Optic-flow and egocentric-direction strategies in walking: Central vs peripheral visual field

Abstract

The impact of a central or peripheral visual field loss on the vision strategy used to guide walking was determined by measuring walking paths of visually impaired participants. An immersive virtual environment was used to dissociate the expected paths of the optic-flow and egocentric-direction strategies by offsetting the walker's point of view from the actual direction of walking. Environments consisted of a goal within a forest, the goal alone, or the forest alone following a brief presentation of the goal. The first two environments allowed an evaluation of the visual information used in a goal-directed task whereas the third environment investigated the information used in a memory-guided task. Participants had either a central (CFL) or peripheral visual field loss (PFL) or were fully sighted (FS). Results showed that, for the goal-directed task, the CFL group was less influenced by optic flow than was an age-matched FS group. Optic flow decreased heading error by only 1.3 degrees (16%) in the CFL group compared to 3.6 degrees (42%) in the FS group. The PFL group showed an optic-flow influence (2.4 degrees or 26%) comparable to an older, age-matched FS group (2.9 degrees or 31%). For the memory-guided task, all but the PFL group had heading errors comparable to those obtained in the goal-alone scene, demonstrating the ability to use an egocentric-direction strategy with a stored representation of either the goal's position or an offset relative to a landmark instead of a visible goal. The paths of the PFL group veered significantly from the predicted paths of both the optic-flow and egocentric-direction strategies. The findings of this study suggest that central vision is important for using optic flow to guide walking, whereas peripheral vision is important for establishing and/or updating an accurate representation of spatial structure for navigation.

Kinematic Evaluation of Virtual Walking Trajectories

“…Visually guided locomotion has received considerable attention in the past [10,27,40,22,39,6], and two main strategies to move towards a goal have been identified. The first one, proposed by Gibson [10], leverages the optical flow created by the apparent motion of each point composing the sequence of images perceived by the walker during his motion [17].…”

“…The second strategy, proposed by Rushton [33], aims at aligning the locomotor axis with the perceived egocentric direction of the target to reach. Studies have shown that both strategies are used during locomotion steering [40], with a different predominance depending on the amount of available visual information [12,42,39].…”

Simulated Visual Field Loss Does Not Alter Turning Coordination in Healthy Young Adults

“…Left side picture is a frontal view of the goggles, while the right side picture is the participant's viewpoint through the goggles. of optic flow strategies, while the peripheral visual field is associated with egocentric direction strategies (Turano et al, 2005;Warren & Kurtz, 1992). In addition, common eye disorders among older adults involve impairments in one of these visual fields (Centers for Disease Control and Prevention, 2011).…”

“…Central and peripheral vision work synergistically to form the visual spectrum. Each visual field contributes different types of information for motion perception and locomotor control (Shapiro, Lu, Huang, Knight, & Ennis, 2010;Turano, Yu, Hao, & Hicks, 2005;Warren & Kurtz, 1992). The central visual field provides focal information advantageous for image contrast and displacement information but is limited to a small spatial area.…”

“…The central visual field provides focal information advantageous for image contrast and displacement information but is limited to a small spatial area. In contrast, the peripheral visual field provides information derived from a large spatial area but with less resolution and is advantageous for orientation and detecting the position of objects in the environment (Shapiro et al, 2010;Turano et al, 2005). As such, the central visual field has been associated with use of optic flow cues while the peripheral field has been associated with use of egocentric direction cues (Turano et al, 2005;Warren & Kurtz, 1992).…”