela De Angelis, Aliona Birda, Gaetano Manica, Constanza Martin, and all the participants. Data Availability The data reported in this paper are archived at the following link: https://h7.cl/1ftCo Author Notes The data reported in this paper are archived at the following link: https://h7.cl/1ftCo Correspondence to this article should be addressed to Susanna Schmidt, Università degli Studi di Torino, Dipartimento di Psicologia, Via Verdi, 10, 10124 Turin, Italy. Email: [email protected] References Allport, F. H. (1922). A physiological-genetic theory of feeling and emotion. Psychological Review, 29 (2), 132–139. https://doi.org/10.1037/h0075652 Barros, F., Soares, S.C, Rocha, M., Bem-Haja, P., Silva, S., & Lundqvist, D. (2023). The angry versus happy recognition advantage: the role of emotional and physical properties. Psychological Research, 87 (1):108-123. doi: 10.1007/s00426-022-01648-0. Barsalou, L. W. (2008). Grounded cognition. Annual Review of Psychology , 59 (1), 617-645. https://doi.org/10.1146/annurev.psych.59.103006.093639 Baumeister, R. 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Inhibiting and facilitating conditions of the human smile: A nonobtrusive test of the facial feedback hypothesis. Journal of Personality and Social Psychology, 54 (5), 768–777. https://doi.org/10.1037/0022-3514.54.5.768 Soussignan, R. (2002). Duchenne smile, emotional experience, and autonomic reactivity: A test of the facial feedback hypothesis. Emotion, 2 (1), 52–74. https://doi.org/10.1037/1528-3542.2.1.52 Tomkins, S. S. (1962a). Affect, imagery and consciousness: Vol. 1. The positive affects. Springer. Tomkins, S. S. (1962b). Affect, imagery and consciousness: Vol. 2. The negative affects. Springer. Tramacere, A., & Ferrari, P. F. (2016). Faces in the mirror, from the neuroscience of mimicry to the emergence of mentalizing. Journal of Anthropological Sciences , 94 , 113–126. https://doi.org/10.4436/JASS.94037 Tulving, E., & Thomson, D. M. (1973). Encoding specificity and retrieval processes in episodic memory. Psychological Review, 80 (5), 352–373. https://doi.org/10.1037/h0020071 Wagenmakers, E.-J., Beek, T., Dijkhoff, L., Gronau, Q. F., Acosta, A., Adams, R. B., Albohn, D. N., Allard, E. S., Benning, S. D., Blouin-Hudon, E.-M., Bulnes, L. C., Caldwell, T. L., Calin-Jageman, R. J., Capaldi, C. A., Carfagno, N. S., Chasten, K. T., Cleeremans, A., Connell, L., DeCicco, J. M., … Zwaan, R. A. (2016). Registered Replication Report: Strack, Martin, & Stepper (1988). Perspectives on Psychological Science , 11 (6), 917–928. https://doi.org/10.1177/1745691616674458 Footnotes Preliminary results of Experiment 1 involving 26 out of 60 participants have been accepted for publication as research notes in the Giornale Italiano di Psicologia (Ras et al, in press). Additional Declarations No competing interests reported. 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1\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-8252710/v1/bc36568b6d16bcb91b91f431.png"},{"id":97672567,"identity":"87be8f82-e588-41f9-96e0-297fdaf030fc","added_by":"auto","created_at":"2025-12-08 09:38:23","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":90845,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eMean Response Times (in Milliseconds) and SDs for Participants’ Ratings as a Function of the Expressed Emotion and Experimental Groups (Teeth vs Lips) in Experiment 1\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8252710/v1/45209962d25871eac6c9d022.jpeg"},{"id":97671637,"identity":"05de395a-92d4-4cf1-ae5c-4b7e1244bbe2","added_by":"auto","created_at":"2025-12-08 09:32:51","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":453871,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eExample of a Screen Shown to the Participants in Experiment 2 During Recognition\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8252710/v1/3c050060f7941692bf222578.jpeg"},{"id":97533900,"identity":"da5200f2-88b3-427e-8e8e-bad37b4b2342","added_by":"auto","created_at":"2025-12-05 13:46:49","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":102450,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eAccuracy Rates (Ms and SDs) for Face Recognition as a Function of the Type of Stimuli and the Group (Teeth vs Lips) in Experiment 2\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-8252710/v1/bc0ff29130b347806ba8ba6b.png"},{"id":97671868,"identity":"db466435-0800-4d72-87be-efe914b91165","added_by":"auto","created_at":"2025-12-08 09:33:12","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":132860,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eMean Response Times in Milliseconds and SDs of Face Recognition for Target Stimuli as a Function of the Emotion they Expressed and of the Group (Teeth vs Lips) in Experiment 2\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-8252710/v1/a34fc9969ec7266b73add557.png"},{"id":97533897,"identity":"8bded304-89b3-4875-8117-db19234cf9fa","added_by":"auto","created_at":"2025-12-05 13:46:49","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":58200,"visible":true,"origin":"","legend":"\u003cp\u003eUnnumbered image in the Experiment 1 section.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8252710/v1/1a6140756025588bb76127c6.png"},{"id":97678539,"identity":"ab4bf139-72b2-44bf-8850-7aa2f21c9544","added_by":"auto","created_at":"2025-12-08 09:55:38","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1654678,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8252710/v1/be05cbba-69f5-4f99-a855-cd855273cd68.pdf"},{"id":97533879,"identity":"bf0d8c06-ab2d-45b0-9876-ad1c1e1ed4d7","added_by":"auto","created_at":"2025-12-05 13:46:48","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":23642,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementarymaterials2511DEF.docx","url":"https://assets-eu.researchsquare.com/files/rs-8252710/v1/6622edd9134095c2dc8dc36e.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Facial Feedback on the Perception and Memory for Emotional Faces","fulltext":[{"header":"Public Significance Statement","content":"\u003cp\u003eThe purpose of our study is to increase the understanding of how facilitating/inhibiting smile influences both the perception and the memory of emotional faces. By unobtrusively manipulating the activation/inhibition of the zygomatic muscle (through the \u0026ldquo;pen-in-mouth procedure\u0026rdquo;) and by presenting happy, angry, and neutral expressions, our work aims to clarify whether this manipulation can affect how people evaluate (Experiment 1) and remember (Experiment 2) emotional information from human faces.\u003c/p\u003e"},{"header":"Introduction","content":"\u003cp\u003eThe Facial Feedback Hypothesis (FFH) posits that facial expressions can influence or even trigger emotional experiences, suggesting a crucial bidirectional relationship between facial muscle activity and emotions (Strack et al., 1988). Moreover, empirical findings suggest a relationship between bodily states and memory, i.e., a congruent posture between encoding and retrieval facilitates recall (e.g., Dijkstra et al., 2007). The aim of the present investigation is to employ the “pen-in-mouth procedure” used by Strack et al. (1988) to test the effects of facial manipulation both on perception and long-term memory for emotional faces. Regarding perception, Strack et al. (1988) found evidence in favor of the FFH: participants rated humorous cartoons more positively when their facial muscle activity was manipulated to facilitate smiling. The aim of Experiment 1 is to replicate the evidence supporting the FFH, by using the same procedure as in Strack et al. (1988) but different stimuli: happy faces instead of funny cartoons. Moreover, Experiment 1 examines the presence or absence of the facial feedback effect when participants evaluate angry faces.\u0026nbsp;With the intent to integrate the FFH with evidence of the congruency effect of bodily states on memory, Experiment 2 explores the potential beneficial effect on long-term memory when the observer’s facial expression and the observed one are congruent.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFacial Feedback Hypothesis and Perception\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe FFH has been widely debated in research concerning the nature of emotions. Although there are several variants of this theory, it is generally based on the idea that muscle feedback from facial expressions plays a causal or at least modulating role in emotional experience. This idea has several historical roots. Charles Darwin stated that “The free expression by outward signs of an emotion intensifies it. [...]