The role of optic flow on reactive brain processing in cognitive tasks during locomotion

: Perception and action share neural resources that must be flexibly allocated across simultaneous tasks. In this context, the optic flow provides key visual input during locomotion and may interact with concurrent cognitive processing. This study aimed to: 1) examine how walking modulates event-related potential (ERP) components linked to visual, attentional, and sensorimotor processes evoked by a concomitant cognitive task; 2) relate neural changes to behavior; 3) test whether optic flow modifies these locomotion effects; and 4) extend previous findings on anticipatory brain processing to post-stimulus activity. To these aims, forty participants performed a visual discrimination task under four conditions that manipulated locomotion (walking vs. standing) and visual stimulation (with vs. without optic flow). Behavioral measures (response time (RT), accuracy, RT variability) and ERP components indexing distinct brain processing stages were recorded. Behaviorally, walking improved performance by increasing accuracy and reducing RT variability, while optic flow reduced accuracy without affecting RT. At the brain level, walking decreased the prefrontal N1 (pN1), indicating lower visual awareness, but increased the N1 (enhanced visual attention). Walking with the optic flow also increased the prefrontal P1 (pP1), indicating greater sensorimotor awareness. The presence of the optic flow independently reduced P1 (associated with early visual processing) and increased the pN1 and the N1. The P3 varied only with stimulus type, indicating no walking or optic flow effects on post-perceptual evaluation. Overall, walking facilitated early cognitive processing, whereas the optic flow added sensory-attentional load, reducing accuracy via competition for visual resources. These results support multiple-resource allocation dual-task theories, highlighting how ecological multisensory environments may dynamically reallocate cognitive resources and shape neural processing during action. In addition, present data can be used to design immersive environments, motor-cognitive dual-task training, and real-world cognition studies.