Shared and individual thresholds for social signal detection

To the human eye, social cues are omnipresent. The recently proposed third visual stream highlights the role of motion in detecting social signals (Pitcher and Ungerleider, 2021, TICS). Parameters like the directness of a chase (“chase subtlety”; Gao et al., 2009, Cognitive Psychology) and speed can be vital cues indicating the presence and nature of social interactions. We hypothesized that social perception is driven by both shared and individual thresholds of these motion parameters – leading to group-level similarities and individual differences in percepts, respectively. We studied two types of dynamic interactions involving circles (“agents”) – one agent pursuing the other (Study1), and two agents intermittently coming into contact for a friendly or aggressive interaction (Study2) – by systematically varying the chase subtlety (Study1) and the speed at which agents charged toward each other (Study2). To control for baseline perceptual biases, we also included additional videos comprising two agents wandering randomly. Using continuous scales, individuals indicated how social an interaction was (Study1; three batches, total n=608), and what type of interaction they perceived on a play-fight spectrum (Study2; n=199). Participants also filled out trait questionnaires. We found that social perception decreased with increasing chase subtleties in all three batches of Study1 (LMEM; b<–0.25; p<1e-12). In Study2, interactions were perceived as more aggressive as the charging speed increased (LMEM; b=0.23; p<1e-43). Individuals who have stronger beliefs about the world being an interactive place perceived the videos of agents wandering as more social (Spearman r>.16; p<.02 in all three batches). Lower social ratings may also be associated with higher social skill deficits (Spearman r<–.13, p<.06). Our work shows that strong group-level social percepts (things that “everyone” sees) can result from varying simple motion parameters, and that individual differences are influenced by our beliefs about the world and general social skills.