. Even the simulation of an emotion tends to arouse it in our minds.” (1872, p. 366). Based on this premise, several researchers emphasized the importance not only of facial expression but more in general of bodily states in determining subjective emotional experiences.\u003c/p\u003e\n\u003cp\u003eOne of the most important theories advocating this approach was put forward by James (1884) who argued that emotions are essentially the perception of bodily changes rather than purely mental states:\u0026nbsp;“[…]\u0026nbsp;the more rational statement is that we feel sorry because we cry, angry because we strike, afraid because we tremble, and not that we cry, strike, or tremble, because we are sorry, angry, or fearful\u0026nbsp;[…]” (1884, p. 190). According to James, the process of emotional experience starts with an internal or external stimulus that triggers changes in the body’s state at a behavioral, physiological and expressive level. The perception of these changes gives rise to a subjective emotional experience. Emotions are therefore rooted in the body's reactions to stimuli and each emotion is characterized by specific changes in bodily states.\u003c/p\u003e\n\u003cp\u003eFollowing Darwin and James, Allport (1922) and later Tomkins (1962a, 1962b) emphasized the role of the facial muscles in producing and modulating emotional experience. In particular, Tomkins’ theory highlights the critical role of facial feedback in the subjective experience of emotions, suggesting that an internal or external emotional stimulus triggers an inborn “affect program” (1962a, p. 244) that transmits messages via motor and circulatory pathways to the face; the face then sends sensory feedback to the brain and when this feedback reaches consciousness, it is experienced as a specific emotion.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eCrucial for this topic, Ekman et al. (1983) showed that performing a directed facial action task, in which participants are instructed to contract specific facial muscles (e.g., for fear: “raise your brows and pull them together”, “now raise your upper eyelids”, “now also stretch your lips horizontally, back toward your ears”, p. 1208), produces different autonomic nervous system reactions for specific emotions and elicits the relative subjective feelings.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAlthough Ekman and colleagues were careful not to mention emotion labels, this methodology has been criticized by Strack et al. (1988) because participants were asked to mimic expressions corresponding to emotions. This could have led to the possibility that their awareness of mimicking emotion expressions induced the emotions rather than the facial feedback conceived as a purely implicit mechanism. Furthermore, participants’ awareness of imitating emotions may have led them to comply with the experimenters’ expectations.\u003c/p\u003e\n\u003cp\u003eTo address these potential shortcomings, Strack et al. (1988) tested the FFH with a novel experimental paradigm. Participants were told that the purpose of the study was to investigate the difficulty of performing tasks, such as writing or drawing, while holding a pen in their mouth, as people with a physical disability who cannot use their hands might do. One group held the end of a pen vertically with their teeth (facilitating smile), while the other group held the end of a pen vertically with their lips (inhibiting smile). This methodological approach was used to ensure that any emotional changes observed were due to the induced facial expressions and not to the participants’ awareness of the true aims of the study. While holding the pen, participants rated the funniness of cartoons. The authors hypothesized that holding the pen between the teeth would facilitate a smile and enhance the feeling of happiness, which in turn would lead to a more positive evaluation of the cartoons. The results confirmed the hypothesis, showing that participants in the teeth condition rated the cartoons as funnier than those in the lips condition. This study is considered revolutionary due to the introduction of the “pen-in-mouth procedure”: by facilitating or inhibiting a smile without explicit instructions, the authors addressed the criticism of demand characteristics and provided stronger evidence for the FFH. Nevertheless, various attempts to replicate these findings have produced controversial results (Coles et al., 2019).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTo clarify this issue, Wagenmakers et al. (2016) conducted a registered replication study involving 17 independent research groups that attempted to replicate the original study of Strack et al. (1988). Overall, the results showed no significant difference in funniness ratings between the teeth and lips conditions: out of 34 Bayesian analyses (two analyses for each replication attempt), only one provided evidence in favor of the alternative hypothesis. Noah et al. (2018; see also Strack, 2016) hypothesized that the failure to replicate the original study may be related to a critical procedural difference: in the replication study, but not in the original one, participants were aware that they were being videotaped. The authors tested this hypothesis by creating two experimental conditions, one characterized by the presence of a camera and the other by its absence. The results supported their hypothesis: the facial feedback effect was significant without a camera, but not when a camera was present. This suggests that awareness of being observed can negatively influence the facial feedback effect.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe findings of Noah et al. (2018) are further supported by Marsh et al. (2019), who conducted a\u0026nbsp;study involving undergraduate students exposed to the “pen-in-mouth procedure” while evaluating the funniness of cartoons without being video recorded. The authors found a significant difference in humor ratings between the two experimental conditions: cartoons rated while participants held the pen with the teeth were consistently evaluated as funnier than those rated while holding the pen with the lips. The results replicated the effect reported by Strack et al. (1988) and provided further evidence in favor of the FFH. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eOther studies investigated the FFH with the pen-in-mouth procedure, but also with other facial manipulations. We will discuss their results in relation to the ones of the present study in the General Discussion.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFacial Feedback Hypothesis and Long-Term Memory\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe encoding specificity principle states that it is easier to retrieve a memory when contextual elements present at encoding match those present during retrieval (Tulving \u0026amp; Thomson, 1973). Moreover, research has shown that memory retrieval involves sensorimotor pathways that simulate events occurred during encoding (for a review see Ianì, 2019). Thus, understanding how bodily states influence memory is crucial. Dijkstra et al. (2007) investigated the effect of posture congruency at encoding and recall. The authors hypothesized that assuming a posture congruent between encoding and retrieval facilitates recall. To test this hypothesis, participants were asked to recall autobiographical memories of specific events (e.g., the last dental visit) while taking postures that could be either congruent (i.e., lying on a recliner with their mouth open) or incongruent (i.e., standing upright with their hands on their hips). The results showed that participants recalled past experiences faster when assuming a congruent posture compared to an incongruent posture, both in the immediate and in the delayed recall test (two weeks later).