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Use of different effectors in two consecutive actions could generate an attentional shift between the effectors with shorter latencies in the second action of reaching. 18 participants (10 men; M age = 21.3 yr.) participated in an experiment with two main variables: (1) effector switching with two levels (Switching and No Switching), where the participants use or do not use a different motor effector for each action; (2) lifting muscles, i.e., the muscles involved in the first phase of the reaching, with two levels (finger-lifting muscle and palm-lifting muscle). Premotor time, Motor time, Reaction time, Movement time, and Total time were measured. For Premotor, Movement, and Total times, faster responses were observed when there was no switching of the effector. This delay could be due to an attentional shift between motor effectors and its relations with motor processes. Possible applications include the ergonomic design of device controls, considering that the use of the same effector is beneficial when fast reaction times are sought.

The effects of stimulus-response compatibility and response preparation on the motor component of the information processing system were investigated by analyzing the fractionated reaction time for the upper and lower limbs. The reaction time was divided into two periods with respect to the onset of electromyographic activity, premotor and motor times. The response preparation was manipulated by the probability that the locations of the precue and subsequent imperative stimulus corresponded. On a stimulus-response compatible task, subjects were required to release a key on the same side as an imperative stimulus, irrespective of the precued side. On an incompatible task, subjects were required to act in the reverse manner. The upper and lower limb responses were measured during both tasks. A repeated-measures design was used with 12 male university students. Analysis of the reaction and premotor times indicated that the stimulus-response compatibility effect became larger as response preparation decreased. The analysis of motor time yielded significant interactions between stimulus-response compatibility and limb and between response preparation and limb. These findings indicated that the motor component of information processing for the lower limb response is affected by both stimulus-response compatibility and response preparation.

We measured the fractionating reaction time for upper and lower limbs of 18 young men, using an electromyogram to clarify the interaction of response preparation and stimulus-response congruence on premotor and motor time. The reaction time was divided into two periods with respect to the onset of the electromyogram, premotor and motor components. Manipulating the probability of the Go versus NoGo signals varied three different amounts of response preparation. Prior to the imperative stimulus, precue information about the position of a stimulus was presented. In the stimulus-response congruent task, subjects were required to release a key on the same side of the body using either an upper or lower limb in response to an imperative Go stimulus. In the stimulus-response incongruent task, subjects were required to act in a reverse manner. Subjects were not supposed to respond to the NoGo stimulus. The premotor time of the upper and lower limb responses was affected by the respective effects of response preparation and stimulus-response congruence. The motor time of the upper and lower limb responses increased as the probability of the Go signal decreased but not in relation to stimulus-response congruence. These results suggest that response preparation affects not only information processing time but also peripheral motor activity due to motor programming, and that the stimulus-response congruence effect on motor time disappears when information about the position of the imperative stimulus is precued.

In a previous study, Ito (1990) who used a rapid two-element force-production task, found that the simple reaction time (RT) to initiate the second element was shorter when a sequence was made up of homogeneous elements than when a sequence was made up of heterogeneous elements. The purpose of the present study was to replicate and extend the earlier experiment by adding a control condition and by fractionating RT into premotor time and motor time. Simple RT, premotor time, and motor time to initiate the first element were not different across conditions, suggesting the possibility of distributed programming of the sequence elements. The homogeneous condition, however, produced shorter simple RT and premotor time to initiate the second element than did the heterogeneous and control conditions, which were not significantly different from each other. These findings were discussed in terms of different programming demand during the RT interval.

This study investigated the effect of circumferential pressure on timing and muscle-response parameters during ballistic ankle plantar flexion in 15 young healthy subjects. Circumferential pressure was provided by an air-splint applied around the lower calf. Data were collected at 1, 3, and 5 min. prior to, during, and following application of pressure. A 3 × 3 repeated-measures analysis of variance indicated significant increases in premotor and reaction times during application of pressure. There was no main effect for magnitude of muscle activity or motor time. Results support previous studies showing decreases in the excitability of the motor-neuron pool with circumferential pressure and an inverse relationship between excitability and premotor time.

