Date of Award

Spring 2019

Degree Type

Masters Thesis

Degree Name

Master of Arts (MA)



Committee Chair

Alen Hajnal

Committee Chair School


Committee Member 2

Bonnie Nicholson

Committee Member 2 School


Committee Member 3

Richard Mohn

Committee Member 3 School



Tasks such as standing and reaching require differing levels of postural stability. Postural equilibrium is necessary to perceive the location of objects (Lee, Pacheco, & Newell, 2018). Visual perception of whether an object is within reach was investigated while standing upright. Participants viewed a 3D virtual reality (VR) environment with a stimulus object (red ball) placed at different egocentric distances. Participants made affordance judgements 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. Consistent with recent research on reaching ability (Weast & Proffitt, 2018), the perceived action boundary occurred around 120% of arm length, indicating overestimation of perceived reaching ability. Response times increased with distance, and were shortest for the most difficult yoga tree pose. Head movement amplitude 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. More complex descriptors of postural sway (i.e. multifractality) were predictive of perception while in the tree pose and the toe-to-heel pose, as compared to control stance. This demonstrates that standard measures of central tendency are not sufficient for describing multiscale interactions of postural dynamics in functional tasks.