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAnother study by Limata et al. (2021) addressed this topic by asking participants to perform actions on objects while standing or sitting at encoding. During the recall of the previously performed simple hands’ actions, half of the participants were standing, the other half were sitting. Contrary to the hypothesis, congruent postures during encoding and retrieval did not improve accuracy, suggesting that posture, understood as a simple static position of the body, has no influence on the retrieval process of the actions performed by participants. Conversely, Limata et al. (2023) have shown that body posture can influence memory in a recognition task when the posture is manipulated in a way that is crucial for the execution (and the potential execution) of actions. During encoding, participants observed a series of objects and performed actions on another series of objects using upper limbs. During recognition, participants of one group held their hands in front of them (non-interfering posture), and participants of a second group behind their back (interfering posture). Participants with a non-interfering posture recognized enacted objects faster than observed ones, but this advantage vanished for the interfering posture group. This indicates that an inconsistent posture with the encoding action affects memory in terms of reaction times.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eDespite the evidence for the relationship between bodily states and memory (Ianì, 2019), there is a notable lack of research on how facial muscle manipulation through the “pen-in-mouth procedure” can affect memory. To our knowledge, there is only one study addressing this topic: Kuehne et al. (2021) attempted to investigate in what ways the manipulation of facial feedback by induced smiling influences the immediate recall of emotional facial expressions. In this study participants were asked to carry out a working memory task on happy and sad faces while holding a pen between their teeth (facilitating smile) or with their non-dominant hand. More specifically, the participants were presented with happy or sad faces of varying intensities during encoding. After each target face, a neutral face was presented and participants had to reproduce the target facial expression by scrolling the mouse wheel: by scrolling up, participants could assign different intensities of happiness to the neutral face; by scrolling down, they could assign different intensities of sadness. The results showed that the participants in the teeth condition reproduced happy faces with higher accuracy. This shows how the facilitation of smiling selectively improves the immediate memory of happy faces.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eOverview of the Present Study\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe conducted two experiments by using the “pen-in-mouth procedure” as in Strack et al. (1988) to test the FFH on the perception of emotional faces (Experiment 1) and the memory of emotional faces (Experiment 2). We used the “pen-in-mouth procedure” to shed light on the controversial results obtained through this manipulation. Moreover, this procedure appears to be the best way to limit participants’ awareness of the true aim of the experimental conditions (smile facilitation vs inhibition, Coles et al. 2022). In Experiment 1 we used the “pen-in-mouth procedure” to test whether the participants’ own facial expression influences their evaluation in terms of valence of angry, neutral, and happy faces. Crucially, our experimental manipulation includes angry faces, whereas Strack et al. (1988) only used positively connoted stimuli (humorous cartoons). Experiment 2 investigates the relationship between the facial muscles’ activity manipulated by the “pen-in-mouth procedure” and long-term memory for angry, neutral, and happy faces. The same kind of stimuli (angry, neutral, and happy faces from the KDEF, Karolinska Directed Emotional Faces, Lundqvist et al., 1998) were used in the two experiments. Both experiments were approved by the Bioethical Committee of the University of Turin. For each experiment we report how we determined our sample size, all data exclusions, all manipulations and all measures. Table S1 in the Supplementary Materials reports the allocation of men and women to the groups (teeth vs lips) for the two experiments.\u003c/p\u003e"},{"header":"Experiment 1: Do Observers’ Facial Expressions Modulate the Perception of Observed Angry, Neutral and Happy Faces?","content":"\u003cp\u003eExperiment 1 focuses on the role that the observer\u0026rsquo;s facial expression plays in modulating the valence evaluation of angry, neutral, and happy faces. Based on Strack et al. (1988), we hypothesised that when the observer\u0026rsquo;s muscle activity associated with smiling is facilitated, happy faces should be rated more positively than when it is inhibited. If this prediction holds, the results will provide support for the FFH regarding emotional expression perception. With respect to angry and neutral faces, we do not have specific predictions: to our knowledge, most of the studies on perception employing the \u0026ldquo;pen-in-mouth procedure\u0026rdquo; focused exclusively on positively connoted stimuli. Soussignan (2002) conducted the only study that employed this procedure with participants rating their reaction to both positive and negative emotionally connoted stimuli (i.e., videoclips). The author replicated Strack et al.\u0026rsquo;s (1988) results with higher positive reactions for positively connoted stimuli when smiling was facilitated. No significant difference was detected in the reactions to negative stimuli, regardless of the position of the pen.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe participants\u0026rsquo; task was to rate the emotional valence of angry, neutral, and happy faces on a 7-point Likert scale, ranging from extremely negative to extremely positive. Half of the participants held the pen between their lips, a pose that inhibits smiling, and the other half held the pen between their teeth, a pose that facilitates smiling.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethod\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eParticipants\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo determine the required sample size, an a priori power analysis based on an effect size of \u003cem\u003ed\u003c/em\u003e = 0.66 derived from a similar study (Soussignan, 2002) was conducted using G*Power (Version 3.1.9.7; Faul et al., 2007). Since we had a specific hypothesis only for happy faces, we ran a power analysis for a one-tailed independent-samples t test assessing the difference in ratings for happy faces between two groups (teeth vs lips). The significance level was set at \u0026alpha; = .05, with desired power (1 \u0026ndash; \u0026beta;) = .80. The results indicated that a total sample size of 60 participants (30 per group) would be sufficient to detect the expected effect.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe 61 participants (26 men, 35 women, mean age = 24.21 years, \u003cem\u003eSD\u003c/em\u003e = 4.52) were students at the University of Turin. Data from one participant was excluded from the analyses because instead of holding firmly the pen between her lips she let it slide down and played with it. Therefore, the final sample was composed of 60 participants (26 men, 34 women, mean age = 24.28 years, \u003cem\u003eSD\u003c/em\u003e = 4.52). All participants were Italian, a minority of them (\u003cem\u003en\u0026nbsp;\u003c/em\u003e= 3) had foreign origins but were grown in Italy and were fluently speaking Italian. Because the FFH is discussed in many psychology classes, we recruited participants from other university courses. They voluntarily participated in the experiment in exchange for academic credit.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eMaterials\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe material consisted of 18 faces of 18 different actors selected from the KDEF database (Lundqvist et al., 1998), with 6 faces belonging to each of the following categories: angry, neutral, happy. The faces in each category belong to 3 women and 3 men. We used a 7-point Likert scale ranging from 0 (\u003cem\u003eextremely negative\u003c/em\u003e) to 6 (\u003cem\u003eextremely positive\u003c/em\u003e), with intermediate values of 1 (\u003cem\u003enegative\u003c/em\u003e, 2 (\u003cem\u003eslightly negative\u003c/em\u003e), 3 (\u003cem\u003eneutral\u003c/em\u003e), 4 (\u003cem\u003eslightly positive\u003c/em\u003e), 5 (\u003cem\u003epositive\u003c/em\u003e), to assess the emotional valence participants assigned to each stimulus. To calculate response times, the Likert scale was structured in a semicircular shape with the mouse automatically positioned equidistantly from each label.