Visual load and variability of muscle activation: Effects on reactive driving of older adults

BackgroundThe functional significance of the increase in motor output variability with increased visual information processing in older adults remains unclear. Here, we test the hypothesis that increased visual information processing increases muscle activation variability in older adults and impairs their ability to react as fast and as precisely as young adults during a simulated reactive driving task.MethodsFourteen young and sixteen older adults performed a reactive driving simulation task that required responding to unexpected brake lights of the car ahead during a simple reaction time task (low visual information processing condition) and a choice reaction time task with “no go” trials condition (high visual information processing condition). We quantified the following: 1) reactive driving performance – combination of premotor response time, motor response time, and brake force error; 2) motor output variability – brake impulse variability; 3) muscle activation variability – variability in the tibialis anterior (TA) muscle activity.ResultsThe increase in information processing exacerbated the impaired reactive driving performance in older adults. The best predictor of this impairment was the increase in brake force error. The impaired reactive driving performance was related to brake impulse variability and variability in the TA activity.ConclusionsThis study provides novel evidence that increased information processing increases muscle activation variability in older adults with detrimental consequences to their ability to perform a simulated reactive driving task.     

The influence of advance information on the response complexity effect in manual aiming movements

The relation between reaction time and the number of elements in a response has been shown to depend on whether simple or choice RT paradigms are employed. The purpose of the present study was to investigate whether advance information about the number of elements is the critical factor mediating the influence between reaction time and response elements. Participants performed aiming movements that varied in terms of the number of elements and movement amplitude. Prior to the stimulus, advance information was given about the number of elements and movement amplitude, movement amplitude only, number of elements only, or no information about the response. Reaction time and movement time to the first target increased as a function of number of elements only when the full response or the number of elements was specified in advance of the stimulus. The implication of these results for current models of motor programming and sequential control of aiming movements are discussed.     

An electrophysiological model of human visual reaction time

Human visual reaction times were fractionated into component latencies measuring visual reception time, opto-motor integration time, central motor outflow time, and peripheral motor time on the basis of evoked cortical activity recorded from the intact scalp and the occurrence of the response electromyogram. Normative data are presented for a right-foot dorsiflexion task studied on 18 male subjects, together with an analysis of inter- and intra-subject variability in response timing. Faster reactors were found to display briefer opto-motor integration times and motor times, while an individual's faster responses were characterized by shorter motor outflow times and motor time. These results are interpreted in terms of varying physiological mechanisms.     

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.     

Relationships between movement initiation times and movement-related cortical potentials in Parkinson's disease

Movement-related cortical potentials recorded from the scalp reveal increasing cortical activity occurring prior to voluntary movement. Studies of set-related cortical activity recorded from single neurones within premotor and supplementary motor areas in monkeys suggest that such premovement activity may act to prime activity of appropriate motor units in readiness to move, thereby facilitating the movement response. Such a role of early stage premovement activity in movement-related cortical potentials was investigated by examining the relationship between premovement cortical activity and movement initiation or reaction times. Parkinson's disease and control subjects performed a simple button-pressing reaction time task and individual movement-related potentials were averaged for responses with short compared with long reaction times. For Parkinson's disease subjects but not for the control subjects, early stage premovement cortical activity was significantly increased in amplitude for faster reaction times, indicating that there is indeed a relationship between premovement cortical activity amplitude and movement initiation or reaction times. In support of studies of set-related cortical activity in monkeys, it is therefore suggested that early stage premovement activity reflects the priming of appropriate motor units of primary motor cortex, thereby reducing movement initiation or reaction times.PsycINFO classification: 2330; 2520; 2530     

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.     

