The "social" and "interpersonal" body in spatial cognition. The role of agency and interagency.

In order to interact effectively, we need to represent our action as produced by human beings. According to direct access theories, the first steps of visual information processing offer us an informed direct grasp of the situation, especially when social and interpersonal components are implicated. Biological system detection may be the gateway of such smart processes and then may influence initial stages of perception fostering adaptive social behaviour. To investigate early neural correlates of human agency detection in ecological situations with more high or low social impact, we compared scenes showing a human versus artificial agent interacting with a human agent. Twenty volunteers participated in the study. They were asked to observe dynamic visual stimuli showing realistic interactions. ERP (event-related potentials) were recorded. Each stimulus depicted an arm executing a gesture addressed to a human agent. Visual features of the arm were manipulated: in half of trials, it was real; in other trials, it was deprived of some details and transformed in a statue-like arm. EEG morphological analysis revealed an early negative deflection peaking at about 155 ms. Peak amplitude data have been statistically analysed by repeated-measures ANOVAs. It was found that the peak was ampler in the left inferior posterior region when the gesturing arm was human. The early negative deflection, N150, which we found to be different between the human and artificial conditions, is presumably associated with human agency detection in high interpersonal context.