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eProcedure\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe experiment was conducted in a single, individual session in a quiet room. Participants were randomly assigned to two experimental groups: in the TEETH group they were invited to vertically hold a pen between the teeth (facilitating smile), and in the LIPS group they were invited to vertically hold a pen between the lips (inhibiting smile) (see Figure 1 in Strack et al. 1988, p. 771). During the experimental session, participants were video recorded with a hidden mini camera to control whether they held the pen correctly. We made sure that they were not aware of being video recorded to avoid the inhibiting effect on the facial feedback observed in Noah et al. (2018). At arrival the experimenter asked the participant to sign the informed consent and then to sit in front of a computer to read with the experimenter the following instructions on the computer screen:\u003c/p\u003e\n\u003cp\u003eThank you for taking part in this study. You will see a series of photos showing faces. For each photo, you have the task of judging the extent to which the emotion expressed by the person is negative or positive.Shortly after each photo, a scale appears on which you can give your rating from \u0026ldquo;extremely negative\u0026rdquo; to \u0026ldquo;extremely positive\u0026rdquo;. You must use the mouse to enter your rating. We ask you not to let go of the mouse until the end of the experimental session. The scale is the following:\u003c/p\u003e\n\u003cp\u003eTry to answer spontaneously without thinking too much about it.\u003c/p\u003e\n\u003cp\u003ePress the space bar for further instructions.\u003c/p\u003e\n\u003cp\u003eWe also ask you [to hold this pen between your teeth without touching it with your lips/to hold this pen between your lips without touching it with your teeth] for the whole duration of the experimental session. Before you start, we ask you to place the mouse in a position that is comfortable for you. Once the experimental session is finished, we ask you to knock on the door of the room.\u003c/p\u003e\n\u003cp\u003ePress the space bar when you want to start.\u003c/p\u003e\n\u003cp\u003eAfter reading the instructions, right before the beginning of the task, the experimenter made sure that the participant was holding the pen correctly between the teeth or lips and left the room.\u003c/p\u003e\n\u003cp\u003eEach participant was shown a total of 18 faces. Each face was presented for 5 seconds and immediately afterwards the 7-point Likert scale appeared on the screen on which the participants were asked to rate the emotional valence of the face they had just seen. After the rating, a new face appeared on the computer screen. The stimuli were presented on the computer screen with E-Prime 3.0 (Psychology Software Tools, 2020). They appeared in random order with the only constraint that two faces of the same valence were not presented consecutively. We recorded the emotional valence ratings of each face and the relative reaction times.\u003c/p\u003e\n\u003cp\u003eAt the end of the experimental session, participants were asked to read and sign the post-study consent form. They were informed they had been videotaped (none of them noticed the hidden camera) and asked again whether they consent or not to the use of their data and the video recording. After the experimenter had obtained consent for this use, participants were informed of the aims of the study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults\u003cstrong\u003e\u003csup\u003e1\u003c/sup\u003e\u003c/strong\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFigure 1 shows the participants\u0026rsquo; mean ratings for the facial expressions on the emotional valence scale in the two experimental conditions: pen between the teeth and pen between the lips. Exact means and standard deviations are provided in Table S2 in the Supplementary materials.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFigure 1\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eMeans and Standard Deviations for Participants\u0026rsquo; Valence Ratings as a Function of the Type of Stimuli and Experimental Groups (Teeth vs Lips) in Experiment 1\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eSince ordinal data can be treated as continuous (Robitzsch, 2020), we considered valence ratings as a continuous variable to ensure methodological consistency with the analyses of Experiment 2. A 2 (GROUP: Teeth, Lips) x 3 (EMOTION: Angry, Happy, Neutral) mixed ANOVA was conducted on the rating scores. Mauchly\u0026rsquo;s test indicated that the assumption of sphericity was violated for the Emotion within-subjects variable, \u0026chi;\u0026sup2;(2) = 11.56, \u003cem\u003ep\u003c/em\u003e = .003; therefore, Huynh\u0026ndash;Feldt\u0026ndash;corrected degrees of freedom are reported.\u003c/p\u003e\n\u003cp\u003eThere was a significant main effect of EMOTION (\u003cem\u003eF\u003c/em\u003e(1.77, 102.37) = 967.58, \u003cem\u003ep\u003c/em\u003e \u0026lt; .001, \u0026eta;p\u0026sup2; = .943), while the main effect of GROUP was not significant (\u003cem\u003eF\u003c/em\u003e(1, 58) = 0.09, \u003cem\u003ep\u003c/em\u003e = .768, \u0026eta;p\u0026sup2; = .002). This shows how, regardless of the pen manipulation, neutral faces were rated more positively than angry ones and happy faces were rated more positively than neutral ones.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eCrucially, the EMOTION\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eby\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eGROUP\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003einteraction was statistically significant (\u003cem\u003eF\u003c/em\u003e(1.77, 102.37) = 3.28, \u003cem\u003ep\u003c/em\u003e = .048, \u0026eta;p\u0026sup2; = .054). To follow up this interaction, independent samples t-tests were conducted for each emotional condition. For happy stimuli, ratings were significantly higher in the teeth group compared to the lips group (\u003cem\u003et\u003c/em\u003e(58) = 2.75, \u003cem\u003ep\u003c/em\u003e = .008, \u003cem\u003ed\u003c/em\u003e = 0.71, mean difference = 0.26, 95% CI [0.07, 0.44]). For angry stimuli the comparison between teeth and lips was not significant (\u003cem\u003et\u003c/em\u003e(58) = 1.25, \u003cem\u003ep\u003c/em\u003e = .218). Levene\u0026rsquo;s test suggested unequal variances (\u003cem\u003eF\u003c/em\u003e(1, 58) = 4.67, \u003cem\u003ep\u003c/em\u003e = .035); however, the adjusted test with corrected degrees of freedom led to the same conclusion (\u003cem\u003et\u003c/em\u003e(45.41) = \u0026ndash;1.25, two tailed \u003cem\u003ep\u003c/em\u003e = .219 \u003cem\u003ed\u003c/em\u003e = 0.32, mean difference = \u0026ndash;0.22, 95% CI [-0.57, 0.13]). For neutral stimuli no significant difference was found between groups (\u003cem\u003et\u003c/em\u003e(58) = \u0026minus;0.97, two tailed \u003cem\u003ep\u003c/em\u003e = .336, \u003cem\u003ed\u003c/em\u003e = 0.25, mean difference = -0.09, 95% CI [-0.29, 0.10]).\u003c/p\u003e\n\u003cp\u003eTaken together, these results indicate that, although the groups did not differ in overall rating levels, they differed specifically in their evaluations of happy faces, with the teeth group giving significantly more positive ratings than the lips group.\u003c/p\u003e\n\u003cp\u003eFigure 2 shows the response times of the participants when evaluating the emotional valence of the faces in the two experimental conditions: pen between the teeth and pen between the lips. Exact means and standard deviations are provided in Table S3 in the Supplementary materials.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFigure 2\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eMean Response Times (in Milliseconds) and SDs for Participants\u0026rsquo; Ratings as a Function of the Expressed Emotion and Experimental Groups (Teeth vs Lips) in Experiment 1\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eA 2 (GROUP: Teeth, Lips) x 3 (EMOTION: Angry, Happy, Neutral) mixed repeated-measures ANOVA was conducted on Reaction Times. Because Mauchly\u0026rsquo;s test indicated a violation of sphericity, the Huynh\u0026ndash;Feldt correction was applied to the within-subjects factor.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThere was a significant main effect of EMOTION (\u003cem\u003eF\u003c/em\u003e(1.91, 110.90) = 22.60, \u003cem\u003ep\u003c/em\u003e \u0026lt; .001, \u0026eta;p\u0026sup2; = .280), indicating that participants\u0026rsquo; response times differed across the three emotional conditions. Bonferroni-adjusted pairwise comparisons showed that angry faces elicited significantly slower responses than both the happy (\u003cem\u003ep\u003c/em\u003e \u0026lt; .001, mean difference = 635.33, 95% CI [367.97, 902.70]) and neutral ones (\u003cem\u003ep\u003c/em\u003e \u0026lt; .001, mean difference = 664.81, 95% CI [351.49, 978.13]). No significant difference emerged between the happy and neutral faces (\u003cem\u003ep\u003c/em\u003e = 1.000, mean difference = 29.48). No main effect of GROUP was found (\u003cem\u003eF\u003c/em\u003e(1, 58) = 0.063, \u003cem\u003ep\u003c/em\u003e = .803, \u0026eta;p\u0026sup2; = .001). There was no interaction effect between EMOTION and GROUP (\u003cem\u003eF\u003c/em\u003e(1.91, 110.90) = 0.094, \u003cem\u003ep\u003c/em\u003e = .91, \u0026eta;p\u0026sup2; = .002).