Etude chez le sujet sain -
What are they up to? The role of sensory evidence and prior knowledge in action understanding

Valerian Chambon, Philippe Domenech, Elisabeth Pacherie, Etienne Koechlin, Pierre Baraduc and Chlöé Farrer

(soumis)

Abstract

Explaining or predicting the behaviour of our conspecifics requires the ability to infer the intentions that motivate it. Such inferences are assumed to rely on two types of information: (1) the sensory information conveyed by movement kinematics and (2) the observer’s prior expectations – acquired from past experience or derived from prior knowledge. However, the respective contribution of these two sources of information is still controversial. This controversy could stem in part from the fact that “intention” is an umbrella term that may embrace various sub-types each being assigned different scopes and targets. We hypothesized that variations in the scope and target of intentions may account for variations in the contribution of visual kinematics and prior knowledge to the intention inference process. To test this hypothesis 4 behavioural experiments were conducted in which participants were instructed to identify different types of intention: motor intentions (i.e. simple goal of a motor act), superordinate intentions (i.e. general goal of a sequence of motor acts), or social intentions (i.e. intentions accomplished in a context of reciprocal interaction). For each of the above-mentioned intentions, we also varied (1) the amount of visual information available from the action scene and (2) participant’s prior expectations reflecting probability of achievement of different intentions. First, we showed that intentional judgments depend on a consistent interaction between visual information and participants’ prior expectations. Crucially, this interaction varies according to the type of intention to be inferred, with participant’s priors exerting a greater effect on the judgment of social and superordinate intentions, at the expense of sensory evidence. The results are discussed by appealing to the specific properties of each type of intention considered and further interpreted in the light of a hierarchical model of action representation.

Keywords: Intention recognition; Sensory evidence; Prior knowledge; Bayesian inference; Social interaction.