Prism exposure aftereffects and direct effects for different movement and feedback times

The effects of movement time and time to visual feedback (feedback time) on prism exposure aftereffects and direct effects were studied. In Experiment 1, the participants' (N = 60) pointing limb became visible early in the mo vement (.2-s feedback time), and eye-head aftereffects increased with incre asing movement time (.5 to 3.0 s), but larger hand-head aftereffects showed little change. Direct effects (terminal error during exposure) showed near -perfect compensation for the prismatic displacement (11.4 diopters) when m ovement time was short but decreasing compensation with longer movement tim es. In Experiment 2, participants' (N = 48) eye-head aftereffects increased and their larger hand-head aftereffects decreased with increasing movement time (2.0 and 3.0 s), especially when feedback time increased (.25 and 1.5 s). Direct effects showed increasing overcompensation for longer movement and feedback times. Those results suggest that aftereffects and direct effe cts measure distinct adaptive processes, namely, spatial realignment,and st rategic control, respectively. Differences in movement and feedback times e voke different eye-hand coordination strategies and consequent direct effec ts. Realignment aftereffects also depend upon the coordination strategy dep loyed, but not all strategies support realignment. Moreover, realignment is transparent to strategic control and, when added to strategic correction, may produce nonadaptive performance.