\u003c/p\u003e\n\u003cp\u003eOverall, the results show that, in line with the FFH, happy faces were rated more positively when the activation of the zygomatic muscle was facilitated. This finding is consistent with Strack et al. (1988), where positive stimuli (funny cartoons) were rated more positively in the teeth condition than in the lips condition. Our results also show longer reaction times when evaluating angry faces compared to happy and neutral faces. This may be because negative stimuli require longer cognitive processing than positive or neutral stimuli due to the threatening values they may carry (Baumeister et al., 2001).\u003c/p\u003e"},{"header":"Experiment 2: Do Observers’ Facial Expressions Modulate Long-Memory of Observed Angry, Neutral and Happy Faces?","content":"\u003cp\u003eThe aim of Experiment 2 was to investigate whether the observer\u0026rsquo;s facial expressions modulate the memory of previously seen emotional faces. Using the same facial manipulation as in Experiment 1, we tested whether congruency between the observer\u0026rsquo;s facial expression and the emotion conveyed by the observed face favors recognition.\u003c/p\u003e\n\u003cp\u003eThe experiment consisted of two phases. In the encoding phase, participants observed 24 stimuli, equally divided into 8 angry, 8 neutral, and 8 happy faces. To ensure they processed the emotional expression, participants were asked to rate the positive or negative emotional state of the person depicted in each photo. In the recognition phase, participants encountered 24 screens, each depicting the same actor with an angry, happy, and neutral face. For each actor, only one of the three facial expressions had been shown during encoding. The participant\u0026rsquo;s task was to identify this expression while going through the \u0026ldquo;pen-in-mouth procedure\u0026rdquo;.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethod\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eParticipants\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA power analysis revealed that at least 24 participants were required to reach an appropriate statistical power of 0.95 to detect a significant effect (with \u0026alpha; = 0.05), assuming a medium effect size (\u003cem\u003ef\u003c/em\u003e = 0.35,\u0026nbsp;\u0026eta;\u003csub\u003ep\u003c/sub\u003e\u003csup\u003e2\u003c/sup\u003e=0.109), the same found by Kuehne et al. (2021), who conducted a similar study on the effect of facial expression manipulations on immediate recall. The sample size was determined using the G-Power software (Version 3.1.9.6; Faul et al., 2007).\u0026nbsp;To recruit participants, we offered students from the University of Turin the opportunity to earn credits. The participants had not taken part in Experiment 1. All participants were Italian. For the same reasons discussed in Experiment 1, we recruited students not attending a psychology course.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eWe tested a total of 28 participants but data from 2 participants was removed from the analyses: one participant was aware of the FFH and the \u0026ldquo;pen-in-mouth procedure\u0026rdquo;, while a second participant encountered a technical problem (blocking of the response keys) during the experiment. Thus, the final sample consisted of 26 participants (14 men, 12 women, mean age = 24.41 years, \u003cem\u003eSD\u003c/em\u003e = 4.31).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eMaterials\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe material consisted of the 72 pictures of 24 different actors from the KDEF database (Lundqvist et al., 1998). Each actor was represented in three photos with 3 different facial expressions (angry, happy, neutral).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eProcedure\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe experiment was conducted in a single, individual session in a quiet room. As in Experiment 1, participants were randomly assigned to the LIPS or the TEETH condition.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFor both groups, the experiment consisted of two phases, encoding and recognition, interrupted by a distractor task At their arrival participants were asked to read and sign the informed consent form. Then they were asked to sit in front of a computer to begin the encoding phase. The following instructions were read by the participant together with the experimenter:\u003c/p\u003e\n\u003cp\u003eThank you for your participation. You will be presented with photos of faces and your task is to rate how negative or positive the emotion expressed by the person is. Immediately after each photo is presented, a scale appears that allows you to rate it from extremely negative to extremely positive. Please use the mouse to express your evaluation.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTry to answer spontaneously without thinking too much about it.\u003c/p\u003e\n\u003cp\u003ePress the space bar when you want to start.\u003c/p\u003e\n\u003cp\u003eDuring the encoding phase, each participant was presented with 24 faces for 5 seconds each. Immediately after the presentation of each face, the same 7-point Likert scale used in Experiment 1 appeared on the screen, on which the participants rated the emotional valence of the face they had just observed. The ratings obtained were not considered a dependent variable and had only the goal of ensuring that the participants\u0026rsquo; attentive resources were directed towards the stimuli.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eAfter completing the encoding phase, each participant performed a ten-minute distractor task consisting in finding differences between pairs of vignettes. No faces or emotions were shown in these cartoons to avoid interference with the experimental material. Then the experimenter entered the room and instructed the participant for the recognition phase. The instructions for the recognition task were the following:\u003c/p\u003e\n\u003cp\u003eIn this phase you will see a series of screens, each composed of three photos of the same actor. In each screen, one of the three photos has already been presented to you in the previous phase: your task is to identify it.\u003c/p\u003e\n\u003cp\u003eTo answer, press the left arrow to indicate the photo shown on the left, the down arrow to indicate the central image, the right arrow to indicate the photo shown on the right of the screen.\u003c/p\u003e\n\u003cp\u003eWe ask you to give the answer as soon as you are sure by pressing the corresponding key.\u003c/p\u003e\n\u003cp\u003eFor the duration of the experiment, keep the fingers of one hand resting on the labeled keys.\u003c/p\u003e\n\u003cp\u003eWe also ask you [to hold this pen between your teeth/lips without touching it with your lips/teeth].\u003c/p\u003e\n\u003cp\u003ePress the space bar when you want to start.\u003c/p\u003e\n\u003cp\u003eAfter reading the instructions and before leaving the room, the experimenter made sure that the participant was holding the pen correctly between the teeth or lips. During this phase, participants in both groups were presented with 24 screens, each displaying three photographs of the same actor: one with an angry expression, one with a neutral expression, and one with a happy expression (see Fig. 3).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFor each displayed screen, only one of the three photographs was shown during encoding. The participant\u0026rsquo;s task was to identify the previously seen photo by pressing one of the three QWERTY-keyboard keys V, B, N, respectively labeled with a left, down, or right arrow. To permit an accurate measurement of reaction times, participants were instructed to keep three fingers of the same hand resting on the response keys throughout the whole recognition phase. The stimuli were presented on the computer screen with E-Prime 3.0 (Psychology Software Tools, 2020). We recorded the recognition accuracy and the reaction times for each displayed screen. The order of presentation of the different actors was randomized as well as the position of the different emotional expressions. In this phase, the participants were video recorded with a hidden mini camera. The purpose of the video recording was to ensure that the pen was well positioned and that the participant kept three fingers of the same hand resting on the answer keys for the entire duration of the task.