Enhanced olfactory performance in deaf Dalmatians: evidence for neurosensory compensation?

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Mathieu Magnin, Emilie Boulard, Géraldine Lucchi, Karine Gourrat, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7937961/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Congenital deafness in dogs arises early in life and may lead to compensatory neuroplastic changes involving other sensory modalities. This study assessed whether deaf dogs exhibit enhanced olfactory performance compared to their hearing counterparts. A food search task conducted in a complex indoor environment was used to evaluate olfactory ability. Dogs were required to locate a single hidden kibble across progressively challenging hiding locations. After a learning phase, the evaluation focused on the most difficult conditions, where the kibble was neither visible nor accessible without olfactory guidance. Six purebred Dalmatians (three deaf, three hearing) were initially enrolled; two were excluded due to dropout or lack of motivation. All remaining dogs completed six training sessions before evaluation. Performance was measured as search speed (distance divided by search time), and group differences were analyzed using linear mixed-effects models. Deaf dogs demonstrated significantly higher search speeds than hearing dogs under the most demanding conditions (kibble hidden at a height), but not under simpler ones. No significant effect of time since last meal or interval between sessions was observed. These preliminary findings suggest a potential enhancement of olfactory performance in deaf dogs, possibly as a compensatory response to early auditory deprivation. Congenital deafness Dalmatia Olfaction Olfactory search task Sensory compensation Figures Figure 1 Figure 2 Introduction Sensory deprivation does not necessarily diminish overall perceptual capabilities. In many cases, neural plasticity enables the brain to reorganize in ways that enhance the remaining senses, a process known as compensatory plasticity. This reorganization frequently involves cross-modal plasticity, wherein cortical regions originally devoted to the deprived sense become responsive to inputs from other sensory modalities. Such adaptive changes are particularly pronounced when sensory loss occurs early in development (Lazzouni and Lepore 2014 ). Congenital deafness is relatively prevalent in Dalmatians and typically results from the degeneration of cochlear hair cells within the first month of life (Lewis et al. 2020 ). The early onset of this auditory deprivation makes it a compelling model for investigating potential sensory compensation. Given the central importance of olfaction in canine behavior and cognition, it is plausible that cross-modal plasticity in deaf dogs might involve enhanced olfactory abilities (Kokocińska-Kusiak et al. 2021 ). In the present study, we investigated this hypothesis by comparing the olfactory performance of congenitally deaf and hearing Dalmatians in a controlled food search task. We hypothesized that deaf individuals would locate hidden food more rapidly and with greater efficiency, consistent with the hypothesis of sensory compensation. Materials and methods This study was approved by the institutional animal ethics committee (authorization no. 2371). Subjects Purebred Dalmatians aged between 1 and 6 years were recruited. Inclusion criteria required that dogs be either bilaterally deaf or bilaterally hearing, as determined by Brainstem Auditory Evoked Response testing. Owners were required to commit to bringing their dogs to the research facility once per month. Exclusion criteria included behavioral problems, poor cooperation during olfactory testing, current illness, or ongoing medical treatment. Eligible dogs were assigned to either a "deaf" or "hearing" group based on auditory status. Odor stimulus standardization To ensure consistency in the odor stimuli used across trials, a single dog kibble from “Royal Canin Educ Low Calories” (Royal Canin, Aimargues, France) was used as the olfactory target (the composition of the kibble is presented in Supplementary Data S1). All bags containing dog kibbles were stored under identical conditions, in accordance with the manufacturer's recommendations. A new kibble bag was opened for each testing session. Chromatograms were overlayed across five kibbles from the same bag and two kibbles from three distinct bags representing different production batches. Analyses were performed by the Chemosens Laboratory (INRAE, Dijon, France – see details in Supplementary Data S1). Experimental setup Olfactory performance was assessed in a complex indoor setting (library of the research facility; see Supplementary S1). A single kibble was hidden in one of several pre-defined locations. The experiment was divided into two phases: a learning phase and an evaluation phase. Learning phase The learning phase aimed to familiarize dogs with the environment and the task. Five types of hiding spots were used, ranging in difficulty from 1 (visible on the floor near the entrance) to 5 (hidden at a height and not