Effects of time uncertainty and instructed muscle tension on fractionated reaction time

Abstract: An experiment was conducted to examine the effects of time uncertainty and instructed muscle tension on the reaction time of elbow flexion. Twenty-two right-handed subjects were asked to respond to an audio stimulus by flexing their right elbow under four conditions (2 time uncertainty × 2 instructed muscle tension). Electromyograms (EMGs) were recorded from the biceps and triceps on the subject's right side. Reaction time was divided into premotor time and motor time, based on the difference between the EMG and elbow flexion response. Analysis of reaction time showed that the effects of time uncertainty and instructed muscle tension were additive. Time uncertainty affected premotor time only, and instructed muscle tension affected motor time only. These results are discussed in terms of the assumption that premotor time is a reflection of the central nervous system and motor time is a reflection to the peripheral muscle system.     

Effects of Fatigue and Laterality on Fractionated Reaction Time

Surface EMG enabled fractionation of a simple hand grip total reaction time into peripheral and central processing components (motor time and premotor time, respectively). Changes in reaction time components were investigated in 12 female intercollegiate swimmers (bilateral athletes) and 12 female intercollegiate tennis players (unilateral athletes) following a 48% strength decrement induced by serial maximal voluntary isometric contractions (5 sec in duration). Despite significantly greater strength in the dominant arm than in the nondominant arm, there was no difference in fatigue effects between arms. Fatigue increased the premotor component of reaction time significantly, and indirectly the total reaction time, but the motor time remained essentially constant regardless of the type of previous athletic training. This indicated that fatigue impaired central nervous system or myoneural-junction operations rather than the intramuscular ability to initiate force.     

Effects of fatigue and laterality on fractionated reaction time

Surface EMG enabled fractionation of a simple hand grip total reaction time into peripheral and central processing components (motor time and premotor time respectively). Changes in reaction time components were investigated in 12 female intercollegiate swimmers (bilateral athletes) and 12 female intercollegiate tennis players (unilateral athletes) following a 48% strength decrement induced by serial maximal voluntary isometric contractions (5 sec in duration). Despite significantly greater strength in the dominant arm than in the nondominant arm, there was no difference in fatigue effects between arms. Fatigue increased the premotor component of reaction time significantly, and indirectly the total reaction time, but the motor time remained essentially constant regardless of the type of previous athletic training. This indicated that fatigue impaired central nervous system or myoneural-junction operations rather than the intramuscular ability to initiate force.     

Premotor and Motor Reaction Time as a Function of Preliminary Muscular Tension

Ss squeezed a hand grip device to 1 of 3 submaximal tensions, and reacted to either a light (Exp. I, N = 30) or to a buzzer (Exp. II, N = 24) by squeezing as quickly and forcefully as possible. Total RT was the time from stimulus to the change in tension, and this was divided into Premotor RT (stimulus to change in EMG) and Motor RT (change in EMG to change in tension) to determine the locus of changes in Total RT found by Clarke (1968). Whereas Total RT was unaffected by increased pre-tension, Premotor RT shortened and Motor RT lengthened. Partial programming or activation hypotheses were tenable for the Premotor RT changes, whereas changes in the contractile component, but not in the series elastic component, were tenable for the Motor RT changes.     

Differences in the transmission of sensory input into motor output between introverts and extraverts: Behavioral and psychophysiological analyses

The present study was designed to investigate extraversion-related individual differences in the speed of transmission of sensory input into motor output. In a sample of 16 introverted and 16 extraverted female volunteers, event-related potentials, lateralized readiness potentials (LRPs), and electromyogram (EMG) were recorded as participants performed a visual choice reaction time task. As additional behavioral indicators of performance, measures of reaction time (RT) and response dynamics were obtained. Although extraversion-related differences were found neither for behavioral measures nor for the N1 and P3 components of the evoked potential, introverts showed a reliably shorter latency in stimulus-locked LRP than extraverts. This latter finding supports the notion of faster stimulus analysis in introverts compared to extraverts. Furthermore, there was no indication of extraversion-related individual differences in speed of response organization and response execution as indicated by response-locked LRP and EMG latencies, respectively. However, a significantly higher EMG amplitude observed with introverts pointed to a less accurately adjusted motor output system of introverts compared to extraverts.     

Identification of sensorimotor components accounting for individual variability in Zahlen–Verbindungs-Test (ZVT) performance

The Zahlen–Verbindungs-Test (ZVT) represents a highly feasible measure of information-processing speed that correlates quite highly with standard psychometric tests of intelligence. The present study was designed to identify specific stages of the sensorimotor processing system that may account for individual differences in overall variability of ZVT performance. For this purpose, ZVT, reaction time (RT), lateralized readiness potential (LRP), and electromyogram (EMG) measures were obtained in 48 female participants. While faster RT, smaller intraindividual variability in RT, shorter response-locked LRP and EMG latencies were associated with superior ZVT performance, speed of stimulus analysis, as reflected by stimulus-locked LRP latency, was unrelated to ZVT performance. Additional commonality analyses suggested a functional relationship between ZVT performance and the time course of central aspects of response organization rather than the time required for execution of the overt motor response. These findings provide converging evidence for the general notion of an association between speed of motor processing and intelligence.     

