2/4/2025 | 3:30 PM - 5:30 PM | Grand Peninsula D

Convexity biases in stereoscopically viewed ground terrain

Author(s)

Brittney Hartle | York University
Robert Allison | York University
Laurie Wilcox | York University

Abstract

Judging the ‘lay of the land’ during locomotion relies on the integration of an array of perceptual and motor cues. We demonstrated that stereopsis plays a substantial role in discriminating surface perturbations of ground terrain; however, observers were often biased towards perceiving convex surfaces when shading cues were highly salient. The aim of the current study was to 1) determine if this bias is replicated under different viewing conditions, and if so, 2) to better understand the source of the phenomenon. To this end we first replicated our previous study. We then show that the convexity bias was not driven by unreliable stereoscopic cues in low illumination, but instead depended on the presence of the shading itself. We did so by varying the availability of binocular disparity by (i) only showing half of the surface binocularly or (ii) presenting the full surface to one eye and half of the surface to the other. The convexity bias only overrides stereopsis when it defines a smooth coherent surface with intense shading. Importantly, our observers possessed normal stereoacuity, yet 50% of them used an ambiguous shading cue to judge terrain. Under impoverished viewing, this could lead to potentially dangerous errors during locomotion.