Mathias Hegele

Adaptation to visuomotor rotations in younger and older adults.

Adaptation to a visuomotor rotation is known to be impaired at older adult age. The authors examined whether the impairment is present already at preretirement age and whether it depends on the difficulty of the adaptation task. Moreover, the authors tested predictions of the hypothesis that the age-related impairment pertains primarily to strategic corrections and the explicit knowledge on which they are based but not to the acquisition of an (implicit) internal model of the novel visuomotor transformation. The authors found an age-related impairment of adaptation and explicit knowledge already at preretirement age but no age-related change of aftereffects. With an incremental simplification of the adaptation task, age-related changes were able to be eliminated. Individual differences of the quality of explicit knowledge were associated with differences of adaptation, but not of aftereffects. When age groups were matched by explicit knowledge, age-related impairments of adaptation largely disappeared. However, a reliable difference remained in one of the experiments, suggesting that other processes of adjustment to a visuomotor rotation might be affected by aging as well.

Constraints on visuo-motor adaptation depend on the type of visual feedback during practice

Adaptation to a novel visuo-motor gain has been found to generalize across target directions, whereas simultaneous adaptation to different direction-related visuo-motor gains turned out to be impossible. We ask whether this is a rigid constraint on human adaptability or a soft constraint that can be overcome by optimized conditions of practice. In particular, we compared practice with continuous visual feedback, as used in previous studies, to practice with terminal visual feedback. With terminal visual feedback only the final positions of the movements are shown. Both kinds of visual feedback in principle can serve the acquisition of an internal model of direction-related visuo-motor gains, but with continuous feedback on-line visual closed-loop control permits accurate movements without access to an internal model. Whereas we found no indication of visuo-motor adaptation after continuous-feedback practice, there was adaptation after terminal-feedback practice. This was revealed both by (direction-related) adaptive shifts of movement amplitudes in an open-loop test with cued visuo-motor transformation and by (direction-related) aftereffects in an open-loop test with absence of the visuo-motor transformation being cued. None of the two groups gave evidence of explicit knowledge of the direction-related visuo-motor gains. These findings show that constraints on human adaptability can depend on the kind of experience with visuo-motor transformations, in particular on the kind of feedback during practice.

Implicit and explicit components of dual adaptation to visuomotor rotations.

Concurrent adaptation to two different visuomotor transformations has been shown to be possible as long as discriminative contextual cues are available. The authors examined explicit and implicit components of visually cued dual adaptation in younger and older adults. They found that only young adults, but not old adults, produced appropriate adaptive shifts of hand-movement direction to compensate for the visuomotor rotations. Aftereffects, conceived as a measure of implicit knowledge, were only poorly developed. Furthermore, only participants in the younger group exhibited systematic explicit knowledge of the visuomotor rotations. Subsequent analyses revealed strong correlations between the quality of explicit knowledge and the overall visuomotor adaptation. Thus, visually cued dual adaptation to two opposite visuomotor rotations is primarily mediated by conscious strategic corrections based on explicit knowledge of the transformations, a process, which is selectively impaired in older adults.

Generalization of implicit and explicit adjustments to visuomotor rotations across the workspace in younger and older adults

We examined the generalization of adjustment to a visuomotor rotation across the workspace in younger and older adults. Participants practiced in the right workspace with a single target direction and were tested in both the right and left workspace with eight different target directions. A set of tests served to identify implicit and explicit components of adjustment. Explicit, but not implicit, components were stronger at younger than at older adult age. Explicit components generalized across all target directions, whereas implicit components were restricted to the target direction during practice and clockwise adjacent ones. Generalization to the contralateral workspace was found only for explicit components of adjustment. These findings expand the list of functional differences between implicit and explicit components of adjustment to visuomotor transformations.

