The organization of action representation and the interaction between the action and perception systems

Action representation is thought to rely on hierarchical processing, whereby action-related information is represented across different levels of abstraction. The visual processing of human actions is subserved by the Action Observation Network (AON), spanning separate anatomical areas. Rather than relying on a modular organization based on the segregation of action features, the AON organization may be based on distributed representations, overlapping across a wide expanse of the cortex and supporting a high-dimensional representational space. Coherently with modern perspectives of distributed interactive cortical systems, it has been proposed that the same representational systems are shared between action, perception, and higher-level cognitive functions; in this view, action and perception are interdependent systems characterized by reciprocal influences. In the first and second studies, we aimed to better characterize the organization of the AON at different levels of the action hierarchy by measuring brain hemodynamic activity and representational geometries during observation of transitive and intransitive gestures. In the third study, we propose a novel methodological and analytical framework aimed at investigating the interplay between action and perceptual processes during active perception; we tested the validity of the proposed approach by recording participants’ motor and perceptual behavior during a perceptual decision-making task and assessing the influence of motor control features on decision formation. The results of the first and the second study indicate that actions categories are not encoded in a segregated manner and that the same areas of the AON participate in the representations of multiple action features; moreover, the representational content of the AON is not constrained by xiv anatomical proximity, as anatomically distant regions shared similar information content. These findings support the notion that the AON relies on overlapping and distributed coding and may act as a unique representational space. In the third study, we established a link between motor and perceptual behavior, as changes in movement kinematics continuously tracked the decision formation process, and we revealed a significant contribution of grip force to perceptual decisions. These results support the validity of the proposed approach in exploring the relationship between patterns of motor behavior and decision processes and the neurophysiological correlates underlying decision-making mechanisms.