visible). Each learning session comprised five trials, with hiding spot locations following a predetermined randomization scheme (see Supplementary S1). Before testing began, dogs were allowed to freely explore the room without any food present to become accustomed to ambient odors and spatial layout. During each trial, dogs exited the room while the kibble was hidden. Upon re-entry, the search command was given verbally (“search”) for hearing dogs or via visual cue for deaf dogs. Each dog was expected to find one kibble per trial, with five trials per session. Progression to the next session required: Demonstrated motivation (active search behavior), Absence of calming signals (e.g., yawning, lip licking), Completion of all five searches. If a dog did not meet these criteria, the session was repeated. Once each hiding difficulty level had been completed successfully, dogs progressed to the evaluation phase. Evaluation phase During evaluation, only the most difficult hiding conditions (types 4 and 5) were used. Type 4 involved hidden kibble placed on the floor and out of view, while type 5 involved hidden kibble placed at a height. Each dog completed 20 trials (10 per hiding type) across four sessions. For each trial, the following variables were recorded: Hiding spot type, Outcome (success or failure), Search time (in seconds), Distance from door to hiding location (in meters, measured by laser), Time since last meal, Time elapsed since previous session. Search performance was quantified by calculating search speed (m/s) as: Speed = Distance to kibble / Search time Higher values indicated faster and more efficient performance. Statistical analysis Data are presented as median values with interquartile ranges (Q1–Q3). Separate linear mixed-effects models were fitted to assess differences in search speed between deaf and hearing dogs for each hiding spot type (type 4 and type 5). In each model, search speed was treated as the dependent variable, group (deaf vs. hearing) was a fixed effect, and dog identity was a random effect to account for repeated measures within subjects. Model assumptions were verified via inspection of residual plots for normality and homoscedasticity. Pearson correlation analyses were conducted to assess whether search speed was influenced by either the time since the last meal or the interval since the previous session. All analyses were conducted using RStudio (v. 2023.09.1) with the packages lme4 and ggplot2. Results Gas chromatography–mass spectrometry analyses confirmed the consistency of the olfactory stimulus. Chromatograms of kibbles from the same bag or batch were highly similar (Supplementary S2). Moderate differences in the concentration of some volatile compounds were observed between batches. However, the qualitative similarity in the odor spectra across samples suggests that these minor variations were unlikely to have influenced dogs' performance during the search tasks. A total of six Dalmatians were initially enrolled in the study (three deaf and three hearing). Two dogs were excluded: one deaf dog was withdrawn due to logistical constraints (owners relocated), and one hearing dog was excluded due to repeated signs of stress and low motivation during the learning phase. Individual characteristics of the remaining subjects are presented in Supplementary Table S3. Boxplots display the distribution of search speeds (m/s) for each dog, grouped by hearing status. Blue boxplots correspond to hearing dogs; green boxplots correspond to deaf dogs. Colored dots represent individual trials, with orange indicating trials involving type 4 hiding spots (hidden on the floor) and grey indicating type 5 hiding spots (hidden at a height). Each point reflects one search trial. All included dogs completed six learning sessions prior to entering the evaluation phase. Descriptive results from the evaluation phase are presented in Fig. 1 . Across all hiding spot types, the median search speed in the hearing group was 0.16 m/s (0.10–0.32). For type 4 hiding spots, the median speed was 0.20 m/s (0.14–0.38), and for type 5, it was 0.10 m/s (0.09–0.17). In the deaf group, the overall median speed was 0.26 m/s (0.13–0.38). For type 4 hiding spots, median speed was 0.27 m/s (0.13–0.38), and for type 5, 0.25 m/s (0.17–0.36). Linear mixed-effects modeling revealed that deaf dogs exhibited significantly higher search speeds than hearing dogs for type 5 hiding spots (estimate: 0.13 m/s; 95% CI: 0.03–0.23; Table 1 ). No significant group difference was found for type 4 hiding spots (estimate: 0.01 m/s; 95% CI: − 0.09–0.12). Table 1 Effect of auditory status (deaf vs. hearing) on search speed across hiding spot types. Type of the hiding spot Dependent variable Independent variable Estimate 95% confidence interval 4 Speed (m/s) Intercept 0.27 0.19; 0.34 Deaf group 0.01 -0.09; 0.12 5 Speed (m/s) Intercept 0.16 0.08; 0.23 Deaf group 0.13 0.03; 0.23 Results from two independent linear mixed-effects models evaluating the effect of group (deaf vs. hearing) on search speed (m/s), conducted separately for each hiding spot type (type 4: hidden on the floor; type 