Effects of scaling shoulder width in VR on reachability and pass-through-ability affordances

Perceiving affordances, the action-possibilities of a system in an environment, is a survival key for the system (Gibson, 1966). Changing invariants for the system shapes its affordance perception (Warren & Whang, 1987). Pass-through-ability of an aperture, as a perceived affordance, is determined by the fit between the apparent aspects of the environment (e.g., perceived gap) and the perceived body scale. Changing body perception in real life depends on using tools such as a wheelchair or a long stick (Higuchi, Cinelli, Greig, & Patla, 2006; Higuchi, Cinelli, & Patla, 2009). Here, in order to understand the effects of body scaling on the affordance of pass-through-ability and reachability, we conducted a virtual reality and a simulation study. Participants were assigned to different virtual shoulder widths scaled to their real size (narrow, normal and wide). In the experiment, they were asked to walk naturally to pass through an aperture without colliding and reach a target on a table. The success rate of passing through an aperture and the speed were similar in all conditions, which implied that participants adapted their virtual bodies. We also showed that participants were closer to the target when assigned narrow compared to a normal-size shoulder, suggesting that participants thought their body became smaller, so they moved closer to the target. In order to control the adaptation for conditions, we also conducted a perceptual judgement experiment. Also reflected in the perceptual judgements, participants with narrow virtual shoulders thought that they had smaller shoulder width, an effect not observed in the wide shoulder condition, which together demonstrate an asymmetry in the effects of body scaling.