Changes in Auditory Localization following Prismatic Exposure under Continuous and Terminal Visual Feedback

Abstract

Intermanual transfer of prism aftereffects may be due to an altered interpretation of eye position (Kalil & Freedman, 19GG), an altered interpretation of head position (Harris, 1965), or other factors. This study attempts to evaluate the first two alternatives by requiring blindfolded Ss to point to auditory targets both before and after prism-wearing sessions. If such transfer is due to an altered interpretation of eye position, it should not result when tested with unseen auditory targets; if intermanual transfer is due to an altered interpretation of head position, the intra-aural time and intensity differences of an auditory target should imply that the target is at a given direction from the sensed position of the head, and transfer should result. Sixteen right-handed male Ss wore binocular prisms in four exposure sessions derived by systematically combining (1) prism-base orientation-30 diopters base right vs 30 diopters base left, and (2) visual feedback condition--continuous feedback vs terminal feedback (see Cohen, 1967, 1973). Each session lasted 5 min., and every 5 sec., S reached with his right hand for a target peg embedded in a lucite platform approximately 45 cm. from his eyes. Both before and after each exposure session, S was blindfolded and pointed with each hand to an auditory target located 25 to the right, at, or 25 to the left of his midline. Three responses, recorded photographically, were made with each hand for each target position. Changes in localization from pre-exposure to postexposure were computed across all targets for each hand in each session, and the changes obtained with prismbase left and prism-base right exposures were combined to provide a measure of mean adaptive shift in degrees rotation about S's midline. Following exposure under continuous visual feedback, aftereffects were restricted to the exposure arm, i.e., the arm that was viewed through the prisms during the exposure session (Exposed arm mean shift = 2.73, t = 6.66, p < ,001; Unexposed arm mean shift = 0.25, 8 = .35, ns). Following exposure under terminal visual feedback, aftereffects were obtained from both arms (Exposed arm mean shift = 3.2g0, t = 6.09, p < .001; Unexposed arm mean shift = 2.0Y0, t = 2.45, p < ,025). Intermanual transfer of prism aftereffects was obtained with unseen auditory targets, but only following exposure with terminal visual feedback. The results suggest that such transfer is not due to a change in the sensed position of the eyes in their sockets, but to change in the sensed posirion of the head relative to the trunk, since the position of the head, and not of the eyes, serves as the basis for processing informarion underlying auditory localization.