Adaptation to a direction-dependent visuomotor gain in the young and elderly

Consistent with the widely accepted notion of separate specification of movement amplitude and direction, it has been argued that there is also a categorical difference between adaptation to novel visuomotor rotations and to novel visuomotor gains. In line with this view, ageing seems to affect rotation and gain adaptation differently in that age-related impairments are consistently found for the former, but not for the latter. In this study we ask whether the contrasting findings could also be ascribed to differences in the level of difficulty of gain and rotation adaptation tasks, respectively. In order to increase the difficulty of gain adaptation, younger and older participants had to adapt to a direction-dependent gain transformation. Results revealed direction-dependent adaptation in both groups. More importantly, we replicated the typical findings of age-related impairments of adaptation, but not of aftereffects, that were previously only reported for rotation adaptation. Younger participants also showed superior explicit knowledge regarding the novel visuomotor mapping as compared to the older participants. We show that this knowledge was used by younger participants to selectively augment adaptive shifts. Finally, our findings suggest that the difficulty of the novel visuomotor transformation and, related to this, the involvement of explicit knowledge in adaptation is critical for age-related changes to show up, but not the type of adaptation task, rotation and gain adaptation, respectively.

The Death of Handwriting: Secondary Effects of Frequent Computer Use on Basic Motor Skills

ABSTRACT The benefits of modern technologies such as personal computers, in-vehicle navigation systems, and electronic organizers are evident in everyday life. However, only recently has it been proposed that the increasing use of personal computers in producing written texts may significantly contribute to the loss of handwriting skills. Such a fundamental change of human habits is likely to have generalized consequences for other basic fine motor skills as well. In this article, the authors provide evidence that the skill to produce precisely controlled arm–hand movements is related to the usage of computer keyboards in producing written text in everyday life. This result supports the notion that specific cultural skills such as handwriting and typing shape more general perceptual and motor skills. More generally, changing technologies are associated with generalized changes of the profile of basic human skills.

Learning new visuo-motor gains at early and late working age.

Modern workplaces often require adaptation to novel visuo-motor transformations. Findings on age-related variations of such adaptation are rather inconsistent, suggesting that whether or not age-related impairments do occur depends on boundary conditions. This paper examined the hypotheses that age-related variations affect primarily strategic adjustments to novel transformations and can be found for complex (non-linear) transformations, but not for simple (linear) ones. After a practice period with linear and non-linear visuo-motor transformations, open-loop performance, after-effects and explicit knowledge were examined. Consistent with previous findings, older participants had longer movement times and shorter open-loop amplitudes, more so for long than for short target amplitudes. However, the study did not find any age-related variation of adaptation to a novel visuo-motor gain. Regarding adaptation to a non-linear transformation, the findings suggest slightly superior explicit knowledge of younger adults and the development of slightly more efficient closed-loop processes in the course of practice.

Implicit and explicit adjustments to extrinsic visuo-motor transformations and their age-related changes

Humans have unique abilities in using tools. The skilled and goal-directed use of a tool implies that processes of motor control can be adjusted to the transformation of the movement of a part of the body into the movement of the effective part of the tool. A common example is the transformation of a hand movement in the motion of a cursor on a computer monitor. In part the adjustments to such transformations are implicit, that is, without conscious awareness of the novel transformation and the appropriate change of ones own movements. However, the adjustments can also be explicit and intentional. We review a series of experiments which show that implicit and explicit adjustments to a novel visuo-motor gain are additive. This finding suggests that the processes which generate different types of adjustment are functionally independent. In a second series of experiments it turned out that at older adult age explicit adjustments to novel visuo-motor transformations are impaired, whereas implicit adjustments remain unaffected across working age.

Age-Related Variations of Visuomotor Adaptation Result From Both the Acquisition and the Application of Explicit Knowledge

The present study aimed to assess whether age-related differences in visuomotor adaptation are limited to the acquisition of explicit knowledge or extend to the application of the explicit knowledge in terms of deliberate strategic corrections. Old and young participants performed aiming movements, controlling a cursor on a computer screen with rotated visual feedback. Participants either received an explicit pretraining of the rotation or practiced a similar task that was unrelated to the upcoming rotation. Results show an age-related difference in the application of explicit knowledge and thereby extend previous findings of age-related differences in the acquisition of explicit knowledge.

Age-Related Variations in the Control of Electronic Tools

Electronic tools, such as a computer mouse, are highly flexible with respect to the visuo-motor transformations they implement. Different from mechanical tools, they lack mechanical transparency. Several studies noted difficulties of older users with computer-mouse operations, but also with more complex visuo-motor transformations as found in laparoscopic surgery. These difficulties may partly result from generalized slowing, but partly also from reduced learning capabilities. We explored the nature of the latter kind of change in a series of experiments.