The difference in RT for right and left biceps, acting on the forearm in two different movement patterns, flexion and supination, was examined for 14 normal Ss, seven right-handed and seven left-handed. The task was to flex or supinate both forearms simultaneously in response to a sound stimulus. Median RTs of each S were computed for each movement task. The analysis indicated that RT of supination is faster than that of flexion. Concerning left-right difference of RT, the flexion of the non-preferred hand is faster than that of the preferred hand and the supination of the preferred hand is faster than that of the non-preferred hand. Even in a simple movement there are differences in RTs for the right and left hands which do not depend on the muscles but on the movement patterns. Hemispheric dominance is not established by comparing the rapid initiation of movement.
EMG reaction times (EMG-RTs) of triceps brachii muscle of normal subjects and patients with focal brain lesions were measured at two different positions of the shoulder joint. The difference of EMG-RTs between the two positions was smaller in patients with VL-thalamotomy, cerebellar or frontal premotor lesions than in normal subjects and patients with hemiplegia. It is assumed that cerebellum, VL-nucleus and the premotor area are related to the proprioceptive control of RTs.
RT and its left/right difference of both biceps muscles were measured by electromyogram (EMG) in the bilateral simultaneous flexion of elbows using 11 left- and 13 right-handed subjects under four conditions which were combinations of two factors; warning signal; presence or absence of a fore-period, and position of limbs; elbow 90 degrees or 135 degrees. EMG-RT and its left/right difference were influenced by these factors. The effects of warning and position of limbs were not the same on the preferred and non-preferred hands. It was assumed that EMG-RTs of biceps in the preferred hand were less influenced by these experimental conditions.
Using 7 left- and 7 right-handed subjects, the difference in time between left and right arms in the initiation of bilateral simultaneous flexion of elbows (synchronization error) was measured under three conditions: response to a sound stimulus with a warning signal, response to a sound stimulus without a warning signal, and self-initiated trial (option). The absolute value of synchronization errors depended upon experimental conditions. In conditions 'with warning' and 'option' the dominance shown in performance of left-handed subjects was the mirror-image of that shown by the right-handed subjects. The right biceps muscle responded faster in left-handed subjects and vice versa. Right-handed subjects showed rather a constant value in their dispersion of synchronization errors.
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