Sandra Sülzenbrück

Functional independence of explicit and implicit motor adjustments

Adaptation to novel visuomotor transformations for example when navigating a cursor on a computer monitor by using a computer mouse, can be explicit or implicit. Explicit adjustments are made when people are informed about the occurrence and the type of a novel visuomotor transformation and intentionally modify their movements. Implicit adjustments, in contrast, are made without reportable knowledge of a novel visuomotor transformation and without a change intention. The relation of implicit adjustments to explicit adjustments needs further clarification. Here we show that these two types of adjustment occur at the same time and remain functionally independent. The size of total adjustment turned out to be the sum of explicit and implicit adjustments measured in isolation, even when both processes produce opposite outcomes. In perspective our results demonstrate that automatic, implicit processes of motor control are not superseded by intentional, explicit ones, but only superposed.

Learning the visuomotor transformation of virtual and real sliding levers: simple approximations of complex transformations

Learning to operate a complex tool such as a sliding lever can be conceived as learning both a kinematic and a dynamic transformation. We investigated whether the presence of the dynamic transformation has an inhibitory or a facilitative effect on learning to control a sliding lever. Furthermore, we examined the characteristics of the internal model of the kinematic transformation of the lever in visual open-loop trials. In the experiment, one group of participants practiced with only the kinematic transformation of the lever (virtual lever), the other group practiced with both the kinematic and the dynamic transformation (physical lever). Visual feedback was continuously present during practice. Results showed only marginal differences between both groups in open-loop tests. This finding is likely to be related to the fact that in both groups a simplified approximation of the kinematic transformation was acquired, in particular a symmetry approximation. With such an approximation the target for the hand movement is derived from the visual target for the tip of the lever as the position which is symmetric around a sagittal axis.

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.

Type of visual feedback during practice influences the precision of the acquired internal model of a complex visuo-motor transformation

This study investigated the influence of the type of visual feedback during practice with a complex visuo-motor transformation of a sliding two-sided lever on the acquisition of an internal model of the transformation. Three groups of participants, who practised with different types of visual feedback, were compared with regard to movement accuracy, curvature and movement time. One group had continuous visual feedback during practice and two groups were presented terminal visual feedback, either only the end position of the movement or the end position together with the trajectory of the cursor. Results showed that continuous visual feedback led to more precise movement end positions during practice than terminal visual feedback, but to less precise movements during open-loop tests. This finding indicates that terminal visual feedback supports the development of a precise internal model of a new visuo-motor transformation. However, even terminal feedback of the cursor trajectory during practice did not result in an internal model, which includes appropriate curvatures of hand movements. Statement of Relevance:This paper presents results on the influence of type of visual feedback on learning the complex motor skill of controlling a sliding lever. These findings contribute to the conceptual basis of optimised training procedures for the acquisition of sensori-motor skills required for the mastery of instruments utilised in minimally invasive surgery.

Trajectories in Operating a Handheld Tool.

The authors studied the trajectories of the hand and of the tip of a handheld sliding first-order lever in aiming movements. With this kind of tool, straight trajectories of the hand are generally associated with curved trajectories of the tip of the lever and vice versa. Trajectories of the tip of the lever exhibited smaller deviations from straight paths than did trajectories of the hand, even though the cursor, which displayed the position of the tip of the lever on a computer monitor, was invisible during movement execution. These observations suggest that movement of the effective part of the tool is the primary kinematic variable in motor planning and control, even in the absence of continuous visual feedback. The presence of continuous visual feedback did not change the basic pattern of results, except that the remaining deviations from straight paths of the tip of the lever became smaller. These deviations most likely result from an inertial anisotropy of the tool, and they are reduced by visually based online corrections.

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.

The trajectory of adaptation to the visuo-motor transformation of virtual and real sliding levers.

We studied adaptation to the visuo-motor transformation of a virtual and a real two-sided sliding lever. In a previous study (Sülzenbrück and Heuer in Exp Brain Res 195:153–165, 2009) we had found essentially no differences. However, adaptation had been restricted to a simplified symmetry approximation of the transformation. In the present study practice conditions were designed to facilitate adaptation (e.g., terminal rather than continuous visual feedback). In visual open-loop tests, differences between the effects of practice with a virtual and a real lever were found for curvature of hand movements, whereas movement end positions were not different. Curved hand movements induced by the use of the real lever persisted in subsequent open-loop tests with the virtual lever. Early in practice end-position errors were strongly biased toward the simplified symmetry approximation, but this bias was reduced later on. Thus, the symmetry approximation is a transient state in the trajectory of adaptation that is reached quickly and from which there is a slow and gradual transition to an accurate internal representation of the visuo-motor transformation of the sliding lever.

Enhanced mechanical transparency during practice impedes open-loop control of a complex tool

We investigated the impact of enhanced mechanical transparency during practice on closed-loop performance as well as on the acquisition of an internal representation of the visuo-motor transformation of a lever. Three groups of participants controlled a cursor on a monitor by moving the effort arm of a sliding two-sided lever. The level of mechanical transparency was manipulated by varying the amount of conceptual knowledge about the tool the participants were using as well as by the visualization of the effective part of the tool on the monitor. While for groups cursor− and cursor+ only a cursor representing the tip of the load arm of the lever was visible, group shaft was additionally provided with a representation of the load arm on the monitor. The cursor groups differed in conceptual knowledge about the tool, with only group cursor+ being informed that they were controlling a two-sided lever. Enhanced mechanical transparency, resulting from the visibility of the lever arm, boosted performance in terms of faster and straighter movements when concurrent visual feedback was available, and therefore closed-loop control was possible. In contrast, a detrimental effect of enhanced mechanical transparency during practice on the accuracy of the internal representation of the visuo-motor transformation was observed. When assessing open-loop control in test trials without visual feedback, participants who had previously practiced the tool transformation with the visible lever arm showed larger end point errors than those who had practiced with the cursor only. These findings support the notion that enhanced mechanical transparency of a tool is a type of environmental support which boosts closed-loop performance, but impedes open-loop performance, most likely by serving as a substitute for an internal representation. When practice conditions facilitate closed-loop control, the acquisition of an accurate internal representation of a novel visuo-motor transformation seems to be hampered.

Generalized slowing is not that general in older adults: Evidence from a tracing task

One of the fundamental concomitants of aging is generalized slowing of almost all motor and mental functions. The present study aimed to elucidate the generality of slowing across different sensorimotor tasks. Results show that although slowing can be found in many tasks, older adults perform faster in a tracing task compared to their younger counterparts. Potential explanations of these findings are discussed with respect to biological changes in the course of aging and with respect to cultural and technological developments during the last decades.

Mind and movement

Voluntary movements embrace both intentional, conscious and post-intentional, largely automatic processes. Here, we examine these types of processes and the relations between them during preparation and execution of voluntary movements. First, a general overview is given about how intentional and post-intentional components are interleaved to enable successful control of purposeful movements. Second, we briefly describe some post-intentional processes that are triggered by preceding intentions. Third, we discuss findings according to which such post-intentional processes or their results can become accessible to conscious awareness. Under such conditions, automatic and conscious processes can co-occur. We show that intentional interventions into post-intentional processes can be overridden by automatic processes, can interfere with automatic processes and can be independent so that their outcomes add to those of automatic processes.