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Action observation is central to human social interaction.It allows people to derive what mental states drive others' behaviour and coordinate (and compete) effectively with them. Although previous accounts have conceptualised this ability in terms of bottom-up (motoric or conceptual) matching processes, more recent evidence suggests that such mechanisms cannot account for the complexity and uncertainty of the sensory input, even in cases where computations should be much simpler (i.e., low-level vision). It has therefore been argued that perception in general, and social perception in particular, is better described as a process of top-down hypothesis testing. In such models, any assumption about others-their goals, attitudes, and beliefs-is translated into predictions of expected sensory input and compared with incoming stimulation. This allows perception and action to be based on these expectations or-in case of a mismatch-for one's prior assumptions to be revised until they are better aligned with the individual's behaviour. This article will give a (selective) review of recent research from experimental psychology and (social) neuroscience that supports such views, discuss the relevant underlying models, and current gaps in research. In particular, it will argue that much headway can be made when current research on predictive social perception is integrated with classic findings from social psychology, which have already shown striking effects of prior knowledge on the processing of other people's behaviour. | INTRODUCTIONUnderstanding other people's behaviour is central to human social interaction. It allows people to derive the goals, attitudes, and beliefs guiding others' actions (Hamilton, 2009), learn which outcomes these actions will produce (Ikegami & Ganesh, 2014;Knoblich & Flach, 2001), and respond appropriately to them, often in an anticipatory manner (e.g., in joint action, Sebanz, Bekkering, & Knoblich, 2006;Sebanz & Knoblich, 2009 Since the discovery of mirror neurons (Di Pellegrino, Fadiga, Fogassi, Gallese, & Rizzolatti, 1992;Fogassi et al., 2005; in humans, see Mukamel, Ekstrom, Kaplan, Iacoboni, & Fried, 2010;Oosterhof, Tipper, & Downing, 2013), action understanding has typically been conceptualised as a bottom-up process. Observed actions-typically conceptualised as simple goaldirected behaviours such as reaching and grasping or simple object use-are first represented in perceptual structures of the brain, then "directly matched" against actions the observer could carry out themselves, which then activates goals and other states associated with the action, allowing it to be understood without "inferential processing" or "backwards projections" (e.g., Rizzolatti & Sinigaglia, 2010;Rizzolatti, Cattaneo, Fabbri-Destro & Rozzi, 2014). These ideas have been widely successful and led to the characterisation of the motor system as a "tuning fork," which passively "resonates" with observed actions (for discussion, see Uithol, van Rooij, Bekkering, & Haselager, 2011;Jacob, 2008), or fo...

Predictions allow humans to manage uncertainties within social interactions. Here, we investigate how explicit and implicit person models–how different people behave in different situations–shape these predictions. In a novel action identification task, participants judged whether actors interacted with or withdrew from objects. In two experiments, we manipulated, unbeknownst to participants, the two actors action likelihoods across situations, such that one actor typically interacted with one object and withdrew from the other, while the other actor showed the opposite behaviour. In Experiment 2, participants additionally received explicit information about the two individuals that either matched or mismatched their actual behaviours. The data revealed direct but dissociable effects of both kinds of person information on action identification. Implicit action likelihoods affected response times, speeding up the identification of typical relative to atypical actions, irrespective of the explicit knowledge about the individual’s behaviour. Explicit person knowledge, in contrast, affected error rates, causing participants to respond according to expectations instead of observed behaviour, even when they were aware that the explicit information might not be valid. Together, the data show that internal models of others’ behaviour are routinely re-activated during action observation. They provide first evidence of a person-specific social anticipation system, which predicts forthcoming actions from both explicit information and an individuals’ prior behaviour in a situation. These data link action observation to recent models of predictive coding in the non-social domain where similar dissociations between implicit effects on stimulus identification and explicit behavioural wagers have been reported.

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