Abstract

Under spatial misalignment of eye and hand induced by laterally displacing prisms subjects pointed 60 times at a visually implicit target or a visually explicit target. For different groups in each experiment, the hand became visible early in the sagittal pointing movement or only the fingertip was visible at the end of the movement. Adaptation to the optical misalignment during exposure was rapid, especially with early feedback; complete compensation for the misalignment was achieved within about 30 trials, and overcompensation occurred in later trials, specially with an explicit target. Adaptation measured with the misalignment removed and without visual feedback after blocks of 10 pointing trials was slow to develop, especially with delayed feedback and an implicit target; at most, about 40 compensation for the misalignment occurred after 60 trials. This difference between direct effects and aftereffects is discussed in terms of separable adaptive mechanisms that are activated by different error signals. Adaptive coordination is activated by error feedback and involves centrally located, strategically flexible, short-latency process to correct for sudden changes in operational precision that normally occur with short-term changes in coordination tasks. Adaptive alignment is activated automatically by spatially discordance between misalignment systems and involves distributed, long-latency processes to correct for slowly developing shifts in alignment among perceptual-motor components that normally occur with long-term drift. V.-R.