The Role of Visual and Proprioceptive Limb Information in Object Size and Affordance Judgments

In the mirror illusion, visual information from a mirror reflection of one hand influences the perceived location of the other hand. Holmes, Crozier, and Spence (2004) demonstrated this visual capture effect on a spatial localization task in which visual information was found to influence reaching movements towards a target when the seen (in the mirror) and felt (proprioception) position of the hand did not match. In this present experiment, the conflict between vision and proprioception was examined by means of a task in which participants adjusted the physical distance between their two hands to match targets of different lengths. In each trial, participants viewed their visible hand and its reflection in a mirror, while their unseen hand was positioned at one of four locations located behind the mirror. At all times, the visible hand was positioned fourteen cm in front of the mirror, and as such, the unseen hand always appeared to be twenty-eight cm from the visible hand regardless of its actual position. While viewing their visible hand and its reflection, participants performed simultaneous finger movements with both hands to maximize the illusion. Participants then viewed a target block and repositioned their unseen hand such that the distance between their hands matched the block length. Results suggest that movement of the unseen hand relative to the visible hand was biased by visual information from the mirror, and this bias increased as the visual-proprioceptive conflict increased. These results suggest that the visual information about hand position overrode the proprioceptive information when the hands were used to indicate perceived object length. Additional experiments will use affordance judgments to further investigate how visual and proprioceptive information affect judgments of limb location and action capabilities.https://ecommons.udayton.edu/stander_posters/1155/thumbnail.jp