5: hidden at a height). For type 4, no significant difference was observed between groups. For type 5, deaf dogs exhibited significantly higher search speeds than hearing dogs, as indicated by the positive estimate and the 95% confidence interval not including zero No significant correlations were observed between search speed and either the time since the last meal or the time elapsed since the previous session (Fig. 2 ; Supplementary S4). This lack of association held true for the entire sample as well as within each group independently. Scatter plots depict individual search speeds (m/s) as a function of (A) the time elapsed since the previous session (in days), and (B) the time since the last meal (in minutes), for deaf (green) and hearing (blue) dogs. No consistent relationship was observed between search speed and either variable in the different groups. Discussion This study investigated whether Dalmatians with congenital deafness display enhanced olfactory abilities compared to hearing conspecifics. Using a controlled food-search paradigm in a complex indoor setting, we observed that deaf dogs outperformed hearing dogs under the most challenging olfactory conditions—specifically when the food reward was both hidden and elevated. No group differences were noted under simpler task settings. Furthermore, performance was unaffected by either the time since the last meal or the interval between testing sessions. To our knowledge, this is the first study to explore potential sensory compensation in congenitally deaf dogs. Evidence from other species supports the notion of compensatory plasticity following early sensory deprivation. In cats, early-onset deafness has been associated with enhanced visual motion detection and peripheral attention, mediated by cross-modal recruitment of the auditory cortex (Lomber et al. 2010 ). Notably, such reorganization is functionally selective, favoring cortical regions whose original auditory role overlaps with the compensating modality. These findings suggest that cross-modal plasticity enhances function in a modality-specific and adaptive manner. In dogs, olfaction is a dominant sensory modality. With over 220 million olfactory receptors and a disproportionately large olfactory bulb, canines possess a highly developed chemosensory system (Kokocińska-Kusiak et al. 2021 ). The present results are thus consistent with the hypothesis that compensatory reorganization may reinforce an already prominent sense, particularly under ecologically demanding conditions. Findings in humans also support this interpretation. Landry et al. reported enhanced olfactory and trigeminal sensitivity in congenitally deaf individuals compared to hearing controls, using rigorous controls to isolate sensory performance from cognitive confounds (Landry et al. 2024 ). These results contrast with earlier studies that failed to detect such enhancements (Diekmann et al. 1994 ; Guducu et al. 2016 ), likely due to methodological limitations. The present canine data add to this literature by providing a comparative model in which ecological behaviors such as olfactory search can be objectively assessed. The absence of significant effects related to feeding interval or inter-session spacing was somewhat unexpected. Given that some sessions were spaced by several weeks, the stability of performance across time suggests robust learning and task retention. Similarly, the lack of modulation by hunger state may reflect the limited range of postprandial delays in this protocol. Since the dogs’ feeding routines remained regular, motivation levels were likely consistent across trials. Several limitations must be acknowledged. First, the small sample size restricts statistical power and generalizability. Recruitment challenges, especially for congenitally deaf Dalmatians, constrained study size. It is possible that factors such as sex, hormonal status (intact or neutered), and age may have influenced the kibble search speed. Unfortunately, due to the small sample size, we were unable to statistically assess the impact of these variables. Second, our focus on olfactory ability precluded exploration of compensation across other modalities, such as vision or tactile sensitivity. Including a multimodal assessment would provide a more comprehensive picture of cross-modal plasticity. Third, caution is warranted when interpreting results derived from linear mixed models in small samples. With only two individuals contributing repeated measures per group, assumptions regarding the distribution of random effects may not hold. Nonetheless, the combination of descriptive statistics, detailed graphical representation, and model output provides a transparent basis for interpretation. In conclusion, this exploratory study provides preliminary evidence that deaf Dalmatians may exhibit enhanced olfactory performance under demanding conditions. While performance did not differ under simpler settings, deaf dogs located hidden elevated food more rapidly than their hearing counterparts. These findings are consistent with the hypothesis of functional compensation following early auditory