Affordance Matching Predictively Shapes the Perceptual Representation of Others’ Ongoing Actions

Predictive processing accounts of social perception argue that action observation is a predictive process, in which inferences about others’ goals are tested against the perceptual input, inducing a subtle perceptual confirmation bias that distorts observed action kinematics toward the inferred goals. Here we test whether such biases are induced even when goals are not explicitly given but have to be derived from the unfolding action kinematics. In 2 experiments, participants briefly saw an actor reach ambiguously toward a large object and a small object, with either a whole-hand power grip or an index-finger and thumb precision grip. During its course, the hand suddenly disappeared, and participants reported its last seen position on a touch-screen. As predicted, judgments were consistently biased toward apparent action targets, such that power grips were perceived closer to large objects and precision grips closer to small objects, even if the reach kinematics were identical. Strikingly, these biases were independent of participants’ explicit goal judgments. They were of equal size when action goals had to be explicitly derived in each trial (Experiment 1) or not (Experiment 2) and, across trials and across participants, explicit judgments and perceptual biases were uncorrelated. This provides evidence, for the first time, that people make online adjustments of observed actions based on the match between hand grip and object goals, distorting their perceptual representation toward implied goals. These distortions may not reflect high-level goal assumptions, but emerge from relatively low-level processing of kinematic features within the perceptual system.
Public Significance Statement This study shows that our perceptions of others’ actions are biased by which object we expect the person to reach for. Hands that form a large grip are seen to reach closer to large objects than they really were, and hands that form a small grip are seen to reach closer to small objects. These action expectations are generated during the ongoing observation of other’s actions, as grip information becomes available, and is matched to the size of objects within reaching distance. These expectations distort the perception of the action, and are independent from explicit action evaluations, suggesting that they emerge from processes within the perceptual system itself, rather than from more sophisticated, high-level reasoning about the actor’s goals.