Perceived visual speed while walking: Adding to subtraction

Perceived visual speed has been reported to be reduced during walking compared to standing still. This effect has been attributed to an automatic subtraction of part of the walking speed from the visual speed (Durgin et al, 2005 Journal of Experimental Psychology: Human Perception and Performance 31 339 ^ 353). Here, we show that both the magnitude and the direction of this `reduction‘ depend on visual speed. Observers compared visual speed of a simulated ground plane (presented through an HMD) while standing and walking (1.1 m sÿ1). PSEs, estimated for three standard speeds during walking (1.0, 2.0, 3.0 m sÿ1 simulated speed), increased approximately linearly with the standard speed, with a slope 4 1. For the lowest standard speed, the PSEs were lower than the standard speed, whereas they were higher for the highest standard speed. The latter is clearly incompatible with an automatic subtraction effect. The results suggest that, contrary to what Durgin et al (2005) claim, the effect of walking on perceived visual speed is not independent of the visual speed and raise questions regarding the functional role of the subtraction effect