Here we examine the ways that the optic flow patterns experienced during natural locomotion are shaped by the movement of the observer through their environments. By recording body motion during locomotion in natural terrain, we demonstrate that head-centered optic flow is highly unstable regardless of whether the walker’s head (and eye) is directed towards a distant target or at the ground nearby to monitor foothold selection. In contrast, VOR-mediated retinal optic flow has stable, reliable features that may be valuable for the control of locomotion. In particular, we found that a walker can determine whether they will pass to the left or right of their fixation point by observing the sign and magnitude of the curl of the flow field at the fovea. In addition, the divergence map of the retinal flow field provides a cue for the walker’s overground velocity/momentum vector in retinotopic coordinates, which may be an essential part of the visual identification of footholds during locomotion over complex terrain. These findings casts doubt on the assumption that accurate perception of heading direction requires correction for the effects of eccentric gaze, as has long been assumed. The present analysis of retinal flow patterns during the gait cycle suggests an alternative interpretation of the way flow is used for both perception of heading and the control of locomotion in the natural world.
bioRxiv Subject Collection: Neuroscience