P.C.W. van Wieringen

Coupling strength in tapping a 2:3 polyrhythm

The effects of tempo and role (fast vs. slow hand) on the reciprocal interaction (strength of coupling) between two hands tapping a 2:3 polyrhythm were examined from the perspective of nonlinear oscillator theory. A measure of the degree of harmonicity was developed, based on the relative contribution of the tapping frequency to the power spectrum of the limit cycle phase angle of each individual hand. On the assumption of fixed coefficients of the dissipative terms in the component oscillators, comparison of unimanual and bimanual performance with respect to this measure allowed for examination of the effects of the experimental conditions on the strength of the coupling. Five right-handed skilled drummers performed the 2:3 polyrhythm at several tempos and with both hand arrangements (i.e., either the preferred or the non-preferred hand tapped the faster cadence). The analysis revealed an inverse relation between tempo and coupling strength, and a larger influence of the fast hand on the slow hand than vice versa. No differences were observed between the two hand arrangements. The theoretical implications of these results were discussed in relation to similar and dissimilar findings in the literature.

Dynamics of reaching for stationary and moving objects: Data and Model

The nature of the interrelations among movement amplitude, movement time, and peak velocity was addressed in 2 experiments in which participants reached for stationary and moving objects. Movement time was found to scale with the distance between the hand and the object at the onset of movement but to be relatively independent of object speed. Peak velocity, however, was found to scale with both these variables. The origin of these interrelations cannot be understood within the framework of existing trajectory formation models that are based on optimization procedures. A dynamical perspective in which the movements are considered in an object-attached coordinate frame allows for their emergence. This is demonstrated by simulation of a nonlinear model, built up from Rayleigh and Duffing components, with the nonlinear dissipative parameter being associated with amplitude scaling.

Coordination in Prehension: information-based coupling of reaching and grasping

Abstract Prehension involves the coordination of a reaching and a grasping movement, such that the hand opens and closes in tune with the transport of the hand to the object to be grasped. To investigate this coordination, we focused on the transition from hand opening to hand closing in the grasping component of prehension. Earlier research has suggested that the time taken to close the hand remains constant over varying reaching amplitudes. In the present experiment, in which subjects reached for objects at six different distances and for objects that moved away from them at three different, constant speeds, hand-closure time was found to vary as a function of experimental conditions. Moreover, initiation of hand closure did not occur at a constant value of the (perceptually available) first-order time remaining until contact with the object. However, the variations observed, occurring as a function of initial hand-object distance and object speed, could be accounted for by an abstract dynamical model of perceptually driven postural changes.

The effect of video‐feedback on the learning of the tennis service by intermediate players

Effects of video-feedback on improvement of the tennis service were investigated in subjects having at least 2 years of playing experience in tennis. The experiment was carried out in an indoor tennis hall under normal training conditions. Subjects were randomly divided into three groups: a video-feedback training (VFT) group, a traditional training (TT) group and a control group, each consisting of 22 subjects. While the subjects of the control group received no training at all, subjects in both the VFT and TT groups were trained twice weekly during 5 consecutive weeks. Each training session lasted 40 min, of which 30 min was spent on actual practice in training of the service. The remaining 10 min was spent on watching, analysing and discussing video recordings of either their own service performed during the training session (VFT group), or ground strokes and volleys of top level players (TT group). Both the VFT and TT group showed significantly greater improvements in both achievement scores and form (technique) scores than did the control group. No differences, however, could be demonstrated between the VFT and TT group, indicating that the subjects of the former group did not benefit from the video-feedback they received. While form scores correlated significantly (P less than 0.001) with the velocity of the served ball, no such relation between form scores and spatial accuracy was apparent.