\u003c/p\u003e\n\u003cp\u003eAfter completing the recognition task, the experimenter asked the participant to read and sign the post-test consent form where they were informed that they had been videotaped. After obtaining consent for this use, the experimenter shared with each participant the aims of the study and asked if they had noticed that they had been video recorded (none of them noticed the hidden camera) and if they had any previous knowledge about the FFH or the pen-in-mouth procedure.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFigure 4 shows the participants\u0026rsquo; mean accuracy rates in discriminating seen and unseen faces as a function of the displayed EMOTION (Angry, Neutral, Happy) and of the GROUP (Teeth vs Lips). Exact means and standard deviations are provided in Table S4 in the Supplementary materials.\u003c/p\u003e\n\u003cp\u003eA\u0026nbsp;2 (GROUP: Teeth, Lips) x 3 (EMOTION: Angry, Happy, Neutral) mixed ANOVA was conducted to examine the effects of facial manipulation and emotional facial expressions on accuracy. The main effect of EMOTION was significant (\u003cem\u003eF\u003c/em\u003e(2, 48) = 6.72, \u003cem\u003ep\u003c/em\u003e = .003, \u0026eta;ₚ\u0026sup2; = .219). A post-hoc comparison with Bonferroni correction revealed that angry faces were recognized more accurately than happy (\u003cem\u003ep\u003c/em\u003e = .014, mean difference = 0.10, CI [0.02, 0.18]) and neutral (\u003cem\u003ep\u003c/em\u003e = .005, mean difference = 0.11, CI [0.03, 0.19]) faces. No difference was found between happy and neutral faces (\u003cem\u003ep\u003c/em\u003e = 1.00, mean difference = 0.01, CI [-0.09, 0.10]). The main effect of GROUP was not significant (\u003cem\u003eF\u003c/em\u003e(1, 24) = 1.49, \u003cem\u003ep\u003c/em\u003e = .234, \u0026eta;ₚ\u0026sup2; = .058). The interaction between EMOTION and GROUP was not significant (\u003cem\u003eF\u003c/em\u003e(2, 48) = 0.12, \u003cem\u003ep\u003c/em\u003e = .884, \u0026eta;ₚ\u0026sup2; = .005).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFigure 5 shows the mean response times in discriminating seen and unseen faces as a function of the emotion they expressed and of the participants\u0026rsquo; posture. Exact means and standard deviations are provided in Table S5 in the Supplementary materials.\u003c/p\u003e\n\u003cp\u003eA 2 (GROUP: Teeth, Lips) x 3 (EMOTION: Angry, Happy, Neutral) mixed ANOVA was conducted to examine the effects of facial manipulation and emotional facial expressions on reaction times. There was no significant main effect of EMOTION (\u003cem\u003eF\u003c/em\u003e(2, 24) = 1.62, \u003cem\u003ep\u003c/em\u003e = .209, \u0026eta;ₚ\u0026sup2; = .063). There was no significant main effect of GROUP (\u003cem\u003eF\u003c/em\u003e(1, 24) = 2.29, \u003cem\u003ep\u003c/em\u003e = .143, \u0026eta;ₚ\u0026sup2; = .087). The interaction between EMOTION and GROUP was also not significant (\u003cem\u003eF\u003c/em\u003e(2, 24) = 1.26, \u003cem\u003ep\u003c/em\u003e = .293, \u0026eta;ₚ\u0026sup2; = .050).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eOverall, there was no effect of facial feedback on long-term memory for emotional faces. Furthermore, the results show that angry faces were better recognized in the long-term memory task than neutral and happy faces. This advantage for angry facial expressions may be explained by their greater evolutionary relevance: threatening stimuli tend to capture attention more strongly (as shown by the longer reaction times for angry faces in Experiment 1) and to be encoded more deeply in memory. This is consistent with Kensinger (2007), who showed that the valence of a memory influences recall accuracy, with negative memories remembered in greater detail than positive ones. Similarly, our results suggest that negative emotional stimuli, such as angry faces, may enhance long-term memory retention due to their intrinsic evolutionary significance as a sign of potential threat.\u003c/p\u003e"},{"header":"General Discussion","content":"\u003cp\u003eThe present study examined the role of facial feedback in the perception and memory of emotions by employing the \u0026ldquo;pen-in-mouth procedure\u0026rdquo; across two experiments, using different emotional facial expressions (angry, neutral, and happy faces) as stimuli. Experiment 1 demonstrated that inducing participants to hold a smile-facilitating posture (pen between teeth) affected their emotional perception, leading them to rate happy faces more positively than those with a smile-inhibiting posture (pen between lips). There was no significant difference between the teeth and lips conditions for neutral and angry faces. The results concerning happy faces are consistent with Strack et al. (1988), who observed that funny cartoons were rated more positively in the smile-facilitating condition than in the smile-inhibiting condition.\u003c/p\u003e\n\u003cp\u003eExperiment 2 revealed no significant effect of participants\u0026rsquo; facial posture on recognition accuracy for previously seen emotional faces, suggesting that the influence of facial feedback may be limited to the perceptual domain rather than memory processes. This does not align with previous studies showing that posture can influence memory in recall or recognition tasks (Dijkstra et al., 2007; Limata et al., 2023). The results of Experiment 2 may be explained by two key differences from these studies. First, Experiment 2 examined the effects of congruency between the expression in the stimuli and the participants\u0026rsquo; expression, rather than the effects of body congruency between encoding and recognition. Secondly, it examined long-term memory for facial expressions, a type of stimulus not used in other studies on the relationship between bodily states and memory.\u003c/p\u003e\n\u003cp\u003eInterestingly, Experiment 2 revealed that, regardless of the facial manipulation, angry faces are recognized more accurately than neutral and happy faces, while Experiment 1 showed that angry faces require more attentional resources to be evaluated. This is consistent with studies suggesting that our cognitive resources are biased towards prioritizing the recognition of potentially harmful stimuli (Barros et al., 2023). Taken together, these results support the idea that threatening stimuli are intrinsically more relevant due to their importance for survival (Baumeister et al., 2001; Kensinger, 2007).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe results of the two experiments indicate that manipulating facial muscles using the \u0026ldquo;pen-in-mouth procedure\u0026rdquo; influences perception, but not long-term memory for emotional faces. As other studies have used different facial manipulations to investigate the FFH, it is not easy to compare their results with the present findings. For example,\u0026nbsp;Coles et al. (2019) conducted a meta-analysis and, by considering 286 effect sizes from 138 studies, found a significant, though small, overall effect of facial feedback on subjective emotional experience. However, the studies included in this meta-analysis also used facial manipulations that differ from the \u0026ldquo;pen-in-mouth procedure\u0026rdquo;, such as facial mimicry and the directed facial action task.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eGiven the contrast between the failed replication by Wagenmakers et al. (2016) and the results of Coles et al. (2019) providing evidence in favor of the FFH, Coles et al. (2022) conducted a further multi-lab test involving 26 laboratories and 3,878 participants from 19 countries. Participants rated either positive or neutral pictures while holding either a neutral or a happy facial expression. To elicit a happy expression, each participant completed the task in one of three conditions: (a) mimicry of images of actors displaying happiness, (b) voluntary facial action task, or (c) \u0026ldquo;pen-in-mouth procedure\u0026rdquo;. The authors found a clear facial feedback effect when facial mimicry and the voluntary facial action task were used, while the \u0026ldquo;pen-in-mouth procedure\u0026rdquo; produced less conclusive evidence. Nonetheless, when some participants\u0026rsquo; inclusion criteria were relaxed (e.g., performing the task on a device other than a laptop or personal computer), the analysis provided strong support for the facial feedback effect in the pen-in-mouth task as well. It should be highlighted that participants were significantly less aware of the study purposes in the pen-in-mouth condition compared to the two other facial manipulation conditions.