Understanding the contribution of binocular vision to the control of adaptive locomotion

Abstract

Abstract. Although the contribution of binocular vision to reach-to-grasp movements has been extensively studied, it has been largely ignored in locomotion. The aim of these studies was to explore the role of binocular vision during the approach phase and step over the obstacle and the contribution of head movements to acquisition of depth information under monocular vision. Binocular and monocular vision was manipulated in different phases using either an eye patch or liquid crystal glasses. Head movement relative to the trunk was restricted in the first experiment by a modified Ferno Universal Head Immobilizer attached to a rigid board strapped to the participant's back. Whole body kinematics were collected by placing infrared diodes on anatomical landmarks and using an Optotrak imaging system. Several measures related to head and limb movement were analyzed. Three major findings emerged from these studies. First, binocular vision is important for the acquisition of accurate information about the surrounding environment: accuracy but not precision of limb elevation over the obstacle was adversely affected when binocular vision was unavailable. Second, motion parallax due to self-motion provides the most critical depth information and it can be used to partially compensate for the loss of binocular vision. Although head movement is not essential to augment depth information, it is important for reorientation of the visual field to obtain the necessary information about the moving limbs when visual field is suddenly limited under monocular vision. Third, step over the obstacle is pre-planned based on visual information acquired during the approach phase: changes in visual condition during the adaptive step do not influence the limb trajectory. Collectively these three studies provide unique insights into the contribution of binocular vision during adaptive locomotion.

Visual control of action in step descent

“…This kind of 'contraction bias' strategy has also been reported in open-loop reaching movements (Tresilian et al, 1999). (Patla et al, 2002, Chajka et al, 2007. In these studies it may also be the case that monocular viewing caused participants to add a safety margin onto their estimates because of a reduced field of view.…”

“…It has been claimed that this provides a cue to depth in locomotor tasks. For example participants increase toe clearance over an obstacle when stepping over it with monocular viewing (Patla, Niechwiej, Racco & Goodale, 2002). Likewise in an obstacle avoidance task (Chajka, Vecellio, Hayhoe & Gillam, 2007) monocular viewing causes participants to make longer fixations on obstacles and the floor, and to increase total movement time.…”

Obstacle crossing in lower limb amputees

“…Leading with the prosthetic limb has advantages. During crossing with the leading limb the movement can be controlled by visual feedback, while trailing limb trajectory cannot be guided by vision [4,14,24,27,28]. Moreover, at toe-off prior to obstacle crossing the foot of the leading limb is one step length further away from the obstacle than the foot of the trailing limb.…”

Visuo-locomotor coordination for direction changes in a manual wheelchair as compared to biped locomotion in healthy subjects

“…Since the subjects were novice in MWC navigation, this behavior may have been a safer way to navigate, reducing the risk of a potential collision. It has been demonstrated that people tend to maintain a greater safety margin for locomotion in novel situations [15]. While it has been shown that able-bodied persons inexperienced with WC locomotion adapt over minutes and maintain learned skills over weeks [16], they are certainly not experts in MWC locomotion.…”