Response force in RT tasks: Isolating effects of stimulus probability and response probability

Mattes, UIrich, and Miller (1997) found that as response probability decreases in a simple reaction time (RT) task, participants produce more forceful responses as well as longer RTs, suggesting a direct influence of preparatory processes on the motor system. In this previous study, however, response probability was confounded with stimulus probability, leaving open the possibility that response force was sensitive to stimulus- rather than response-related preparation. The present study was conducted to unravel the effects of stimulus and response probability. Experiment 1 manipulated stimulus probability and revealed that responses to a more probable stimulus are less forceful than responses to a less probable stimulus even when both stimuli require the same response. Experiment 2 demonstrated that this stimulus probability effect does not depend on the overall level of response probability. Experiment 3 showed an analogous effect for response probability when stimulus probability is kept constant. The complete pattern of results suggests that both stimulus probability and response probability affect the forcefulness of a response. It is argued that response probability exerts adirect influence on the motor system, whereas stimulus probability influences the motor system indirectly via premotoric adjustments.     

Response timing variability: coherence of kinematic and EMG parameters

A detailed kinematic and electromyographic (EMG) analysis of single degree of freedom timing responses is reported to (a) determine the coherence of kinematic and EMG variability to the reduced timing error variability exhibited with amplitude increments within a given criterion movement time and (b) understand the temporal organization of various movement parameters in simple responses. The data reveal that the variability of kinematic (time to peak acceleration, duration of acceleration phase, time to peak deceleration) and EMG (duration of agonist burst, duration of antagonist burst, time to antagonist burst) timing parameters decreased with increments of average velocity in a manner consistent with the variable timing error. In addition, the coefficient of variation for peak acceleration, peak deceleration, and integrated EMG of the agonist burst followed the same trend. Increasing average movement velocity also led to decreases in premotor and motor reaction times. Overall, the findings suggest a strong coherence between the variability of response outcome, kinematic, and EMG parameters.     

Response Timing Variability

A detailed kinematic and electromyographic (EMG) analysis of single degree of freedom timing responses is reported to (a) determine the coherence of kinematic and EMG variability to the reduced timing error variability exhibited with amplitude increments within a given criterion movement time and (b) understand the temporal organization of various movement parameters in simple responses. The data reveal that the variability of kinematic (time to peak acceleration, duration of acceleration phase, time to peak deceleration) and EMG (duration of agonist burst, duration of antagonist burst, time to antagonist burst) timing parameters decreased with increments of average velocity in a manner consistent with the variable timing error. In addition, the coefficient of variation for peak acceleration, peak deceleration, and integrated EMG of the agonist burst followed the same trend. Increasing average movement velocity also led to decreases in premotor and motor reaction times. Overall, the findings suggest a strong coherence between the variability of response outcome, kinematic, and EMG parameters.     

Increased Intrasubject Variability in Boys with ADHD Across Tests of Motor and Cognitive Control

Increased intrasubject variability (ISV), or short-term, within-person fluctuations in behavioral performance is consistently found in Attention-Deficit/Hyperactivity Disorder (ADHD). ADHD is also associated with impairments in motor control, particularly in boys. The results of the few studies that have examined variability in self-generated motor output in children with ADHD have been inconsistent. The current study examined variability in motor control during a finger sequencing task among boys with and without ADHD as well as the relationship between intrasubject variability during motor and cognitive control tasks. Changes in performance over the course of the task and associations with ADHD symptom domains were also examined to elucidate the nature of impaired motor control in children with ADHD. Fifty-one boys (ages 8 to 12 years) participated in the study, including 28 boys with ADHD and 23 typically developing (TD) boys. Participants completed a finger sequencing task and a Go/No-Go task providing multiple measures of response speed and variability. Boys with ADHD were slower and more variable in both intertap interval on the finger sequencing task and reaction time on the Go/No-Go task, with measures of speed and variability correlated across the two tasks. For the entire cohort, the only unique predictor of parent ratings of hyperactive-impulsive symptoms was variability in intertap interval during finger sequencing, whereas inattentive symptoms were only predicted by reaction time variability on the Go/No-Go task. These findings suggest that inefficient motor control is implicated in the pathophysiology of ADHD, particularly in regards to developmentally inappropriate levels of hyperactivity and impulsivity.     

