Figure 2.

Changes in optic flow speed perception during locomotion. (a) While walking, subjects perceive faster optic flow speeds to match optic flow speeds viewed when stationary, indicating that optic flow appears slower. This is illustrated by the point of subjective equality (indicated by dashed lines) being shifted to a faster visual speed compared to a reference speed (indicated by black triangle) viewed when stationary (illustration of results from [11]). (b) During walking subjects exhibit increased sensitivity to optic flow speeds faster than a threshold speed that approximately matches average walking speed (approx. 125 cm s⁻¹ in [11]). As a result, psychometric curves for optic flow speed discrimination are slightly steeper when subjects are walking, indicating improved discrimination of optic flow speeds (illustration of results from [11]).