Abstract
Tasks such as walking, reaching, and standing require differing levels of postural stability. Postural equilibrium is necessary to perceive the location of objects (Lee, Pacheco, & Newell, 2018). This study compared affordance (Gibson, 1979) judgements of reachability between tasks that place different constraints on maintaining balance. The method included a 3D virtual reality (VR) environment with a stimulus object placed at different distances from the observer. Using a within subjects design, participants were asked to make judgements on reachability while in a standard stance condition as well as two separate active balance conditions (yoga tree pose, and toe-to-heel pose). Feedback on accuracy was not provided, and participants were not allowed to attempt to reach. Response time, affordance judgments (reachable, not reachable), and head movements were recorded on each trial. Specifically, head movement time series were recorded by harnessing position data from the Oculus Rift VR goggles. Consistent with recent research on reaching ability (Weast & Proffitt, 2018), the reachability boundary occurred around 120% of arm length, indicating overestimation of action capability. Response times increased with distance, and were smallest for the most difficult yoga tree pose, suggesting that in order to maintain a difficult pose, responding had to be sped up. Head movement amplitude and total amount of movements increased with increases in balance demands. Surprisingly, the coefficient of variation was comparable in the two poses that had increased balance requirements, and was more extreme in a less constrained, ostensibly easier pose for the shortest and longest distances, indicating a pose by distance interaction. The insights gathered from this study will provide a fuller understanding of the perception of affordances in everyday tasks such as reaching and grasping.