Methods in the study of motor programming: is it just a matter of simple vs. choice reaction time? A comment on Klapp et al. (1979)

A recent article (Klapp, Abbott, Coffman, Greim, Snider, and Young, 1979) has concluded that central time demands of motor programming can only be determined by choice reaction time methodology. A critique of the theoretical position and results of this study is made showing that this conclusion is unwarranted. We go on to suggest that the simple vs. choice reaction time controversy might only be clouding a more basic issue in motor programming research; viz., identification of relevant internal response variables. Finally, a case is made for the notion that the choice reaction time paradigm may produce response competition (interference) effects and as a result confound measures presumed to reflect only the processes involved in the organization of movement.     

Use of partial stimulus information in response processing

We examined the reaction time benefit that is obtained when salient features of the stimulus set and response set correspond. Components of the event-related brain potentials were used to measure the timing of stimulus-related and response-related processes in order to determine the locus of this effect. Of particular importance was the development of a new index of selective response preparation, the corrected motor asymmetry (CMA). We found no evidence for the use of preliminary, partial stimulus information in response preparation. These results suggest that the benefit is located primarily in response selection processes and probably reflects a more efficient algorithm for stimulus-response translation. Also, we found trial-to-trial variability in the duration of response selection to be the major determinant of variability in reaction time, whereas the durations of subsequent response-related processes were relatively invariant. Implications of these results for discrete and continuous models of choice reaction performance are discussed.     

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.     

Equivalency of reaction times for simple and primed tasks

Both simple and choice reaction-time tasks have been used to examine the processes involved in response preparation. With a response priming task, complete information prior to the presentation of the imperative stimulus is given as to which response among several will be required. It is assumed that with the priming procedure, the advanced information allows for the complete preparation of the response to be made prior to the presentation of the imperative stimulus [Klapp, S. T. (1996). Reaction time analysis of central motor control. In H. N. Zelaznik (Ed.), Advances in motor learning and control (pp. 13-36). Champaign, IL: Human Kinetics]. This study used two experiments to test the underlying assumption that the processes occurring within the reaction time interval are equivalent for simple and primed tasks, and to determine if the validity of the prime influences performance. In both experiments, participants completed three reaction-time tasks: simple, primed (100%), and choice. The second experiment added a fourth task in which the prime was valid only 80% of the time. In both experiments, the reaction times were significantly slower for the choice task than for either the simple or 100%-primed tasks. Most important, the simple and primed (100%) reaction times were not significantly different. For the second experiment, the reaction times were not significantly different for the choice and 80%-valid prime tasks. The results of these experiments demonstrate that equivalent response preparation processes occur for simple and primed tasks, but that the validity of the prime does influence the response preparation processes for the primed task. Thus, equivalency is not achieved when invalid primes are used.     

Relationship between reaction time variability and motor skill development in ADHD

Slower and more variable reaction times to computerized tasks have been documented in children diagnosed with attention deficit/hyperactivity disorder (ADHD). Recent research supports a role for attentional lapses in generating abnormally variable and slow responses. However, given the association between ADHD and impairments in motor control, we hypothesized that slower or more variable reaction times might also correlate with motor development. The aim of this case-control study was to explore the relationship between motor function, reaction speed and variability, and ADHD. After comprehensive educational and clinical assessments, motor skill development was evaluated in 35 children ages 9 to 14 (19 with ADHD) using the Physical and Neurological Examination for Subtle Signs (PANESS) test battery. Finger-sequencing speed and variability were quantified with goniometers. Reaction times were measured with 20 trials each of computerized simple and choice (binary) tasks. Compared to healthy controls, children with ADHD had slower and more variable reaction times, and these findings correlated with impaired motor development (PANESS) and slow and variable finger sequencing (goniometers). Further studies of motor development in ADHD may identify factors influencing speed and variability of reaction times.     