Summary.-The present study was designed to investigate the effect of speed and accuracy of force exertion on the relationship between force output and fractionated reaction time. Subjects exerted their force (10% or 40% of maximum isometric contraction) on "accurate" and "fast" tasks as rapidly as possible at the light signal. On the "fast" task, premotor time for the 40% target was lengthened in comparison with that for the 10% target, and motor time was shortened with an increase of force output. On the "accurate" task, on the other hand, premotor time was independent of magnitude of force, and no relation between motor time and force output was found. These findings show chat the relationship between force output and fractionated reaction time may be affected by the effort to exert force accurately. Fractionated reaction time as a function of force output has been studied by several investigators. Morris (1977), Wood (1979), and Kamen, Kroll, Clarkson, and Ziegon (1981) measured premotor time using the resistance of an electromagnet; the resistance was only 5 to 25% of the maximum voluntary isometric contraction. According to them, there was no difference between premotor times under resisted and unresisted conditions. Baba and Marteniuk (1983) also reported that premotor and motor reaction times were not affected by an increase in torque. The task used in their experiments was a rapid flexion of elbow whose inertia was increased by 50% by adding mass to the arm support apparatus. Haagh, Spijkers, van den Boogaart, and van Boxtel (1987) found that prernotor time was negatively related to peak force amplitude. In their experiments, subjects exerted force by squeezing a force transducer between the right thumb and index finger under the three conditions with 5, 25, and 50% of the maximum voluntary isometric strength. On the other hand, we reported that premotor time for the heavy load was lengthened in comparison with that for the light load when two different weights (10 and 40% of maximum voluntary isometric contraction) were applied to the elbow joint (Kawabe, 1987, 1989). Nagasaki, Aoki, and Nakamura (1983) also reported that prernotor time in elbow extension increased with an increase in force output; however, the magnitude of the muscle strength in their experiment was arbitrarily defined. In the results, there was an inconsistency in the effect of force output

The present study assessed differences in stimulus-response compatibility effects during central information processing and peripheral motor control between upper and lower limbs by measurement of times for premotor and motor response to a stimulus presented to one visual hemifield. 16 subjects participated. One stimulus-response assignment was Compatible and the other was Incompatible. In the former, the stimulus presented in the left field required a response from a left limb, and that presented in the right field required a response from a right limb. In the Incompatible condition, assignments were reversed. For both conditions, subjects were required to release the key for the upper or the lower limb as quickly as possible. The analysis of Premotor time showed the stimulus-response compatibility effect for both upper and lower limb responses, although analysis of Motor time indicated the stimulus-response compatibility effect occurred in only a lower limb response. It is concluded that the effect of stimulus-response compatibility for upper limb response was influenced only by central information processing, while the effect for lower limb response was influenced also by peripheral motor control.

Ten hemiplegic subjects completed 20 rapid dorsiflexions of their afflicted and nonafflicted limbs. Electrodes were attached to the tibialis anterior and the gastrocnemius muscles and electromyograms were recorded for their premotor time, motor time, and simple reaction time during ankle dorsiflexion and plantar flexion of their lower limbs. The fractionated components of reaction time, namely, premotor time and motor time, of both legs were statistically compared. It was found that the premotor time of the subject's stroke-affected limb was significantly slower than the premotor time of the nonaffected limb (control), with no differences between their associated mean motor times. These results supported the hypothesis that a stroke has a deleterious affect upon the central, premotor time processing centers and has no disruptive influence upon the peripheral motor time. Comparing the fractionated components of reaction time (premotor time and motor time), with simple reaction time, the former provided a more sensitive and valid method to detect possible injurious side effects of a stroke upon the brain's neuromotor transmission centers and subcenters, and their peripheral, stimulus, response network.

Eight male smokers were tested under 6 conditions comprising the combinations of 200 mg. caffeine or no caffeine, with no cigarette, one 0.3-mg. nicotine cigarette or one 1.3-mg. nicotine cigarette, for decision time and motor time scores on a choice reaction-time task. Heart rate was monitored from a pretest period throughout the session, and hand steadiness measured on repeated occasions. Decision-time scores were significantly decreased by both caffeine and nicotine, but no interaction was found. The high-nicotine cigarette had the greatest effect. Motor time scores were improved by caffeine only. Both caffeine alone and nicotine alone accelerated the heart rate but in combination appeared to have antagonistic effects. Hand steadiness was significantly impaired by both drugs but with no interaction.