Walking impacts vision: Spatial and temporal frequency dependent changes to vision during locomotion

Contrast detection and direction discrimination of motion stimuli has been studied extensively using seated, head-fixed experiments. However, there is increasing evidence from research in non-human animals that activity, including locomotion, might alter processing of visual information. Locomotion dependent changes to visual perception in humans are currently not well understood, and findings have been mixed (Benjamin et al., 2018; Cao & Händel, 2018). To further investigate potential effects of locomotion, we employed a within-subject design, obtaining contrast detection thresholds from 14 participants. Participants completed a two-alternative forced-choice motion direction discrimination task while walking and sitting. Participants walked for 10-minute intervals on a treadmill at a self-selected speed (0.97-1.3 metres per second ). The stimulus was a vertical drifting Gabor presented in central vision (σ=0.375 degrees ). Four spatial frequencies (0.5, 2, 8 and 16 cycles per degree ) and two temporal frequencies (2 and 10 Hz) were tested in combination. A linear mixed model was used to analyse results. We found small but significant spatial and temporal frequency dependent differences in contrast sensitivity between the walking and sitting conditions. While contrast sensitivity for motion direction discrimination was similar for walking and sitting at 2 Hz, a significant difference in sensitivity was found between the conditions at 10 Hz, an effect that was principally driven by differences in the 2 cycles per degree condition. Results suggest there are spatial and temporal frequency dependent changes to contrast sensitivity during locomotion. We provide evidence that similar changes to those observed in non-human animals may exist in humans, and discuss what may be driving these changes.