deprivation. Future studies with larger samples and multimodal designs are warranted. Declarations Conflict of interest : The authors declare that they have no conflict of interest. Ethical approval : All procedures involving animals were approved by the institutional ethics committee (approval number: 2371). AI declaration Minor language editing was performed using an AI-assisted tool (ChatGPT, OpenAI), under author supervision. Funding: This study was supported by a grant from the Société Centrale Canine - Agria . Author Contribution MM: Methodology, Formal analysis, Data curation, Writing – original draft, Writing – review & editing, Visualization, Supervision.EB: Methodology, Investigation, Writing – original draft, Visualization.GL: Investigation, Methodology, Writing – review & editingKG: Investigation, Methodology, Writing – review & editingCC: Conceptualization, Funding acquisition.JJT: Conceptualization, Methodology, Writing – review & editing, Supervision, Project administration, Funding acquisition.BF: Conceptualization, Methodology, Writing – review & editing, Supervision, Project administration, Funding acquisition. Data Availability The data that support the findings of this study are available from the corresponding author upon reasonable request. References Diekmann H, Walger M, von Wedel H (1994) [Sense of smell in deaf and blind patients]. HNO 42:264–269 Guducu C, Oniz A, Ikiz AO, Ozgoren M (2016) Chemosensory Function in Congenitally Blind or Deaf Teenagers. Chemosens Percept 9:8–13. https://doi.org/10.1007/s12078-015-9199-2 Kokocińska-Kusiak A, Woszczyło M, Zybala M et al (2021) Canine Olfaction: Physiology, Behavior, and Possibilities for Practical Applications. Anim Open Access J MDPI 11:2463. https://doi.org/10.3390/ani11082463 Landry C, Nazar R, Simon M et al (2024) Behavioural evidence for enhanced olfactory and trigeminal perception in congenital hearing loss. Eur J Neurosci 59:434–445. https://doi.org/10.1111/ejn.16216 Lazzouni L, Lepore F (2014) Compensatory plasticity: time matters. Front Hum Neurosci 8:340. https://doi.org/10.3389/fnhum.2014.00340 Lewis T, Freeman J, De Risio L (2020) Decline in prevalence of congenital sensorineural deafness in Dalmatian dogs in the United Kingdom. J Vet Intern Med 34:1524–1531. https://doi.org/10.1111/jvim.15776 Lomber SG, Meredith MA, Kral A (2010) Cross-modal plasticity in specific auditory cortices underlies visual compensations in the deaf. Nat Neurosci 13:1421–1427. https://doi.org/10.1038/nn.2653 Additional Declarations No competing interests reported. Supplementary Files Supplementarydata.docx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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2","display":"","copyAsset":false,"role":"figure","size":40215,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of session interval and feeding timing on olfactory search speed\u003c/p\u003e","description":"","filename":"Onlinefloatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-7937961/v1/603f46d26f87078de6980d45.png"},{"id":95526623,"identity":"85ea7788-d7d2-4664-b7cb-72ff053e55c9","added_by":"auto","created_at":"2025-11-10 10:07:26","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":538369,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7937961/v1/f3c856fa-341e-42ce-8697-5ce3f33e3492.pdf"},{"id":95297304,"identity":"c1ebf2ce-a505-4483-9431-eb6951d71ba2","added_by":"auto","created_at":"2025-11-06 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In many cases, neural plasticity enables the brain to reorganize in ways that enhance the remaining senses, a process known as compensatory plasticity. This reorganization frequently involves cross-modal plasticity, wherein cortical regions originally devoted to the deprived sense become responsive to inputs from other sensory modalities. Such adaptive changes are particularly pronounced when sensory loss occurs early in development (Lazzouni and Lepore \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eCongenital deafness is relatively prevalent in Dalmatians and typically results from the degeneration of cochlear hair cells within the first month of life (Lewis et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The early onset of this auditory deprivation makes it a compelling model for investigating potential sensory compensation. Given the central importance of olfaction in canine behavior and cognition, it is plausible that cross-modal plasticity in deaf dogs might involve enhanced olfactory abilities (Kokocińska-Kusiak et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eIn the present study, we investigated this hypothesis by comparing the olfactory performance of congenitally deaf and hearing Dalmatians in a controlled food search task. We hypothesized that deaf individuals would locate hidden food more rapidly and with greater efficiency, consistent with the hypothesis of sensory compensation.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cp\u003eThis study was approved by the institutional animal ethics committee (authorization no. 2371).