Organization of affordance processing in perception-action systems.

Introduction: Visual tool processing (VTP), functional grasp planning (FGP) and tool use pantomimes (TUP) are typically associated with left-lateralized cerebral mechanisms. Yet, specific relationships between their neural underpinnings and levels of processing involved are largely unknown. We studied whether similar cerebral asymmetries are observed in the three tasks across different handedness groups, and how they link to the three-action system (3AS) model. Methods: Sixty-two participants (34 non-righthanders) were scanned with fMRI. The same stimuli-12 tools and 12 control objects-were utilized in each task. Whole-brain voxel wise analyses were performed and laterality indices (LIs) calculated in critical regions of interest (ROIs) for the assessment of hemispheric dominance, links to handedness, and global between-task relationships. Results: Depending on the region, VTP was not left lateralized, unlike FGP and TUP. The contributions of the dorso-dorsal, ventro-dorsal, and ventral stream-in 3AS associated with affordance processing, mechanical, and function knowledge-were contingent on task and phenotypic complexity. LIs for VTP and TUP, and FGP and TUP were significantly correlated. VTP and FGP LIs, unlike the TUP LIs, were linked to handedness. The global between-task relationships were contingent on processing levels. Discussion: These findings shed new light on affordance encoding, and their ability to automatically invoke neurocognitive mechanisms underlying tool functions and related actions. Future models should consider the mechanisms shared, the levels of processing involved, and their contingence on task complexity, individual variability, and sensorimotor integration, regardless of the involvement of manual responses.