\u003c/p\u003e\n\u003cp\u003eOther researchers used the same stimuli as in our study (emotional facial expressions), but the facial manipulations differed. For example, in a study by Blaesi and Wilson (2010), participants viewed 11 randomized photos of the same face on a continuum from smiling to frowning. For each photo, participants were asked to say whether the face was happy or sad. Each participant viewed the stimuli under two conditions. In the Pen condition, they were instructed to hold a pen horizontally (rather than vertically as in Strack et al., 1988) with their teeth, without touching it with their lips. This manipulation was intended to favor a smile. In the No Pen condition, participants received no special instructions. For each participant, the percentage of \u0026ldquo;happy\u0026rdquo; responses for each of the 11 stimuli was determined separately for the two conditions. The threshold for perceiving the face as happy was defined as 50% \u0026ldquo;happy\u0026rdquo; responses. For each participant, the thresholds for the conditions with and without the pen were compared, showing a lower threshold to perceive a happy expression in the Pen condition. According to the authors, this study shows how simulating a slight smile lowers the recognition threshold for happy faces. Similar results were found by Marmolejo-Ramos et al. (2020, Experiment 1, but see also Marmolejo-Ramos \u0026amp; Dunn, 2013, Experiments 5 and 6).\u003c/p\u003e\n\u003cp\u003eIn another study by Oberman et al. (2007, Experiment 2), participants completed four within-subject blocks, each consisting of a series of photos of happy, sad, fearful, or disgusted faces morphed to produce seven levels of intensity. They completed the four blocks under the following conditions: bite (holding a pen horizontally by exerting continuous pressure with the teeth), gum (chewing), lips (holding a pen horizontally with the lips), and rest (baseline). The authors intended the \u0026ldquo;lips\u0026rdquo; and \u0026ldquo;rest\u0026rdquo; manipulations as control conditions, while the \u0026ldquo;bite\u0026rdquo; and \u0026ldquo;gum\u0026rdquo; conditions were designed to create irrelevant muscular noise that blocks facial mimicry. On each trial, participants were shown a face and asked to rate the facial expression as conveying happiness, sadness, fear, or disgust. The results showed that the \u0026ldquo;bite\u0026rdquo; condition specifically impairs the ability to recognize happy faces and, to some extent, disgusted faces. According to the authors, this can be explained by the mimicry-blocking effect of the \u0026ldquo;bite\u0026rdquo; condition.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003ePonari et al. (2012, Experiment 1) explored the effects of interfering muscle contractions of the top- or bottom-half of participants\u0026rsquo; face on the ability to recognize fear, happiness, anger, disgust, sadness, and surprise expressions. They hypothesized that if facial manipulation is causally involved in emotion recognition, then an interfering contraction of face muscles involved in the production of a certain expression should impair the recognition of the very same expression. Participants were assigned to one of the following experimental conditions: (a) active contraction of the muscles in the lower part of their face (\u0026ldquo;lower\u0026rdquo; manipulation), i.e. placing a Chinese chopstick horizontally in the mouth while exerting constant pressure with the teeth without the lips touching the chopstick; (b) active contraction of the muscles in the upper part of the face (\u0026ldquo;upper\u0026rdquo; manipulation), i.e. to draw together two small round stickers placed near the inner edge of the eyebrows; (c) no muscle contraction (control condition). Participants\u0026rsquo; task was to identify the emotion conveyed by a face displayed on a computer screen. The results showed that the lower manipulation impaired the ability to recognize happiness and disgust, the upper manipulation impaired the recognition of anger, while both manipulations reduced the recognition of fear.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eInterestingly, the above studies that used emotional faces as stimuli employed a different version of the \u0026ldquo;pen-in-mouth procedure\u0026rdquo; from that of Strack et al. (1988): participants had to hold a pen/chopstick horizontally (not vertically) between their teeth. Furthermore, the authors\u0026rsquo; intention in using this facial manipulation were very different: while Blaesi and Wilson (2010) aimed to create a smile-facilitating condition, Oberman et al. (2007) and Ponari et al. (2012) respectively aimed to create irrelevant muscular noise that blocks facial mimicry or interferes with muscle contractions of the bottom-half of participants\u0026rsquo; face.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTo sum up, studies in literature not only used different methods to test the FFH, but also when they employed the \u0026ldquo;pen-in-mouth procedure\u0026rdquo; they used a different variant (e.g., holding the pen horizontally vs vertically). In some cases, even when the variant was the same, the intents differed (e.g., inducing smile vs muscular noise). The lack of consistency in both methodology and intents may have contributed to the controversial results on the FFH.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eLimitations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDue to the difficulties in conducting power analyses for mixed-effects models, in both experiments we used repeated-measures ANOVA and by doing so, we considered an ordinal variable (valence ratings in Experiment 1) as continuous. While our approach is widely used (Robitzsch, 2020), it represents a limitation because it does not fully account for the variability explained by random factors.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eMoreover, the generalizability of findings in emotional research is often constrained by cultural differences. Mesquita and Frijda (1992) highlight how emotional evaluations are shaped by culture, suggesting that results from one cultural group may not apply universally. Our study, conducted exclusively with W.E.I.R.D. (Western, Educated, Industrialized, Rich, and Democratic) students, reflects this limitation. Future research should account for cultural and socio-economical variability to ensure broader applicability of findings.\u003c/p\u003e"},{"header":"Conclusions and Future Research","content":"\u003cp\u003eOur findings contribute to a deeper understanding of the FFH by delineating its boundary conditions across different domains. Experiment 1 detected no significant difference between the teeth and lips conditions for neutral and angry faces. These findings suggest that manipulating smiles using the \u0026ldquo;pen-in-the-mouth procedure\u0026rdquo; affects the evaluation of happy faces, but not neutral or angry ones. Experiment 2 revealed no significant effect of facial muscle manipulation. Taken together, the results of our two experiments suggest that although facial feedback can influence immediate perceptual judgments of emotional expressions, it does not appear to play a role in long-term memory processes. These differences may reflect the fact that the perceptual and memory-related functions of emotional feedback engage different neural circuits and processes. For example, the perception of facial expressions may engage the mirror systems involved in immediate emotional understanding (Tramacere \u0026amp; Ferrari, 2016), whereas memory for facial expressions may rely more heavily on the hippocampal and prefrontal pathways (Sergerie et al., 2005), which may not be directly modulated by facial muscle activity. To summarize, our findings suggest that facial muscle activity plays an important role in modulating the perception of emotional expressions. However, the influence of facial feedback on long-term memory is not clear, suggesting that perceptual and memory processes may rely on facial muscle feedback in different ways. This research highlights the need for further investigation into the effects of facial feedback in different cognitive domains and emphasizes the complexity of theories of embodied emotion (Barsalou, 2008). Of interest for future research could be to further investigate the effect we found in Experiment 1 and to assess both the objective valence and the subjective feeling elicited by emotional faces.