\u003c/p\u003e\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003eSubjects\u003c/h2\u003e\u003cp\u003ePurebred Dalmatians aged between 1 and 6 years were recruited. Inclusion criteria required that dogs be either bilaterally deaf or bilaterally hearing, as determined by Brainstem Auditory Evoked Response testing. Owners were required to commit to bringing their dogs to the research facility once per month.\u003c/p\u003e\u003cp\u003eExclusion criteria included behavioral problems, poor cooperation during olfactory testing, current illness, or ongoing medical treatment. Eligible dogs were assigned to either a \"deaf\" or \"hearing\" group based on auditory status.\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eOdor stimulus standardization\u003c/h3\u003e\n\u003cp\u003eTo ensure consistency in the odor stimuli used across trials, a single dog kibble from \u0026ldquo;Royal Canin Educ Low Calories\u0026rdquo; (Royal Canin, Aimargues, France) was used as the olfactory target (the composition of the kibble is presented in Supplementary Data S1). All bags containing dog kibbles were stored under identical conditions, in accordance with the manufacturer's recommendations. A new kibble bag was opened for each testing session.\u003c/p\u003e\u003cp\u003eChromatograms were overlayed across five kibbles from the same bag and two kibbles from three distinct bags representing different production batches. Analyses were performed by the Chemosens Laboratory (INRAE, Dijon, France \u0026ndash; see details in Supplementary Data S1).\u003c/p\u003e\n\u003ch3\u003eExperimental setup\u003c/h3\u003e\n\u003cp\u003eOlfactory performance was assessed in a complex indoor setting (library of the research facility; see Supplementary S1). A single kibble was hidden in one of several pre-defined locations. The experiment was divided into two phases: a learning phase and an evaluation phase.\u003c/p\u003e\n\u003ch3\u003eLearning phase\u003c/h3\u003e\n\u003cp\u003eThe learning phase aimed to familiarize dogs with the environment and the task. Five types of hiding spots were used, ranging in difficulty from 1 (visible on the floor near the entrance) to 5 (hidden at a height and not visible). Each learning session comprised five trials, with hiding spot locations following a predetermined randomization scheme (see Supplementary S1).\u003c/p\u003e\u003cp\u003eBefore testing began, dogs were allowed to freely explore the room without any food present to become accustomed to ambient odors and spatial layout. During each trial, dogs exited the room while the kibble was hidden. Upon re-entry, the search command was given verbally (\u0026ldquo;search\u0026rdquo;) for hearing dogs or via visual cue for deaf dogs. Each dog was expected to find one kibble per trial, with five trials per session. Progression to the next session required:\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003eDemonstrated motivation (active search behavior),\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eAbsence of calming signals (e.g., yawning, lip licking),\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eCompletion of all five searches.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cp\u003eIf a dog did not meet these criteria, the session was repeated. Once each hiding difficulty level had been completed successfully, dogs progressed to the evaluation phase.\u003c/p\u003e\n\u003ch3\u003eEvaluation phase\u003c/h3\u003e\n\u003cp\u003eDuring evaluation, only the most difficult hiding conditions (types 4 and 5) were used. Type 4 involved hidden kibble placed on the floor and out of view, while type 5 involved hidden kibble placed at a height. Each dog completed 20 trials (10 per hiding type) across four sessions.\u003c/p\u003e\u003cp\u003eFor each trial, the following variables were recorded:\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003eHiding spot type,\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eOutcome (success or failure),\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eSearch time (in seconds),\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eDistance from door to hiding location (in meters, measured by laser),\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eTime since last meal,\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eTime elapsed since previous session.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cp\u003eSearch performance was quantified by calculating search speed (m/s) as:\u003c/p\u003e\u003cp\u003eSpeed\u0026thinsp;=\u0026thinsp;Distance to kibble / Search time\u003c/p\u003e\u003cp\u003eHigher values indicated faster and more efficient performance.\u003c/p\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003eStatistical analysis\u003c/h2\u003e\u003cp\u003eData are presented as median values with interquartile ranges (Q1\u0026ndash;Q3). Separate linear mixed-effects models were fitted to assess differences in search speed between deaf and hearing dogs for each hiding spot type (type 4 and type 5). In each model, search speed was treated as the dependent variable, group (deaf vs. hearing) was a fixed effect, and dog identity was a random effect to account for repeated measures within subjects. Model assumptions were verified via inspection of residual plots for normality and homoscedasticity. Pearson correlation analyses were conducted to assess whether search speed was influenced by either the time since the last meal or the interval since the previous session. All analyses were conducted using RStudio (v. 2023.09.1) with the packages lme4 and ggplot2.