Valentina Grigorova

The effect of rest breaks on human sensorimotor adaptation

We have studied the effect of rest breaks on sensorimotor adaptation to rotated visual feedback in a pointing task. Adaptive improvement was significantly poorer after 1-s breaks than after 5–40-s breaks, with no significant difference among the latter break durations. The benefit of >1-s breaks emerged soon after the onset of adaptation, and then remained steady throughout the adaptation, retention (next day), and persistence (no feedback) phases. This pattern of findings indicates that break-induced facilitation is not a result of strategic adjustments, motivation, or recovery from fatigue, but rather to consolidation of previously acquired sensorimotor recalibration rules.

Adaptation of eye and hand movements to target displacements of different size

Previous work has documented that the direction of eye and hand movements can be adaptively modified using the double-step paradigm. Here we report that both motor systems adapt not only to small direction steps (5° gaze angle) but also to large ones (28° gaze angle). However, the magnitude of adaptation did not increase with step size, and the relative magnitude of adaptation therefore decreased from 67% with small steps to 15% with large steps. This decreasing efficiency of adaptation may reflect the participation of directionally selective neural circuits in double-step adaptation.

Directional adaptation of reactive saccades and hand pointing movements is not independent.

ABSTRACT It is a matter of debate whether reactive saccades and hand pointing movements share common adaptive mechanism. To find out, the authors used a double-step paradigm in which the direction either of eye or of hand movements was adaptively modified in a first block of 300 trials, and the direction of the other motor system was then modified with opposite polarity in a second block of 300 trials. In a third block, single-step stimuli were used to test for after effects. The authors found that subjects adapted in the second block less well than in the first, and that aftereffects were adequate for the first rather than the second block. When the second block was extended to 500 trials, adaptation was still poor but aftereffects were now adequate for the second block. From this the authors concluded that double-step adaptation of the first motor system interferes with the subsequent adaptation of the other motor system (i.e., the adaptive mechanisms for eyes and hand are not independent).

On the distribution of attention in a visuo-manual adaptation task

We have observed in a previous study that adaptation to reversed visual feedback in a tracking task is better when subjects are instructed to look at the cursor providing feedback (group C) rather than at the target (group T). Since both groups actually looked at the target, irrespective of their instructions, we suggested that the advantage of group C is not related to their eye movements, but rather to their allocation of spatial attention. The present study scrutinized this view by combining the same adaptation task with a concurrent reaction-time task, designed to spread subjects’ attention across the whole display area. Again, subjects were instructed to look at the cursor or at the target, and again, both groups actually looked at the target. Adaptation was similar to group T, and poorer than group C of the previous study. We therefore concluded that adaptation indeed depends on the subjects’ allocation of attention: focussing attention mainly on the target, or spreading it across the whole display area, is not as good as distributing attention between target and cursor.

The role of eye movements in visuo-manual adaptation

The present study evaluated the role of eye movements for manual adaptation to reversed vision. Subjects tracked a visual target using a mouse-driven cursor. In Experiment A, they were instructed to look at the target, look at the cursor, fixate straight ahead, or received no instructions regarding eye movements (Groups T, C, F, and N, respectively). Experiment B involved Groups T and C only. In accordance with literature, baseline manual tracking was more accurate when subjects were instructed to move their eyes rather than to fixate straight ahead. In contrast, no such benefit was observed for the adaptive improvement of tracking. We therefore concluded that transfer of information from the oculomotor to the hand motor system enhances the ongoing control of hand movements but not their adaptive modification; probably because the large computational demand of adaptation does not allow an additional processing of supplementary oculomotor signals. We further found adaptation to be worse in T than in any other group. In particular, adaptation was worse in T than in C although eye movements were the same: subjects in both groups moved their eyes in close relationship with the target rather than the cursor, Group C thus disobeying our instructions. The deficient performance of Group T is therefore not related to eye movements per se, but rather to our instructions. We conclude that an independently moving target strongly attracts eye movements independent of instruction (i.e. Groups T and C), but instructions may redirect spatially selective attention (i.e. Group T vs C), and thus influence adaptation.

