ADAPTIVE-CHANGES IN SACCADE AMPLITUDE - OCULOCENTRIC OR ORBITOCENTRICMAPPING

saccadic system rapidly adjusts the amplitude of refixation movements to visual targets when abnormal postsaccadic errors occur, This is cal led rapid saccadic adaptation. It is not yet clear whether this form o f adaptation produces changes related to oculocentric mechanisms, such as retinal error or motor error, or orbitocentric mechanisms, such as eye or gaze position. These experiments were designed to test whether rapid saccadic adaptation was orbitocentric, oculocentric, or both by creating a precise sensory motor mismatch between the visual target a nd the required saccade, Measurements were made to determine adaptive changes as a function of (1) saccade direction; (2) eye position; and (3) saccade amplitude, Changes were found to be amplitude- and directi on-specific but changes were generalized across a broad range of orbit al positions. Two conditions of adaptation: increasing and decreasing amplitude, produced quantitatively similar results, indicating that si milar mechanisms underlie both processes. Thus, these data support the view that changes during rapid saccadic adaptation are organized prin cipally in a retina-referenced (oculocentric) map, but only broadly, i f at all, in a head-referenced (orbitocentric) map. The changes are co nsistent with a mechanism represented in a spatial mapping of either r etinal or motor error. Copyright (C) 1996 Elsevier Science Ltd.