\u003c/p\u003e\u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eGas chromatography\u0026ndash;mass spectrometry analyses confirmed the consistency of the olfactory stimulus. Chromatograms of kibbles from the same bag or batch were highly similar (Supplementary S2). Moderate differences in the concentration of some volatile compounds were observed between batches. However, the qualitative similarity in the odor spectra across samples suggests that these minor variations were unlikely to have influenced dogs' performance during the search tasks.\u003c/p\u003e\u003cp\u003eA total of six Dalmatians were initially enrolled in the study (three deaf and three hearing). Two dogs were excluded: one deaf dog was withdrawn due to logistical constraints (owners relocated), and one hearing dog was excluded due to repeated signs of stress and low motivation during the learning phase. Individual characteristics of the remaining subjects are presented in Supplementary Table S3.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eBoxplots display the distribution of search speeds (m/s) for each dog, grouped by hearing status. Blue boxplots correspond to hearing dogs; green boxplots correspond to deaf dogs. Colored dots represent individual trials, with orange indicating trials involving type 4 hiding spots (hidden on the floor) and grey indicating type 5 hiding spots (hidden at a height). Each point reflects one search trial.\u003c/p\u003e\u003cp\u003eAll included dogs completed six learning sessions prior to entering the evaluation phase. Descriptive results from the evaluation phase are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\u003cp\u003eAcross all hiding spot types, the median search speed in the hearing group was 0.16 m/s (0.10\u0026ndash;0.32). For type 4 hiding spots, the median speed was 0.20 m/s (0.14\u0026ndash;0.38), and for type 5, it was 0.10 m/s (0.09\u0026ndash;0.17). In the deaf group, the overall median speed was 0.26 m/s (0.13\u0026ndash;0.38). For type 4 hiding spots, median speed was 0.27 m/s (0.13\u0026ndash;0.38), and for type 5, 0.25 m/s (0.17\u0026ndash;0.36).\u003c/p\u003e\u003cp\u003eLinear mixed-effects modeling revealed that deaf dogs exhibited significantly higher search speeds than hearing dogs for type 5 hiding spots (estimate: 0.13 m/s; 95% CI: 0.03\u0026ndash;0.23; Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). No significant group difference was found for type 4 hiding spots (estimate: 0.01 m/s; 95% CI: \u0026minus;\u0026thinsp;0.09\u0026ndash;0.12).\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eEffect of auditory status (deaf vs. hearing) on search speed across hiding spot types.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eType of the hiding spot\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eDependent variable\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eIndependent variable\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eEstimate\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003e95% confidence interval\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eSpeed (m/s)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eIntercept\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.27\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.19; 0.34\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eDeaf group\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e-0.09; 0.12\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eSpeed (m/s)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eIntercept\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.08; 0.23\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eDeaf group\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.13\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.03; 0.23\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003ctfoot\u003e\u003ctr\u003e\u003ctd colspan=\"5\"\u003eResults from two independent linear mixed-effects models evaluating the effect of group (deaf vs. hearing) on search speed (m/s), conducted separately for each hiding spot type (type 4: hidden on the floor; type 5: hidden at a height). For type 4, no significant difference was observed between groups. For type 5, deaf dogs exhibited significantly higher search speeds than hearing dogs, as indicated by the positive estimate and the 95% confidence interval not including zero\u003c/td\u003e\u003c/tr\u003e\u003c/tfoot\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eNo significant correlations were observed between search speed and either the time since the last meal or the time elapsed since the previous session (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e; Supplementary S4). This lack of association held true for the entire sample as well as within each group independently.