Retinal optic flow during natural locomotion
Fig 6
Retinal optic flow during natural locomotion.
Retinal flow simulation based on integrated eye and full-body motion of an individual walking over real world terrain. Panels A-C are based on frames taken from S2 Video, which shows data derived from a subject walking in the Woodchips condition under the Ground Looking instructions (S10 Video). (A) shows a case where the fixation point (pink line) is aligned with ground projection of the eye’s velocity vector (green arrow). Middle circular panel shows simulated optic flow based on fixation location and body movement. Left and right upper circular panels show the results of applying the curl and divergence operators to the retinal flow field in the middle panel. Left and right bottom panels show the projection of the curl (left) and divergence (right) onto a flat ground plane. The green arrow shows the walker’s instantaneous velocity vector (scaled for visibility), which always passes through the maximum of the retinal divergence field(which always lies within the foveal isoline (blue circle)) (see Fig 7). (B) and (C) show cases where the fixation point is to the left or right of the eye’s velocity vector (respectively). Fixation to the left of the eye’s velocity vector (B) results in a global counter-clockwise rotation of the retinal flow field and positive retinal curl at the fovea, while fixation to the right of the eye’s velocity vector results in clockwise flow and negative curl at the fovea (Fig 7).