Facial emotion recognition in autistic adults with or without co-occurring attention-deficit/hyperactivity disorder: a preregistered study

People with autism or attention deficit/hyperactivity disorder (ADHD) take longer to recognise emotions associated with certain facial expressions. While this effect has been sufficiently documented, its specificity received less attention. Since both conditions lead to increased reaction times on a wide variety of tasks, it is unclear whether differences in responses are specific to emotion recognition or due to attenuations of more basic sensory or motor processes. Therefore, we pair the use of a sensitive morphing task assessing emotion discrimination threshold (EDT), i.e., how much information is needed to correctly recognise an emotion, with a control task measuring species discrimination threshold (SDT). We hypothesise specific increases of EDT in adults with ADHD or autism, and differences in gaze patterns, specifically in dwell times and number of saccades. We assess our hypotheses in autistic adults with (n = 23) and without co-occurring ADHD (n = 23), adults with ADHD (n = 24) and a comparison group of typically-developing adults (n = 24). Our data supports differences in facial emotion recognition between adults with ADHD or autism and the comparison group. Furthermore, an explorative sample of adults with co-occurrence of ADHD and autism performed comparable to adults with either autism or ADHD, suggesting that a co-occurrence is not associated with additive or interactive effects. Importantly, EDT was equivalent in adults with ADHD as well as autistic adults with or without co-occurring ADHD when including SDT in the model. Moreover, there were no differences between groups in terms of gaze patterns. Similar emotion discrimination thresholds in autistic adults with and without co-occurring ADHD suggest shared mechanisms in autism and ADHD influencing facial emotion recognition. Similar gaze patterns indicate that differences in facial emotion recognition are not due to differences in attention to facial landmarks or information gathering strategies.