Relationship between reaction time variability and motor skill development in ADHD

Slower and more variable reaction times to computerized tasks have been documented in children diagnosed with attention deficit/hyperactivity disorder (ADHD). Recent research supports a role for attentional lapses in generating abnormally variable and slow responses. However, given the association between ADHD and impairments in motor control, we hypothesized that slower or more variable reaction times might also correlate with motor development. The aim of this case-control study was to explore the relationship between motor function, reaction speed and variability, and ADHD. After comprehensive educational and clinical assessments, motor skill development was evaluated in 35 children ages 9 to 14 (19 with ADHD) using the Physical and Neurological Examination for Subtle Signs (PANESS) test battery. Finger-sequencing speed and variability were quantified with goniometers. Reaction times were measured with 20 trials each of computerized simple and choice (binary) tasks. Compared to healthy controls, children with ADHD had slower and more variable reaction times, and these findings correlated with impaired motor development (PANESS) and slow and variable finger sequencing (goniometers). Further studies of motor development in ADHD may identify factors influencing speed and variability of reaction times.     

Behavioral definition of minimal reaction time in monkeys

Two monkeys (Macaca mulatta) were trained to press a key after onset of a tone and to release it after a 1-sec fixed foreperiod terminated by a light. The effects of imposing temporal contingencies on key release reaction times were determined by reinforcing only those releases whose latencies from the light fell within a “payoff band”, two time limits 50 msec apart located at some delay following the light. Over several days this delay was first gradually decreased, shortening the interval between light and payoff band, and then gradually increased again. For each delay, the median reaction time and a measure of variability were obtained from the latency distribution. For both animals, median latency could be decreased to 180 msec with the variability remaining small. Moving the payoff band still closer to the light resulted in further decrease in median latency but an abrupt increase in variability. This is in agreement with a model for simple reaction time derived from human research which suggests that this increased variability results from the inclusion of high-variability foreperiod time estimations in the latency distribution. These results indicate that interpretation of monkey response latencies as “minimal reaction times” requires examination of temporal reinforcement contingencies and variability of latencies.     

Fractioned reaction time as a function of response force

The relationship between fractionated reaction time components and response force was studied in a simple reaction time task. Subjects squeezed a force transducer between the right thumb and index finger. Three conditions with 5, 25, and 50% of the maximum voluntary isometric force were investigated in a counterbalanced order. The results showed that premotor reaction time was negatively related to peak force amplitude, while motor reaction time remained constant across force conditions. An interpretation of the effect on premotor reaction time in terms of a shift in the speed-accuracy trade-off function was refuted. Although the data were consistent with a two-stage programming model, it was concluded that differences in motor nerve fiber conduction velocity as a function of response force could explain the results obtained.     

Manual reaction time to linguistic stimuli in child stutterers and nonstutterers

Ten stuttering and ten nonstuttering children, ages 4–8 yr, served as subjects for a motor reaction task to simple and complex linguistic stimuli. The subjects reacted by pressing one of four panels on a touch-sensitive board that depicted the appropriate semantic relationship in response to 30 simple and complex linguistic stimuli. There was a significant increase in the reaction time of both groups with increasing linguistic complexity. No significant differences were found in the reaction time between the two groups, nor in the interaction between group and complexity. Implications regarding linguistic processing are discussed, and an “overload” hypothesis of stuttering is dispelled. It is concluded that stutterers and nonstutterers in this study did not differ in their reaction time nor in their processing time of linguistic material.     

An event-related potential analysis of extraversion and individual differences in cognitive processing speed and response execution

Individual differences in cognitive processing speed and response execution were examined in relation to extraversion. Event-related potentials (ERPs) were recorded concurrently with reaction time and movement time (MT) measures as participants (N = 67) performed simple reaction time and stimulus-response compatibility tasks. Slower processing speed for extraverts, as indicated by longer latency of a late positive ERP wave, P3, was only evident in conditions in which stimulus information was in conflict with response selection demands. As previously reported, the salient effect in all conditions of both tasks was faster MT for extraverts, an effect that is indicative of differences in fundamental motor processes. On the simple reaction time task, amplitudes of the N1 component, an early negative ERP wave, were smaller for extraverts than for introverts in response to auditory tones, an effect that affirms the enhanced sensory reactivity of introverts to punctate physical stimuli.