PRISM ADAPTATION: EFFECTS OF TARGET-TYPE AND PERFORMANCE FEEDBACK
Ryan, Matthew P.
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When wearing prism goggles that displace vision laterally, the initial pointing errors are rapidly corrected. When the goggles are removed after a sufficient period of prism adaptation (PA), there is an aftereffect in spatial responding in the opposite direction of the original displacement. In this study 24 participants were tested using a computerized PA procedure to explore the effects of displacement direction (left/right), type of feedback during adaptation (hand/indirect), and type of target (fixed/non-fixed) on pointing error during 180 PA trials and the time-course of the aftereffect when measured in two ways: Subjective Straight Ahead (SSA) pointing (proprioceptive guidance towards perceived straight-ahead) and Visual Open Loop (VOL) pointing (visual and proprioceptive performance when pointing toward a straight-ahead target). During the initial stage of adaptation, all groups adjusted pointing in the opposite direction of prismatic displacement. Pointing error was similar for left and right goggle groups, but was more accurate and faster to stabilize with hand than indirect feedback. After pointing stabilized, the left-goggle/hand feedback group reached beyond targets (‘over-corrected’ pointing error), while other conditions failed to fully adjust pointing and remained ‘under-corrected’. In all groups, SSA aftereffects were weak or absent, while VOL aftereffects endured for at least 40-minutes. VOL aftereffects were larger following hand-feedback at all post-PA latencies, and for left-goggle groups at early post-PA latencies. Target-type affected performance during the stabilized-phase of adaptation, but did not influence SSA or VOL aftereffects. These results suggest that computerized PA had induced changes in vision but not proprioception, and provide novel evidence that the technology induced reliable aftereffects following both hand and indirect feedback PA. The results, when considered together with the study’s strengths and weaknesses, provide insight into how future studies might assess computerized-PA can be used to explore more complex attention and space representation process in healthy-normal and patients suffering from unilateral neglect.