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePractical Implications\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe relevance of the proposed study is based on its potential impact on social interaction. Several studies show indeed that facial mimicry can enhance affiliation, pro-social behavior and empathy (e.g., Hess, 2021; Lakin \u0026amp; Chartrand, 2003). This could be particularly relevant in psychotherapeutic settings. In these contexts, the awareness that one\u0026rsquo;s own facial expression modulates the perception of the faces of others and the emotions expressed by them can be the subject of examination and reflection in the therapist/patient dyad. Regarding memory, our experiments didn\u0026rsquo;t reveal significant effects. Further research could explore the relationship between facial expressions and memory, offering insight into the field of eyewitness psychology.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003ch2\u003eConflict of Interest Statement\u003c/h2\u003e\u003cp\u003eThe authors report there are no competing interests to declare.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e\u003cp\u003eThis work was supported by the Italian Ministry of Education, University and Research, through Research Grant No. 20225ECXPP (to M.B., F.I, C.T. \u0026amp; S.S.) to study the impact of movement, action, and touch on memory.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eConceptualization \u0026ndash; Development of the main research ideas and overall study goals: S.S and C.T.Data curation \u0026ndash; Management, cleaning, and annotation of the dataset: I.N.R.Formal analysis \u0026ndash; Application of statistical and analytical techniques for data analysis: F.I. and I.N.R.Funding acquisition \u0026ndash; Securing financial support for the project: M.B.Investigation \u0026ndash; Execution of the research procedures, including data collection and experimental work: I.N.R. and A.S. Methodology \u0026ndash; Development and refinement of the study\u0026rsquo;s methodological approach and models: F.I. and T.L.Software \u0026ndash; Programming, implementation, and testing of software and algorithms used in the study: T.L. and I.N.R.Supervision \u0026ndash; Oversight of the research process, including guidance and mentorship: M.B. and S.S.Validation \u0026ndash; Verification of analyses, replication checks, and confirmation of findings: S.S., F.I. and I.N.R.Visualization \u0026ndash; Preparation and presentation of figures and other visual materials: I.N.R.Writing \u0026ndash; original draft \u0026ndash; Writing of the initial manuscript draft: S.S. and I.N.R.Writing \u0026ndash; review and editing \u0026ndash; Critical revision and editing of the manuscript throughout all stages: S.S., I.N.R., F.I., M.B., T.L., A.S. and C.T.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eWe thank the following students for their help during the experimental sessions: Mariangela De Angelis, Aliona Birda, Gaetano Manica, Constanza Martin, and all the participants.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe data reported in this paper are archived at the following link: https://h7.cl/1ftCo\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Notes\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data reported in this paper are archived at the following link: https://h7.cl/1ftCo\u003c/p\u003e\n\u003cp\u003eCorrespondence to this article should be addressed to Susanna Schmidt, Universit\u0026agrave; degli Studi di Torino, Dipartimento di Psicologia, Via Verdi, 10, 10124 Turin, Italy. 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C., Caldwell, T. L., Calin-Jageman, R. J., Capaldi, C. A., Carfagno, N. S., Chasten, K. T., Cleeremans, A., Connell, L., DeCicco, J. M., \u0026hellip; Zwaan, R. A. (2016). Registered Replication Report: Strack, Martin, \u0026amp; Stepper (1988). \u003cem\u003ePerspectives on Psychological Science\u003c/em\u003e, \u003cem\u003e11\u003c/em\u003e(6), 917\u0026ndash;928. https://doi.org/10.1177/1745691616674458\u003c/p\u003e"},{"header":"Footnotes","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003e Preliminary results of Experiment 1 involving 26 out of 60 participants have been accepted for publication as research notes in the Giornale Italiano di Psicologia (Ras et al, in press).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"psychological-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"prpf","sideBox":"Learn more about [Psychological Research](http://link.springer.com/journal/426)","snPcode":"426","submissionUrl":"https://submission.nature.com/new-submission/426/3","title":"Psychological Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"facial feedback hypothesis, perception, memory, embodied emotion, emotional facial stimuli","lastPublishedDoi":"10.21203/rs.3.rs-8252710/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8252710/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eOur investigation explores the facial feedback hypothesis in relation to the perception and memory of emotional faces. In Experiment 1, participants rated the valence of angry, neutral, and happy faces while vertically holding a pen either between their teeth (smile-facilitating condition) or between their lips (smile-inhibiting condition). Results indicated that participants in the teeth condition rated happy faces more positively than participants in the lips condition, while no difference was found for angry and neutral faces. Moreover, reaction times for the evaluation of angry faces were longer than the ones for neutral and happy faces. Experiment 2 assessed long-term memory for angry, neutral, and happy faces. During encoding, participants saw the same faces as in Experiment 1. During recognition, they had to select the previously seen faces from a set containing target and filler faces while holding a pen either between their teeth or their lips. Results indicated no significant differences both for accuracy and recognition times between the two groups. The results revealed better memory performance for angry faces compared to neutral and happy ones, regardless of the pen-in-mouth condition. Taken together, these findings suggest that this procedure influences the perception of happy faces only, while the manipulation had no significant effect on memory. Interestingly, angry faces required more time to be evaluated in Experiment 1 and were recognized more accurately in Experiment 2.\u003c/p\u003e","manuscriptTitle":"Facial Feedback on the Perception and Memory for Emotional Faces","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-05 13:46:43","doi":"10.21203/rs.3.rs-8252710/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-01-08T07:31:33+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-01-08T02:36:18+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-01-05T14:33:24+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"338182150755026808008122509046958287773","date":"2025-12-05T00:27:35+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"209487479719606485330798241957611943508","date":"2025-12-04T17:00:23+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-12-02T13:18:05+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-12-02T12:17:30+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-12-02T04:46:04+00:00","index":"","fulltext":""},{"type":"submitted","content":"Psychological Research","date":"2025-12-01T16:39:54+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"psychological-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"prpf","sideBox":"Learn more about [Psychological Research](http://link.springer.com/journal/426)","snPcode":"426","submissionUrl":"https://submission.nature.com/new-submission/426/3","title":"Psychological Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"adbb1c26-5810-4c17-bc6e-e0fe4440fdd0","owner":[],"postedDate":"December 5th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-04-24T09:49:49+00:00","versionOfRecord":[],"versionCreatedAt":"2025-12-05 13:46:43","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8252710","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8252710","identity":"rs-8252710","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}