Retinal optic flow during natural locomotion

Abstract

We examine the structure of the visual motion projected on the retina during natural locomotion in real world environments. Bipedal gait generates a complex, rhythmic pattern of head translation and rotation in space, so without gaze stabilization mechanisms such as the vestibular-ocular-reflex (VOR) a walker’s visually specified heading would vary dramatically throughout the gait cycle. The act of fixation on stable points in the environment nulls image motion at the fovea, resulting in stable patterns of outflow on the retinae centered on the point of fixation. These outflowing patterns retain a higher order structure that is informative about the stabilized trajectory of the eye through space. We measure this structure by applying the curl and divergence operations on the retinal flow velocity vector fields and found features that may be valuable for the control of locomotion. In particular, the sign and magnitude of foveal curl in retinal flow specifies the body’s trajectory relative to the gaze point, while the point of maximum divergence in the retinal flow field specifies the walker’s instantaneous overground velocity/momentum vector in retinotopic coordinates. Assuming that walkers can determine the body position relative to gaze direction, these time-varying retinotopic cues for the body’s momentum could provide a visual control signal for locomotion over complex terrain. In contrast, the temporal variation of the eye-movement-free, head-centered flow fields is large enough to be problematic for use in steering towards a goal. Consideration of optic flow in the context of real-world locomotion therefore suggests a re-evaluation of the role of optic flow in the control of action during natural behavior.

Optic flow in the natural habitats of zebrafish supports spatial biases in visual self-motion estimation

“…Humans can use optic flow cues to predict collisions, 8 estimate direction and distance of travel, 9 , 10 maintain upright posture, 11 , 12 and walk toward targets. 13 – 15 In rodents, optic flow has been shown to affect representations of heading direction 16 and to be combined with proprioceptive information during locomotion. 17 …”

“…These results bring together converging lines of evidence that biases in motion estimation reflect a general strategy to optimally measure behaviorally relevant information from natural environments. 14 , 15 , 37 , 39 – 44 …”

Active vision during prey-capture in wild marmoset monkeys

“…This feature further underscores the advantages of prey-capture for understanding the factors affecting problem solving and cognitive control in primates under variable natural conditions. As not all theoretical models of vision developed in more traditional laboratory settings are likely reflective of how this system functions under real-world scenarios 31 , natural primate behaviors such as prey-capture will likely be necessary to elucidate remaining key questions about primate brain function.…”

Active vision during prey capture in wild marmoset monkeys

“…The behavioral variability that emerges due to an interaction between a presumably ideal strategy for obtaining prey and the specific ecological challenges underscores the advantages of primate prey capture to elucidate the likely supporting perceptual and cognitive processing, including decision-making and cognitive control, under natural variable conditions, and can be used as principles that guide future experimental work on these key issues. As not all theoretical models of vision developed in more traditional laboratory settings are likely reflective of how this system functions under real-world scenarios, 33 natural primate behaviors such as prey capture will likely be necessary to elucidate remaining key questions about primate brain function.…”