Meeting Abstract

101.10  Thursday, Jan. 7  The role of binocular vision in mammalian locomotion MITCHELL, Terence RT; Johns Hopkins University tmitche9@jhu.edu

Most vertebrates possess some overlap of the right and left visual fields. The region of overlap, the binocular field, contains visual cues that provide an accurate estimate of distance and three-dimensional shape. Primates have large binocular fields and theories of primate origins incorporate convergent eyes as part of the crown primate adaptational suite. Adaptational hypotheses must provide a functional role for a given trait if we are to believe evolution had a role in shaping any form – function complex. To date there is no experimental evidence demonstrating a role for binocular vision in ecologically relevant animal behavior. I predict that binocular vision is useful for guiding locomotion on complex substrates. I tested this by analyzing kinematic data of three Lemur catta, Felis catus, and Rattus norvegicus walking on continuous and discontinuous substrates under binocular and monocular conditions. All three species were effected by a loss of binocular cues. Lemurs exhibited the greatest change with a decrease in speed, increase in limb excursion, increase in crouching, and dramatic changes to wrist trajectory under monocular conditions. Guidance of locomotion on complex substrates provides one explanation as to why most vertebrates have some visual field overlap, and why all extant primates have large binocular fields. Primates have developed a host of adaptations related to locomotion in arboreal environments at large body size relative to substrate diameter. Long mobile forelimbs are used to bridge gaps and distribute weight in a complex discontinuous environment, and require a sensory system that can estimate distance and three-dimensional shape for the next few hand placements. Future theories of primate origins need to incorporate the growing body of evidence on primate locomotor adaptations.