Emotional responding following experimental manipulation of facial electromyographic activity

Increases in zygomatic electromyographic (EMG) responding have been reported during the imagination of positive affective scenes, and increases in corrugator EMG have been reported during negative affective scenes. Thirty female subjects were instructed to imagine three positive affective scenes and three negative affective scenes. During the initial imagination of each scene, the subject was told simply to imagine the situation. The subject then imagined the situation again and was instructed to enhance the muscle tension in one of two muscle groups (the zygomatic muscles for positive scenes and the corrugator muscle for negative scenes). The subject then imagined the scence a third time and was instructed to suppress the muscle tension in the same muscle group. The order of administration of enhancement and suppression trials was randomized for each scene. Subjects were given several trials to practice controlling both zygomatic and corrugator EMG. Feedback was available during the practice trials and during the enhancement and suppression trials of the experiment. Continuous monitoring of both zygomatic and corrugator EMG during the study indicated that subjects were successful in altering muscle tension in accord with the experimental instructions, and videotapes of subjects' faces indicated no overt changes in facial responding during imagination of the scenes. Subjects' ratings of emotional responding during each scene indicated that subjects experienced less enjoyment and more distress during positive affective trials in which they suppressed zygomatic EMG activity. The results are discussed in terms of the facial feedback hypothesis.     

Contingent muscular tension during a choice reaction task

This study examined the effects of contingent muscular tension on a choice reaction task, and especially, the effects various amounts of muscular tension have on the information processing of choice reaction time. The reactive movement task included a choice reaction task. Ten right-handed healthy men (ages 18 to 19 years) underwent trials with stimulus presentation probabilities of 50% and 20% on the muscular tension task and choice reaction tasks. The conditions for the muscular tension tasks were divided into seven different conditions: 0%, 10%, 20%, 30%, 40%, 50%, and 60% of maximum voluntary contraction. On these tasks, subjects performed isometric contraction of the biceps brachii. The choice reaction task was a rapid extension of the left or right knee as a choice reaction. Measures were choice reaction time, movement time, and total reaction time. Analysis indicated that shortening choice reaction time of the left and right feet was observed under 10% muscular tension of maximum strength. Muscular tension appreciably influenced information processing, including choice reaction time. Muscular tension did not affect movement time. Results are discussed with respect to previous research and the optimal muscular tension for best performance.     

Cardiac modulation of startle: Effects on eye blink and higher cognitive processing

Cardiac cycle time has been shown to affect pre-attentive brainstem startle processes, such as the magnitude of acoustically evoked reflexive startle eye blinks. These effects were attributed to baro-afferent feedback mechanisms. However, it remains unclear whether cardiac cycle time plays a role in higher startle-related cognitive processes, as well. Twenty-five volunteers responded first by ’fast as possible’ button pushes (reaction time, RT), and second, rated perceived intensity of 60 acoustic startle stimuli (85, 95, or 105 dB; 50 ms duration; binaural; instantaneous rise time), which were presented either 230 or 530 ms after the R-wave, and eye blink responses were measured by EMG. RT was divided into evaluation and motor response time according to previous research. Increasing stimulus intensity enhanced startle eye blink, intensity ratings, and RT components. Eye blinks and intensity judgments were lower when startle was elicited at a latency of R + 230 ms, but RT components were differentially affected: the evaluative component was attenuated, and the motor component was accelerated when stimuli were presented 230 ms after the R-wave. We conclude that the cardiac cycle affects the attentive processing of acoustic startle stimuli.     

Periodicity within reaction time distributions and electromyograms

This study investigates a periodic component in reaction time frequency distributions, that is, a tendency for responses to occur at regular, discrete intervals of time after stimulus presentation. Reaction time frequency distributions were plotted by a Computer of Average Transients and were obtained under stimulus conditions varying in sense modality stimulated (auditory and visual), and the intensity, colour, and duration of stimulation. The results indicated that there was periodicity in reaction time frequency distributions with a modal period of approximately 25 msec. It was found that the periodicty (a) was most evident when there was considerable variability in reaction time, and (b) tended to attenuate when a large number of reaction times were grouped. Other stimulus conditions appeared to have little effect on the periodicity. A significant correlation was found between the frequency of periodicity in the reaction time distributions and the electromyograms, both having a modal period of 25 msec. It was concluded that the periodicity in reaction time was the result of motor processes.     