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eScatter plots depict individual search speeds (m/s) as a function of (A) the time elapsed since the previous session (in days), and (B) the time since the last meal (in minutes), for deaf (green) and hearing (blue) dogs. No consistent relationship was observed between search speed and either variable in the different groups.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThis study investigated whether Dalmatians with congenital deafness display enhanced olfactory abilities compared to hearing conspecifics. Using a controlled food-search paradigm in a complex indoor setting, we observed that deaf dogs outperformed hearing dogs under the most challenging olfactory conditions\u0026mdash;specifically when the food reward was both hidden and elevated. No group differences were noted under simpler task settings. Furthermore, performance was unaffected by either the time since the last meal or the interval between testing sessions.\u003c/p\u003e\u003cp\u003eTo our knowledge, this is the first study to explore potential sensory compensation in congenitally deaf dogs. Evidence from other species supports the notion of compensatory plasticity following early sensory deprivation. In cats, early-onset deafness has been associated with enhanced visual motion detection and peripheral attention, mediated by cross-modal recruitment of the auditory cortex (Lomber et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). Notably, such reorganization is functionally selective, favoring cortical regions whose original auditory role overlaps with the compensating modality. These findings suggest that cross-modal plasticity enhances function in a modality-specific and adaptive manner. In dogs, olfaction is a dominant sensory modality. With over 220\u0026nbsp;million olfactory receptors and a disproportionately large olfactory bulb, canines possess a highly developed chemosensory system (Kokocińska-Kusiak et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The present results are thus consistent with the hypothesis that compensatory reorganization may reinforce an already prominent sense, particularly under ecologically demanding conditions.\u003c/p\u003e\u003cp\u003eFindings in humans also support this interpretation. Landry et al. reported enhanced olfactory and trigeminal sensitivity in congenitally deaf individuals compared to hearing controls, using rigorous controls to isolate sensory performance from cognitive confounds (Landry et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). These results contrast with earlier studies that failed to detect such enhancements (Diekmann et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1994\u003c/span\u003e; Guducu et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), likely due to methodological limitations. The present canine data add to this literature by providing a comparative model in which ecological behaviors such as olfactory search can be objectively assessed.\u003c/p\u003e\u003cp\u003eThe absence of significant effects related to feeding interval or inter-session spacing was somewhat unexpected. Given that some sessions were spaced by several weeks, the stability of performance across time suggests robust learning and task retention. Similarly, the lack of modulation by hunger state may reflect the limited range of postprandial delays in this protocol. Since the dogs\u0026rsquo; feeding routines remained regular, motivation levels were likely consistent across trials.\u003c/p\u003e\u003cp\u003eSeveral limitations must be acknowledged. First, the small sample size restricts statistical power and generalizability. Recruitment challenges, especially for congenitally deaf Dalmatians, constrained study size. It is possible that factors such as sex, hormonal status (intact or neutered), and age may have influenced the kibble search speed. Unfortunately, due to the small sample size, we were unable to statistically assess the impact of these variables. Second, our focus on olfactory ability precluded exploration of compensation across other modalities, such as vision or tactile sensitivity. Including a multimodal assessment would provide a more comprehensive picture of cross-modal plasticity. Third, caution is warranted when interpreting results derived from linear mixed models in small samples. With only two individuals contributing repeated measures per group, assumptions regarding the distribution of random effects may not hold. Nonetheless, the combination of descriptive statistics, detailed graphical representation, and model output provides a transparent basis for interpretation.\u003c/p\u003e\u003cp\u003eIn conclusion, this exploratory study provides preliminary evidence that deaf Dalmatians may exhibit enhanced olfactory performance under demanding conditions. While performance did not differ under simpler settings, deaf dogs located hidden elevated food more rapidly than their hearing counterparts. These findings are consistent with the hypothesis of functional compensation following early auditory deprivation. Future studies with larger samples and multimodal designs are warranted.