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A. Pelah, A. E. I. Thurrell; Reduction of perceived visual speed during locomotion: Evidence for quadrupedal perceptual pathways in human?. Journal of Vision 2001;1(3):307. doi: https://doi.org/10.1167/1.3.307.
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PURPOSE: We reported previously that perceived optic flow speed is reduced linearly with walking speed (Thurrell et al. 1998 Perception 27 pp147–148), a mechanism we postulate would preserve world constancy during normal self-motion. We consider here whether the reduction occurs also during activities that are progressively less characteristic of upright locomotion. METHODS: Subjects viewed an optic flow reference stimulus for 15 s while applying at an instructed rate (i.e. very slow, slow,…,very fast) one of the following activities: a) walking; b) leg pedaling a stationary bicycle; c) arm pedalling a stationary bicycle; and d) bimanual 4 finger tapping. Subjects then ceased the motor activity and attempted to match the reference speed by adjusting optic flow with a hand-held knob. Notionally, human walking corresponds to stereotypical bipedal locomotion, while muscle activation patterns during cycling are rather different, and arm and finger activities are progressively different still. RESULTS: Confirming previous findings, subjects made speed settings that indicated a perceived underestimation of optic flow during walking. A weaker yet significant reduction also occurred during leg pedaling, and one weaker still occurred for arm pedaling. Index finger tapping had no effect on perceived optic flow speed. CONCLUSIONS: The presence of a weaker effect for leg-pedaling than for walking (and the absence of one for finger tapping) suggests that the influence of motor activity on perception of optic flow may depend on the degree of similarity of the activity to everyday, upright locomotion. The presence of a reduction during arm pedaling may be interpreted as the influence of vestigial or infantile quadrupedal pathways in humans.
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