Space and opportunity for action: investigating affordance across the extrapersonal and peripersonal spaces

Introduction: Perception of space is intertwined with the capacity of shaping action. However, their relationship in different spatial sectors remains largely unexplored. Here, we investigate macro- and micro-affordances within extra-personal (EPS) and peri-personal (PPS) spaces to confirm that visual perceptions evoke expected motor effects and test whether a relationship exists between macro- and micro-affordances. Methods: Healthy right-handed volunteers underwent a macro-affordance task (foot-related action in response to isolated objects or environmental layouts at different EPS distances) and a micro-affordance task (pantomime of a precision grip of a mug in four conditions: congruent-near and incongruent-near within PPS; congruent-far and incongruent-far within EPS). Two perceptual tasks provided thresholds: near-far EPS Judgment’s Transition Threshold (JTT) and Visual Reachability Judgment (VRJ), related to macro- and micro-affordances, respectively. Results: In 33 subjects, shorter foot-related response times were observed during conditions of far vs. near EPS, especially in layout conditions (mean±SD 1171.14±168.85 vs. 1184.11±160.19, p <0.05). Response times in layout conditions negatively correlated with descendant JTT (r=-0.44 p=0.009), i.e., the further the EPS threshold, the faster the step was initiated. There was a significant congruency by distance interaction (p<0.01), i.e., a congruency effect only for near/PPS stimuli. No significant correlations were observed between macro- and micro-affordances nor between near EPS and PPS extension (p>0.5). Conclusions: Perception and action are linked, with the perception of object position and distant environment enhancing action in PPS and EPS, respectively. Macro- and micro-affordances appear to be independent from each other at an individual level, suggesting distinct neurocognitive substrates for PPS and EPS.