Differential effects of walking across visual cortical processing stages.

Perceptual processes are almost exclusively investigated and understood under marked movement restriction, while natural behaviour includes pronounced movements. Recent human studies have indicated a profound influence of body movement on early visual responses (e.g., evoked components around 100 msec in EEG, electroencephalogram). However, very little is known about the influence of free walking on later visual responses (e.g., responses related to visual selective attention in a later time window than the stimulus evoked N1 component). In the current study, we measured neural signals (EEG) and behavioural performance in a visual selective attention task while participants were standing or freely walking. The results showed that walking was associated with an amplification of early sensory-evoked potential as indicated by the N1 component. Interestingly, neural indexes of the succeeding processing stages of stimulus discrimination and identification, namely the N2pc component and alpha oscillations, and the eventual behavioural measures were comparable between standing and walking. Additionally, in both standing and walking conditions, an overall advantage in target processing for the right visual field was observed. Our work provides evidence that the early sensory processing is enhanced during locomotion while the succeeding processing steps in a later time window are not modulated by locomotion. We conclude that walking has differential effects across visual cortical processing stages.