Recently, Ayaz et al. (2013) reported a remarkable finding: surround suppression, as measured by V1 activation in mice, is substantially reduced during locomotion (running in place). Does low-level visual processing change in humans when they are walking? Such a change would recast our understanding of the relationship between vision and action and might explain previously observed effects of walking on motion perception (e.g., Durgin, 2009). To assess how the findings of Ayaz et al. extend to behavioural effects in human vision, we tested participants during locomotion and used an established behavioural measure of perceptual suppression based on Tadin et al. (2003). Tadin et al. demonstrated that duration thresholds for detecting the motion direction of a high-contrast grating increase with stimulus size. Our participants completed a simple motion-discrimination task in two conditions (modelled after Ayaz et al.): (1) standing in a stationary position and (2) walking on a treadmill. We replicated the expected behavioural effects in the baseline (standing) condition (i.e., increased difficulty discriminating the direction of motion for larger stimuli); however, we also found identical performance in the walking condition. Our results may indicate that changes in early visual areas are not predictive of behavioural suppression effects, or they may reflect a fundamental difference between the structures of visual systems. In either case, as discrimination thresholds were indistinguishable between the standing and walking conditions, we do not find support for an interaction between locomotion and spatial suppression in humans.