Extroversion-related differences in speed of premotor and motor processing as revealed by lateralized readiness potentials

To further elucidate extroversion-related differences in speed of sensorimotor processing, the authors obtained behavioral and psychophysiological measures as participants (16 introverts and 16 extroverts) performed a visual go/no-go task. Although no extroversion-related differences in reaction time emerged, introverts showed faster premotor processing but slower central and peripheral motor processing--as indicated by latencies of the lateralized readiness potential (LRP) and electromyographic (EMG) data, respectively--than extroverts did. Additional regression analyses revealed that stimulus-locked LRP latency, response-locked LRP latency, and Nl EMG amplitude accounted for 40% of overall variability in individual extroversion scores. On the basis of the present results, the authors introduce a compensation hypothesis that accounts for the common failure of researchers to demonstrate extroversion-related differences in reaction time. The present results challenge J. Brebner and C. Cooper's (1985) model of extroversion in which stimulus analysis is not slower in introverts than in extroverts. However, the present findings support the assumption of faster motor processing in extroverts.     

Effects of nonconscious perception on motor response

The present study reviews the literature on the empirical evidence for the dissociation between perception and action. We first review several key studies on brain-damaged patients, such as those suffering from blindsight and visual/tactile agnosia, and on experimental findings examining pointing movements in normal people in response to a nonconsciously perceived stimulus. We then describe three experiments we conducted using simple reaction time (RT) tasks with backward masking, in which the first (weak) and second (strong) electric stimuli were consecutively presented with a 40-ms interstimulus interval (ISI). First, we compared simple RTs for three stimulus conditions: weak alone, strong alone, and double, i.e., weak plus strong (Experiment 1); then, we manipulated the intensity of the first stimulus from the threshold (T) to 1.2T and 2T, with the second stimulus at 4T (Experiment 2); finally, we tested three different ISIs (20, 40, and 60 ms) with the stimulus intensities at 1.2T and 4T for the first and second stimuli (Experiment 3). These experiments showed that simple RTs were shorter for the double condition than for the strong-alone condition, indicating that motor processes under the double condition may be triggered by sensory inputs arising from the first stimulus. Our results also showed that the first stimulus was perceived without conscious awareness. These findings suggested that motor processes may be dissociated from conscious perceptual processes and that these two processes may not take place in a series but, rather, in parallel. We discussed the likely mechanisms underlying nonconscious perception and motor response to a nonconsciously perceived stimulus.     

Human locomotor adjustments during perturbed walking

The locomotor adjustment induced by step perturbation of human subjects walking on a treadmill was described by a quantitative analysis of the EMG activities of selected trunk and leg muscles and by rotations of leg joints. The role of the proprioceptive input in the EMG reaction was also evaluated. The perturbation was obtained by a rapid and unexpected increase of belt speed. The motor response showed the stereotyped characteristics of a motor automatism and was accomplished without affecting the basic motor pattern of the gait. The EMG adjustment showed short-latency reflex responses (40–60 msec) of muscles acting at the joints more directly affected by the perturbing stimulus. This result supports the hypothesis of a spinal neuronal mechanism involved in the rapid adjustment of gait. The activity of primary spindle afferents seems to play an important role in the production of the faster EMG responses.     

Ear differences in simple reaction time: The influence of attentional factors

Simple motor reaction times (right-handed) to tape-recorded consonant-vowel syllables were obtained from 12 subjects under two conditions of monotic stimulation: “expected” presentation (subject informed as to ear of presentation) and “random” presentation (ear of presentation varied randomly). Significantly faster left ear reaction times were obtained in the “expected” condition. The rank order of subjects' standard dichotic listening task scores correlated negatively with reaction time ear differences in the “expected” presentation condition. Results are discussed in terms of existing theories of response lateralization in simple reaction time tasks, and an expanded hypothesis is offered. Specifically, it is suggested that two or more distinct but potentially overlapping mechanisms may be responsible for observed asymmetries in monotic auditory perception. Both an attentional or lateralized motor response bias and an inherent lateralization of function may operate side by side, differentially activated by task demands, mode of stimulus presentation, and nature of stimuli.     

Perceptual and motor components of performance in three different reaction time experiments

Three reaction time experiments were conducted to examine the effects of time of day, stimulus intensity, stimulus modality, and constant and variable foreperiod on the perceptual and motor components of performance. These variables are all supposed to generate changes in arousal level. All the independent variables affected the perceptual component, while the motor component was significantly influenced only by foreperiod and modality. The results are discussed in relation to aspects of dependency/independency of the perceptual and motor components of human performance in reaction time experiments.     

Development of muscle fatigue assessed by using superposition of evoked and volitional myoelectric potentials.

