Abstract
BACKGROUND: Humans form almost instantaneous impressions of everyone they encounter. These impressions set the first tone for how they approach and interact with others. Research on impression formation unveiled that impressions formed by autistic and non-autistic people are often less favourable when rating an autistic person. This effect is partly explainable by differences in motion dynamics. METHODS: In this preregistered study, we systematically assessed impressions formed by 27 autistic and 36 non-autistic comparison observers when watching videos showing silent interactions between either two non-autistic or between an autistic and a non-autistic person. We used an eye tracker to capture their gaze patterns while observing these interactions. Of each dyadic interaction, video vignettes with high and vignettes with low interpersonal synchrony of movement (IPS(mov)) were extracted using Motion Energy Analysis so that we could investigate the effects of interpersonal synchrony and diagnosis, respectively. RESULTS: Interactions were rated less favourably when the observed dyad included an autistic adult. Additionally, interactions showing low IPS(mov) were rated less favourably than interactions showing high IPS(mov), regardless of dyad type. Both autistic and comparison observers rated interactions of non-autistic dyads and high IPS(mov) interactions more favourably. Gaze patterns revealed differences between autistic and comparison observers, but no differences due to IPS(mov) or dyad type. Furthermore, dwell times to hands predicted ratings. LIMITATIONS: In this study, we investigated specific influences on impression formation, specifically interpersonal synchrony of movement and autism. There are many more potentially interesting aspects of individuals that impact impression formation, such as facial expressiveness, gaze behaviour and linguistic content of conversations, which should be investigated systematically and in a controlled fashion in future research. CONCLUSIONS: Extending research on autism and impression formation to dyadic interactions, this study reveals that motion dynamics play a role in how pleasant interactions are perceived. Autistic-involved interactions were rated lower, despite observers being unaware of the dyad type and only watching people's outlines. Future research should identify conversational aspects driving lower ratings of mixed dyads, potentially considering the effect of hand dwell times on ratings. Autistic and comparison observers showed different gaze patterns despite similar ratings, confirming distinct social information processing.