What Are They Up To? The Role of Sensory Evidence and Prior Knowledge in Action Understanding

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

doi:10.1371/journal.pone.0017133

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 stems 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, we conducted four behavioural experiments in which participants were instructed to identify different types of intention: basic 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 varied (1) the amount of visual information available from the action scene and (2) participant's prior expectations concerning the intention that was more likely to be accomplished. First, we showed that intentional judgments depend on a consistent interaction between visual information and participant's prior expectations. Moreover, we demonstrated that this interaction varied according to the type of intention to be inferred, with participant's priors rather than perceptual evidence exerting a greater effect on the inference of social and superordinate intentions. 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.

Highlights

Intentional inference: perceptual information and top-down prior knowledgeExplaining or predicting the behaviour of our conspecifics requires the ability to properly appreciate the causes that motivate it
These expectations are derived from prior knowledge that may originate from the past experience of the viewer, from her intuitive theories [7,8], or reputational knowledge [9,10], as well as from contextual information surrounding the action scene [5,11]
In the baseline session, there were no significant differences among hits and reaction times (RTs) between the ‘likely intention’ and the ‘unlikely intention’, indicating that prior to biasing participants, there was no a priori bias towards one intention rather than another

Summary

Introduction

Intentional inference: perceptual information and top-down prior knowledgeExplaining or predicting the behaviour of our conspecifics requires the ability to properly appreciate the causes that motivate it. One way to solve this problem is to assume that this space of possible intentions is further constrained by the observer’s prior expectations These expectations are derived from prior knowledge that may originate from the past experience of the viewer (through expertise: [4,5]; or learning of statistical regularities: [6]), from her intuitive theories [7,8], or reputational knowledge [9,10], as well as from contextual information surrounding the action scene [5,11]. It makes possible inductive inference about the agent’s intentions, even in cases of noisy signals or incomplete data [13,14,15]

Methods

Results

Discussion

Conclusion