We studied muscle fatigue development using evoked myoelectrical potentials superimposed on volitional ones. The instantaneous frequency of superim posed M-waves and mean power frequencies of volitional electromyography (EMG) declined during sustained contraction, indicating that fatigue progressed. We divided fatigue into 3 phases, with 20 frames in each fatigue phase, corresponding to one-third of the total sample. The instantaneous frequency of superimposed M-waves and mean power frequencies of volitional EMG were correlated during early intensive isometric voluntary contractions and became increasingly uncorrelated as contraction proceeded. The coefficient between the mean power frequency and instantaneous frequency correlation was also greater at the first peak than at the second peak of the superimposed M-wave, indicating that the motor unit action potential was distorted. Distortion in the motor unit action potential shape depends on elongation of the depolarization zone of muscle fiber, because the superimposed M-wave is a peripheral indicator elicited by electrical stimulation. These results suggest that muscle fatigue develops based on the reduction of the conduction velocity of muscle fiber and on the elongation of the depolarization zone of muscle fiber.     

Stage analysis of the reaction process using brain-evoked potentials and reaction time

Summary Motor processes partly determine reaction time (RT) in both choice reaction time and in binary classification tasks. These latter tasks are popular in cognitive psychology because the experimenter believes that he has kept the motor component simple and constant and therefore can attribute changes in RT to perceptual or cognitive processes. In this paper we used the P3 component of the event-related potential (ERP) as a time marker indicating the duration of perceptual and cognitive processes. The latency of this component is believed to reflect stimulus evaluation time independent of response selection and organization time.Two types of tasks were used: a choice-reaction time task and a binary classification task. Signal similarity and S-R compatibility additively affected RT, but only signal similarity affected P3 latency. The number of items in the positive set and response type affected both P3 latency and RT. Relative response frequency changed the bias in the cognitive evaluation of the stimulus, reflected in the latency of the P3 component, and affected RT only if the subjects preset their motor system (indexed by the late CNV). A model was presented which proposes that motor processes may partially overlap with the perceptual and cognitive evaluation of the stimulus. Both ERPs and RT are necessary tools in the study of the relative timing of these processes.     

Achilles Tendon Reflexes and Surface EMG Activity during Anticipation of a Significant Event and Preparation for a Voluntary Movement

Achilles tendon reflexes were evoked bilaterally during and shortly after an interstimulus-interval (ISI) of 4 s and expressed as percentages of an averaged control reflex. Surface EMG of the soleus muscles was recorded continuously during the ISI, and expressed as percentages of a control EMG level. Three types of tasks were introduced, according to a between subjects design. Condition I consisted of a guessing task, involving anticipation of the second stimulus (S2) and not requiring a motor response. Conditions II and III were a warned choice and simple RT task respectively, the motor response to S2 being a plantar flexion of either the left or right foot in Condition II, and a plantar flexion of the right foot in Condition III. The results can be stated as follows: 1. Anticipation of a stimulus is not sufficient for a reflex increase to occur during an ISI. Preparation for a movement seems to be a necessary condition.

2. The reflex increase during preparation is rather independent of the amount of selectivity in the preparatory process; simple and choice RT tasks yield similar results, although the mean RTs do differ.

3. A difference between the involved and non-involved legs in the simple RT task is not found in the present experiment, as opposed to other studies. The particular instruction given to the subjects could be of importance in producing this difference.

4. Reflex changes cannot simply be accounted for by changes in background EMG of the agonist, as the EMG time course shows no changes over time in either condition.

     

Stimulus-response compatibility and response preparation: effects on motor component of information processing for upper and lower limb responses

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.     

Effects of physical fatigue and cognitive challenges on the potential for low back injury

There is no question that the motor control system will adapt under fatiguing conditions; however, there is documented evidence showing that when fatigued or challenged, the motor control system will, on occasion, perform inappropriate muscle sequencing, increasing the risk of injury, or directly causing injury. Knowing that inappropriate muscle activations can lead to injury, the purpose of this study was to investigate motor patterns during cognitive and physical challenges. Rather than ensure change with severe challenges, milder challenges were purposefully chosen. Eight male subjects performed a low external load task performed near end ROM while in an unchallenged state, and while in three challenged states: passive tissue creep, muscle fatigue and cognitive distraction. Data were collected using EMG of the trunk muscles and angular displacement of the lumbar spine. Comparison of motor control patterns between the unchallenged state and each of the three challenged conditions showed no systematic differences. However, several random anomalies were observed. A case study of a single subject was chosen to show inappropriate motor control during one trial under the cognitive distraction conditions. The response of the motor control system is very individualized and does on occasion produce inappropriate motor patterns. This supports the notion that injury may also occur as the result of random motor control errors as well as predictable, systematic changes.