Affordance matching predictively shapes the perceptual representation of others’ ongoing actions

Recent predictive processing models argue that action understanding is a predictive process, in which goal inferences are constantly tested by comparing predictions of forthcoming behaviour against the actual perceptual input. In a recent series of studies, we showed that these predictions can be visible as a subtle shift in perceptual action judgments towards these inferred goals. Here we test whether this perceptual shift occurs even when goals are not explicitly given but have to be derived implicitly from the unfolding action kinematics. In two experiments, participants watched an actor reach towards a large object and a small object forming either a whole hand power grip or a precision grip. During its course, the hand suddenly disappeared, and participants made perceptual judgments about the last seen position on a touch screen. As predicted, judgments were consistently biased towards apparent action targets, such that power grips were perceived closer to large objects and precision grips closer to small objects, even if the actual kinematics were the same. Strikingly, perceptual shifts were independent of participants’ explicit goal judgments, and were of equal size when action goals were explicitly judged in each trial (Experiment 1) or not judged (Experiment 2). Moreover, across trials and across participants, explicit goal judgments and perceptual shifts were uncorrelated. This provides evidence, for the first time, that people make on-line adjustments of predicted actions based on the match between hand grip and object goals, distorting the perceptual representation of the action. These distortions may not reflect high-level goal assumptions, but emerge from relatively low-level processing of kinematic features within the perceptual system