A mental route to motor learning: Improving trajectorial kinematics through imagery training

Abstract

There are contrasting reports upon the level of effectiveness of motor imagery in learning new motor skills, but there is general consensus that motor imagery can lead to improvements in performance, especially in combination with physical practice. In the present study we examined the effectiveness of motor imagery in the acquisition of movement invariants in two grapho-motor trajectorial learning tasks with differing visuospatial components: `Ideogram drawing' and `connecting circles'. Two subject groups were studied: An imagery group, which underwent 10 min of motor imagery training and a control group, which practised a control visuomotor task over the same period of time. The results showed that imagery training alone enabled the subjects to achieve a significant approach to movement isochrony as well as a significant shifting of peak velocity toward the target. After a practice phase, both groups improved their performance, but the imagery group was still significantly faster than the control group. Furthermore, a series of tests measuring visual imagery abilities was administered to the subjects. There were however no significant relationships between the motor performance and the visual imagery ability levels of the subjects. It is concluded that motor imagery can improve the acquisition of the spatio-temporal patterns of grapho-motor trajectories and that there are different processes involved in visual and motor imagery.

Introduction

Motor learning has been traditionally defined [36]as the acquisition of skilled movements as the result of practice, specifically of physical practice. Motor learning, however, can also be understood as the acquisition of the required temporal and spatial characteristics of movements. During such an acquisition phase, the motor programme for the execution of the movement is modified and consolidated.

One of the many sub-processes that may exert a certain contribution to motor learning is motor imagery. Neurophysiological relationships between imagining and actually performing a movement have indeed been demonstrated using brain activity mapping techniques such as PET e.g. 13, 30, 7, 37, 41, 38and fMRI 19, 31. These findings support the notion that the cortical areas activated during the imagination of a movement are very similar to those activated during its performance. Thus, it seems logical to expect that the central changes produced during motor imagery should also have an effect on the motor performance. Although it has already been shown in a remarkable number of studies that the use of mental practice for the learning of a motor task produces significantly greater improvements than no practice at all, e.g. 25, 40, 33, 48. Mental practice in this context refers to `the symbolic rehearsal of a physical activity in the absence of any gross muscular movements' [29]. However in some studies positive effects of imagery training could not be achieved 2, 11, 39, 32. Yet in other studies the combination of both mental and physical practice was found to produce the best results 42, 5, 20, 46.

Thus it is possible to conclude that despite more than six decades of research on the topic there is no consensus as to whether imagery training leads to improvements in the acquisition or performance of motor skills. The great variation in task selection, group selection, method of imagery training and a host of other factors may account for the differing results. It appears necessary to study mental practice further and in particular to consider the mechanisms involved in the contribution of mental practice to motor learning. For this purpose in the present study a verbal and visuospatial imagery questionnaire and a battery of imagery and working memory tests were administered to the subjects in the present study of mental practice of trajectorial learning.

To our knowledge imagery training has not yet been applied to trajectorial learning, a procedural skill which should not be open to introspective or declarative reasoning and which therefore should not be able to be influenced by the verbal components of imagined practice. The visuospatial components of imagery should however contribute to learning and should lead to some improvement in skill acquisition. In order to evaluate the contribution of visuospatial imagery in this context, two trajectorial learning tasks with differing visuospatial and graphomotor components were chosen: `Ideogram drawing' and `connecting circles'. It was assumed that the visuospatial differences between these tasks would far out-weight any differences in demands upon central processes of motor learning, although these latter could of course not be held constant.