Concurrent adaptation of reactive saccades and hand pointing movements to equal and to opposite changes of target direction

Eye as well as hand movements can adapt to double-step target displacements, but it is still controversial whether both motor systems use common or distinct adaptive mechanisms. Here, we posit that analyses of the concurrent adaptation of both motor systems to equal versus different double-steps may provide more conclusive evidence than previous work about the transfer of adaptation from one motor system to the other. Forty subjects adapted to double-steps which called for a change of response direction. The same (group S) or the opposite change (group O) was required for eyes and hand. Group ON equaled O, except that no visual feedback of the hand was provided. Groups E and H served as controls for eyes-only and hand-only adaptation, respectively. We found no differences between groups or motor systems when comparing S, E and H. Adaptation was faster in O than in S, E and H, and faster still in ON. However, the magnitude of eye adaptation was much smaller in O and ON than in S, E and H. We conclude that concurrent adaptation of eye and hand directions to opposite double-steps attenuates recalibration which, at least for the hand, is largely replaced by workaround strategies. The mechanisms for eye and hand adaptation therefore seem to be coupled, in a way that hinders divergent recalibration of both motor systems. The possible neuronal substrate for our findings is discussed.

Effects of old age and resource demand on double-step adaptation of saccadic eye movements

Abstract It is still unknown whether adaptation of saccades—like that of arm movements—deteriorates in the presence of a concurrent resource-demanding task, and whether it is affected by old age. We therefore compared double-step adaptation of saccade directions in young and older persons exposed to the adaptation task only (groups CY & CO), to the adaptation task and a spatially adjacent manual tracking task (AY & AO) or to the adaptation task and a spatially distant manual tracking task (DY & DO). Adaptation was similar in all groups except DO: the latter group showed no consistent adaptation and no adequate aftereffects. Tracking improved little by practice in all groups except AY, where the improvement was substantial. Our data therefore provide no evidence for an impact of old age and resource demand on saccadic adaptation, possibly because the neural substrate partly differs from that for arm adaptation. The lack of adaptation in DO probably reflects the well-known shrinkage of the functional field of view in old age.

Adaptation of hand movements to double-step targets and to distorted visual feedback: Evidence for shared mechanisms

Visuomotor adaptation of hand movements has been studied with two paradigms: double-step targets and distorted visual feedback. Here we investigate whether both procedures are based on a common adaptive mechanism. Subjects adapted either to double-step targets or to distorted feedback, each requiring a change of response angle by -15°. The magnitude of adaptation was larger with rotated feedback but magnitude of aftereffects was comparable, suggesting that the difference was due to strategic effects rather than visuomotor recalibration. Most importantly, subjects who adapted to double-step targets and were then exposed to rotated feedback performed as well as subjects who had fully adapted to rotated feedback, i.e., there was nearly 100% transfer from double-steps to rotations; likewise, the transfer from rotations to double-steps was almost 100%. From this we conclude that both types of adaptation share a common mechanism for recalibration.

Adaptation of Reactive Saccades is Influenced by Unconscious Priming of the Attention Focus.

ABSTRACT The authors investigated whether the size of the attention focus can influence saccadic adaptation, and whether this influence changes in older age. Using the scrambled sentence task, young and older participants were either primed for a wide attention focus, or primed of a narrow attention focus, or were not primed for any specific attention focus. Subsequently, all participants underwent a double-step saccadic adaptation paradigm aimed at changing the direction of reflexive saccades. The authors found that compared to the nonprimed control group, priming for a wide attention focus enhanced saccadic adaptation in both age groups by a similar amount; the benefit persisted throughout the adaptation phase, but was absent during the deadaptation phase. In contrast, the authors found no effects of priming with a narrow attention focus on saccadic adaptation. From this the authors conclude that a wide attention focus is beneficial for workaround strategies but not for adaptive recalibration, and that those benefits are similar in young and older persons.

Alternating Adaptation of Eye and Hand Movements to Opposite Directed Double Steps

ABSTRACT Eye and hand movements can adapt to a variety of sensorimotor discordances. Studies on adaptation of movement directions suggest that the oculomotor and the hand motor system access the same adaptive mechanism related to the polarity of a discordance, because concurrent adaptations to opposite directed discordances strongly interfere. The authors scrutinized whether participants adapt their hand and eye movements to opposite directions (clockwise/counterclockwise) when both motor systems are alternatingly exposed to opposite directed double steps, and whether such adaptation is influenced by the allocation of effector to adaptation direction. The results showed that hand and eye movements adapted to opposite directions, but adaptation was biased to the counterclockwise direction. Aftereffects emerged nearly unbiased and independently for both motor systems. The authors conclude that the oculomotor and the hand motor system use independent mechanisms when they adapt to opposite polarities, although they interact during adaptation or concurrent performance.