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003e\u003cb\u003eConflict of interest\u003c/b\u003e:\u003c/strong\u003e\u003cp\u003eThe authors declare that they have no conflict of interest.\u003c/p\u003e\u003c/p\u003e\u003cp\u003e\u003cstrong\u003e\u003cb\u003eEthical approval\u003c/b\u003e:\u003c/strong\u003e\u003cp\u003eAll procedures involving animals were approved by the institutional ethics committee (approval number: 2371).\u003c/p\u003e\u003c/p\u003e\u003cp\u003e\u003ch2\u003eAI declaration\u003c/h2\u003e\u003cp\u003eMinor language editing was performed using an AI-assisted tool (ChatGPT, OpenAI), under author supervision.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eFunding:\u003c/h2\u003e\u003cp\u003eThis study was supported by a grant from the \u003cem\u003eSoci\u0026eacute;t\u0026eacute; Centrale Canine\u003c/em\u003e - \u003cem\u003eAgria\u003c/em\u003e.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eMM: Methodology, Formal analysis, Data curation, Writing \u0026ndash; original draft, Writing \u0026ndash; review \u0026amp; editing, Visualization, Supervision.EB: Methodology, Investigation, Writing \u0026ndash; original draft, Visualization.GL: Investigation, Methodology, Writing \u0026ndash; review \u0026amp; editingKG: Investigation, Methodology, Writing \u0026ndash; review \u0026amp; editingCC: Conceptualization, Funding acquisition.JJT: Conceptualization, Methodology, Writing \u0026ndash; review \u0026amp; editing, Supervision, Project administration, Funding acquisition.BF: Conceptualization, Methodology, Writing \u0026ndash; review \u0026amp; editing, Supervision, Project administration, Funding acquisition.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe data that support the findings of this study are available from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eDiekmann H, Walger M, von Wedel H (1994) [Sense of smell in deaf and blind patients]. HNO 42:264\u0026ndash;269\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGuducu C, Oniz A, Ikiz AO, Ozgoren M (2016) Chemosensory Function in Congenitally Blind or Deaf Teenagers. Chemosens Percept 9:8\u0026ndash;13. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s12078-015-9199-2\u003c/span\u003e\u003cspan address=\"10.1007/s12078-015-9199-2\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKokocińska-Kusiak A, Woszczyło M, Zybala M et al (2021) Canine Olfaction: Physiology, Behavior, and Possibilities for Practical Applications. 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Nat Neurosci 13:1421\u0026ndash;1427. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1038/nn.2653\u003c/span\u003e\u003cspan address=\"10.1038/nn.2653\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Congenital deafness, Dalmatia, Olfaction, Olfactory search task, Sensory compensation","lastPublishedDoi":"10.21203/rs.3.rs-7937961/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7937961/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eCongenital deafness in dogs arises early in life and may lead to compensatory neuroplastic changes involving other sensory modalities. This study assessed whether deaf dogs exhibit enhanced olfactory performance compared to their hearing counterparts. A food search task conducted in a complex indoor environment was used to evaluate olfactory ability. Dogs were required to locate a single hidden kibble across progressively challenging hiding locations. After a learning phase, the evaluation focused on the most difficult conditions, where the kibble was neither visible nor accessible without olfactory guidance. Six purebred Dalmatians (three deaf, three hearing) were initially enrolled; two were excluded due to dropout or lack of motivation. All remaining dogs completed six training sessions before evaluation. Performance was measured as search speed (distance divided by search time), and group differences were analyzed using linear mixed-effects models. Deaf dogs demonstrated significantly higher search speeds than hearing dogs under the most demanding conditions (kibble hidden at a height), but not under simpler ones. No significant effect of time since last meal or interval between sessions was observed. These preliminary findings suggest a potential enhancement of olfactory performance in deaf dogs, possibly as a compensatory response to early auditory deprivation.\u003c/p\u003e","manuscriptTitle":"Enhanced olfactory performance in deaf Dalmatians: evidence for neurosensory compensation?","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-06 12:32:34","doi":"10.21203/rs.3.rs-7937961/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"8b98e535-b37c-4633-8a9a-962fe55f3f26","owner":[],"postedDate":"November 6th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-11-07T19:23:25+00:00","versionOfRecord":[],"versionCreatedAt":"2025-11-06 12:32:34","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7937961","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7937961","identity":"rs-7937961","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}