The effect of video‐modelling and video‐feedback on the learning of the tennis service by novices

This project is addressed to the effectiveness of video mediated instruction on the learning of the tennis service by novices. The research was carried out in an indoor tennis hall under normal training conditions. Three experimental groups were used: a video-model (VMT), a video-feedback (VFT) and a group with a combination of video modelling and video feedback (VMFT). Two control groups - based on different training periods-were also used: a traditional training group (TT1) which practised for a period of 45 min per training session and a second traditional training group (TT2) which practised for a period of only 30 min per training session. All subjects took part in five successive training sessions. No clear advantages of using video mediated instruction methods in teaching novices the tennis service could be demonstrated. Five sessions of 30 min practical training were shown to be as effective as five sessions of 45 min practical training in producing improvements in both form and achievement scores of novice tennis players. While, in the early stages, form and achievement scores were not shown to be significantly related, after five sessions a significant correlation (P less than 0.05) was shown.

The effect of manipulating knowledge of results on the learning of slalom-type ski movements

Three groups (N = 27 per group) of subjects were required to learn to make slalom-type ski movements under different conditions of instruction and related feedback utilizing a so-called ski-simulator comprising a platform moving over bowed rails. Training and test trials were repeated on each of four successive days (22·5 min per day of which 15 min were actually spent on practice). Subjects (dependent upon the group to which they were assigned) were instructed, during training trials, to direct their attention primarily to the frequency (tempo), the amplitude, or the fluency of the platform movement. Augmented feedback was provided only on that parameter. From the test results at the end of the fourth day, it was shown that the group which directed their attention during training to the amplitude of the movement of the platform were not only successful with respect to that parameter but also with respect to frequency and fluency (the three criteria defining the task). In contrast, the group which directe...

A Multidimensional Analysis of Some Persistent Problems in Motor Learning

Recent critiques of theories of motor learning (e.g. those of Adams (1971) and Schmidt (1976)) have centred around shortcomings with respect to their ability to account for such central issues as Bernsteins (1967) degrees of freedom problem and/or the problem of context conditioned variability (see for example Marteniuk & Romanow, 1983). A further problem has been the proposed existence of an executive capable of specifying various aspects of the movements to be produced. An alternative theory, currently attracting considerable attention, is that of action systems (Reed, 1982) in which the development of coordinative structures tuned to changing environmental demands without the need to invoke a command system has been central.

Assessment of aesthetic quality of artworks by expert observers: An empirical investigation of group decisions

Professional art experts were required to evaluate sets of ten to twenty slides of artworks created by young artists. The design of the experiment enabled comparisons between aesthetic quality judgements based on averaged scores of four to six experts and consensual judgements reached after discussions of the works within groups composed of the same four to six judges. It was demonstrated that the latter judgements often reflected the original evaluation of only one of the group members. Based on empirical considerations of both reliability and validity of judgements it was concluded that decisions about grants to young artists should be based on mean judgements by independent experts instead of on judgements reached during discussions between experts.

Dimensions of perception of posture in dance

Abstract This study reports a preliminary investigation designed to assess the possibility of using a semantic differential in the appraisal of expressive characteristics of posture in dance. Twenty still photographs of postures displayed by one female dancer were judged on 25 bipolar scales by 50 S s. Ratings of eight of these S s were used for estimating reliabilities of the scales — resulting in elimination of five scales. Intercorrelation matrices of the 20 remaining scales were obtained for each of the 42 remaining S s. Consideration of homogeneity of the distribution of these matrices led to the exclusion of four of them, leaving 38 matrices for further analysis. After random division of these matrices into two equally sized subgroups, principal component analyses with VARIMAX rotation were carried out on the average intercorrelation matrix for each subgroup. This resulted in two very similar three-factor solutions. The three factors, identified as similar to Osgoods well-known factors of activity, evaluation and potency, accounted for about 55% of the total variance. The results, discussed in terms of Berlynes conception, suggest that the semantic differential may be a reliable instrument for measuring connotations of posture in dance.

Vigilance performance and skin conductance

Abstract The relation is explored between vigilance performance and skin conductance level. A distinction is made between good and bad detectors. During the watch, performance and skin conductance of the good detectors remain constant; the bad detectors show a decrement on both variables. A second experiment is reported with a more complicated signal presentation (two types of signals). In comparison with the simples detection task (one type of signals) there is no difference in skin conductance, while detection and RT show less decrement in the more complicated task.