Bihaptic Localization Measures "Vision-for-Perception" More Reliably than "Vision-for-Action"

Abstract

Abstract: : Purpose: We previously reported that base-out prism glasses reduced kinesthetic matching (placing the unseen index finger under a target) estimates of perceived distance by 23% but did not affect bihaptic localization estimates (pointing both unseen forearms at a target) (0.2% reduction). In this study we tested the hypothesis that the differential response to prism glasses was related to slower execution speed for bihaptic localization than kinesthetic matching. Methods: Bihaptic and kinesthetic distance estimates were made by eight normally binocular subjects, with and without prism glasses. Informed consent was obtained prior to experimentation. In the previous protocol subjects were allowed 5 seconds of time to make distance estimates for targets at each of six randomized distances (20, 25, 30, 35, 40, & 45cm). In this study targets were presented at the same distances, but subjects were required to complete their distance estimates in less than 1.5 seconds. The order of all conditions was block randomized. Results: Responses were quantified by the slope of estimated distance on target distance. Prism significantly reduced slope for both estimators (f=52.3, p<.0001): by 13.4% for bihaptic localization (t=2.4, p<.02) and by 17.6% for kinesthetic matching (t=6.1, p<.0001). This fast response protocol did not affect kinesthetic slope variance but bihaptic slope variance increased by 75%. Conclusions: Base-out prism can influence bihaptic localization if responses are made quickly, but the increase of error under the fast response protocol might compromise its utility as a perceived distance estimator. Bihaptic localization more closely approximates verbal estimates of distance when slower and more reliable methods are used*. The speed effect suggests that the influence of prism on the bihaptic task is short-lived, and therefore that the influence of sensed accommodation & vergence (i.e., corollary discharge) on distance perception is brief. The brief duration of the sensed accommodation & vergence signal suggests that the signal is used primarily in "vision-for-action" rather than "vision-for-perception". * Love & McCormack, ARVO '03

Keywords: vision and action • depth • space perception