Reaction time in simultaneous motions

Changes in interhemispheric transfer rate and the development of bimanual coordination during childhood

In this study, we investigated the effect of the development of interhemispheric communication on age-related change in bimanual coordination. Interhemispheric communication was assessed by comparing the latency of a manual response to a visual stimulus when the hemisphere perceiving the stimulus and the hemisphere controlling the manual response were the same (uncrossed condition) to the latency when they were different (crossed condition). In the first experiment (5- to 10-year-old children) we used a two-choice response-time task, and in the second experiment (3- to 7-year-old children) we used a simple response-time task. In both studies, bimanual coordination was tested on a line-drawing task, and we compared performance on mirror and parallel movements. The crossed-uncrossed difference decreased with age in both experiments. When estimated on the simple response-time task, the crossed-uncrossed difference was related to the difference in performance between mirror and parallel movements on the bimanual task. Thus, improved interhemispheric communication contributes to progress in bimanual coordination, especially that which requires resisting the attraction of mirror movements in order to rotate both hands with parallel movements.

Structural constraints on bimanual movements

A theoretical framework is outlined, according to which structural constraints on bimanual movements can at least in part be understood as coupling between parameters of generalized motor programs. This framework provides a conceptual link between reaction-time data from experiments with bimanual responses, successive unimanual responses, and choice between left-hand and right-hand responses on the one hand and performance data obtained with concurrently performed continuous movements or sequences of discrete responses on the other. On the basis of data obtained with different methods for the study of intermanual interactions, a distinction is drawn between steady-state and transient constraints, and the hypothesis that the tendency to coactivate homologous muscles originates from a transient coupling of program parameters is applied to a variety of observations on performance in different tasks. Finally, the notion of transient constraints is applied to other types of intermanual interdependencies, and to interpersonal coordination; the possible emergence of transient constraints from steady-state constraints through progressive development of inhibitory pathways in childhood is discussed, as is the potential biological significance of transient constraints.

EMG-reaction time of the biceps brachii in bilateral simultaneous motions

EMG-RTs of the biceps brachii muscles were measured using electromyogram (EMG) in elbow flexion and forearm supination on 18 right-and 24 left-handed subjects for four tasks, flexion or supination (symmetrical) and flexion of one and supination of the other side (asymmetrical). For both subject groups, the EMG-RTs of flexion for both hands were not prolonged under asymmetrical tasks, but the EMG-RTs of supination were significantly prolonged on both sides. Comparing the coefficients of determination of the EMG-RTs of flexion to those of supination under four different tasks, those of the preferred hand for symmetrical and asymmetrical motions did not differ, but those of the nonpreferred side for asymmetrical motions were smaller than those for symmetrical motions in both subjects. These observations indicated prolongation of EMG-RT on the asymmetrical task was larger on supination than on flexion. It was suggested that the influence of strong timing constraints was greater on the auxiliary function than on the innate function of the biceps (elbow flexor). The steadiness of motor function of the preferred hand was also discussed in regard to hand preference.

Target-Size Influences on Reaction Time with Movement Time Controlled

The variable that affect motor programming time may be studied by changing the nature of the response and measuring the subsequent changes in reaction time (RT). One notion of motor programming suggests that aiming responses with reduced target size and/or increased target amplitude require more "complex" motor programs that require longer RTs. In a series of five experiments which movement time (MT) was experimentally varied target size neither influences RT when the movement amplitude was 2 or 30 cm nor when the target sizes differed by as much as a factor of 16:1. Increasing the movement amplitude from 15 to 30 cm also had no influence on RT. Movement time, however, did affect RT, with 200-msec movements having longer RTs than 120-msec movements. Target size and movement amplitude did not appear to be factors that influence programming time or program complexity.