Concurrent adaptations of left and right arms to opposite visual distortions

Abstract

Previous research has shown that subjects can adapt with either arm to an opposite visual distortion, and the two adaptive states can then be used in sequence to control the respective arm. To extend this finding, we exposed the left and right arms of our subjects to opposite-directed rotations of the visual field alternately for 20 s each, and determined the time-course of adaptation, as well as aftereffects without visual feedback under uni- and bimanual conditions. Our data confirm that two adaptive states can co-exist in the sensorimotor system, one for each arm. We further found that the time-course of adaptive improvement was similar for both arms, that the improvement was present as early as the first movement after a change of arm and discordance, and that the magnitude of adaptation was similar to control data yielded by a single arm and discordance. Taken together, these findings suggest that the two adaptive states were formed concurrently, and without mutual interference. We also observed significant aftereffects. They were smaller but still appreciable under bimanual conditions; the two arms moved at the same time in different directions even though they were aimed at a common visual target. This outcome indicates that the two adaptive states were not merely of a strategic nature, but rather changed the rules by which sensory information was transformed into motor outputs; it also suggests that the two states not only co-exist, but can also be engaged concurrently in movement control. The reduced aftereffects observed under bimanual conditions can be attributed to the well-known phenomenon of bimanual coupling, which is unrelated to adaptation.

Effect of Age on Learning to Drive a Virtual Coal Mine Shuttle Car

“…Error rate decreased during stage 2, however, during the final block more errors were still being made by the hand which had previously performed incompatible trials. This change in error rate performance is similar to that commonly found in adaptation studies, where an initial poorer performance is found when the condition changes from the adapted non-normal, or incompatible mapping, to an opposite or normal (compatible) mapping [20,23,28,29,33]. However, this performance decrement was not apparent in reaction time performance during stage 2 and reaction time reduced when the controlresponse relationship became consistently compatible, particularly for the hand which had previously carried out incompatible trials, resulting in no negative aftereffects for response rate.…”

“…Negative error rate after-effects are commonly found in adaptation studies when incompatible mappings relationships are changed to compatible [23,24]. This effect is generally short lived, as can be seen in error rate performance.…”

“…Adaptation researchers [23,24,34], on the other hand, suggest that practice results in high levels of performance improvement in tasks where the normal mapping has been distorted. Cunningham and Welch, 1994 [5], however, found that after six practice sessions in a visual-motor tracking task where short temporal periods of normal (compatible) mapping alternated with rotated (incompatible) mapping, performance in incompatible trials did not reach that for compatible trials.…”

“…Participants were not able to easily switch from the learned incompatible mapping to what would have been considered an 'automatic' compatible mapping. This aftereffect is often found in adaptation research, were performance decrements result when the task changes from an incompatible to normal or compatible mapping for both younger adults [23,24] and older adults [20].…”

The extent of interlimb transfer following adaptation to a novel visuomotor condition does not depend on awareness of the condition

“…They further proposed that the two arm controllers have independent (short term) memory resources that can be accessed by their counterpart, based on a finding that adapting to two opposing visuomotor rotations simultaneously by the two arms neither facilitates nor interferes with interlimb transfer (Wang and Sainburg 2003). This idea has been confirmed by other studies, which demonstrated that adaptations to two opposing rotations can coexist in the sensorimotor system, one for each arm (Bock et al 2005;Galea and Miall 2006).…”