Gait kinematics dynamically tune optic flow motion-in-depth perception during human locomotion

Behavior generates continuous sensorimotor contingencies that the brain must process. In particular, locomotion produces optic flow, which is frequently noisy and ambiguous during navigation. Integrating non-visual self-motion signals can therefore provide a computational advantage to resolve this sensory uncertainty. To investigate this we developed a novel head-mounted 3D motion coherence paradigm. We found that walking dissociably alters perceptual sensitivity and bias for optic flow, dependent on stimulus speed. Rather than acting as a binary state change, these modulations scale dynamically with step frequency. While slow stepping impairs sensitivity to optic flow, fast stepping rescues this deficit. Simultaneously, higher step frequencies drive a progressive shift in perceptual bias, consistent with canceling expected self-generated flow. Our results indicate that optic flow perception during locomotion is modulated by active processes, encompassing both discrete behavioral state changes and continuous, dynamic sensorimotor integration. Broadly, these findings demonstrate that the brain leverages natural contingencies between behavior and expected sensory feedback to actively modulate perception.