Reaction time and response dynamics

Young male motorcycle rider perception response times to abrupt- and gradual-onset hazards

Response time (RT) measures in crash reconstruction are inherently constrained by the need to define a start point (onset). In straight-forward situations where the hazard appears abruptly from behind an obstruction (abrupt onset), hazard onset is typically defined as when the hazard is first visible to the motorist. In contrast, in scenarios where there is no clearly defined point of entry (gradual onset), and the potential hazard gradually transitions to an immediate hazard, the onset point is more ambiguous. In this study, a reasonable hazard onset was proposed for measuring RTs of motorcycle riders to gradual-onset hazards, following which the RTs to abrupt- and gradual-onset hazards were determined and compared. A study on motorcycle rider RTs was conducted in Singapore in which a sample of young male adults (licensed riders with more than one year's effective riding experience, and unlicensed subjects) were equipped with eye tracking glasses and were presented with two pairs of abrupt-/ gradual-onset hazard scenarios on a simple motorcycle simulator. Their RTs were recorded. Initial deviation from the straight path (start of turning manoeuvre) of the intruding hazard vehicle was determined to be a more appropriate onset (start point when measuring RTs) for gradual-onset hazards when compared with referencing the onset against travel lane incursions. Participants generally took longer to respond to gradual-onset hazards than abrupt-onset hazards. Unlicensed subjects tended to underperform relative to licensed riders. The findings from this study contribute to the literature in the relatively novel field of motorcycle RTs and should be of interest to crash reconstructionists as well road safety professionals in designing road operations.

Effects of Mental Effort on Premotor Muscle Activity and Maximal Grip Force

The present study sought to evaluate how mental effort modulates premotor activity within forearm muscles in the context of an isometric grasping task. Muscle activity of the flexor digitorum superficialis (FDS) and extensor digitorum communis (EDC) was recorded during the application of maximum grip forces in nineteen healthy adult subjects. Each subject was examined under two experimental conditions: 1) spontaneous initiation of grasp (SI) and 2) focused concentration preceding the initiation of grasp (CA). Two novel parameters, the mean premotor duration (MPD) and the mean premotor power (MPP) were used to distinguish patterns of muscle activity. Here we tested the hypothesis was maximal grip strength is primed by muscle activity during the premotor phase. Our results demonstrate that MPD for each muscle group was significantly longer in the CA condition than for the SI condition (BF₁₀ = 491497) and that MPP was significantly greater in EDC than in FDS (BF₁₀ = 4305). Furthermore, both the MPD and MPP of the EDC were significantly correlated with maximum grip force. These results suggest that the increase of premotor activity consequent to the mental effort (focused concentration) may support internal biomechanical and physiological mechanisms which serve to enhance patterns of neuromuscular synergies.

Real-time slacking as a default mode of grip force control: implications for force minimization and personal grip force variation

During trial-to-trial movement adaptation, the motor system systematically reduces extraneous muscle forces when kinematic errors experienced on previous movements are small, a phenomenon termed "slacking." There is also growing evidence that the motor system slacks continuously (i.e., in real-time) during arm movement or grip force control, but the initiation of this slacking is not well-characterized, obfuscating its physiological cause. Here, we addressed this issue by asking participants ( n = 32) to track discrete force targets presented visually using isometric grip force, then applying a brief, subtle error-clamp to that visual feedback on random trials. Participants reduced their force in an exponential fashion, on these error-clamp trials, except when the target force was <10% maximum voluntary contraction (MVC). This force drift began <250 ms after the onset of the error-clamp, consistent with slacking being an ongoing process unmasked immediately after the motor system finished reacting to the last veridical feedback. Above 10% MVC, the slacking rate increased linearly with grip force magnitude. Grip force variation was approximately 50-100% higher with veridical feedback, largely due to heightened signal power at ~1 Hz, the band of visuomotor feedback control. Finally, the slacking rate measured for each participant during error-clamp trials correlated with their force variation during control trials. That is, participants who slacked more had greater force variation. These results suggest that real-time slacking continuously reduces grip force until visual error prompts correction. Whereas such slacking is suited for force minimization, it may also account for ~30% of the variability in personal grip force variation. NEW & NOTEWORTHY We provide evidence that a form of slacking continuously conditions real-time grip force production. This slacking is well-suited to promote efficiency but is expected to increase force variation by triggering additional feedback corrections. Moreover, we show that the rate at which a person slacks is substantially correlated with the variation of their grip force. In combination, at the neurophysiological level, our results suggest slacking is caused by one or more relatively smooth neural adaptations.

Programming of Time-to-Peak Force for Brief Isometric Force Pulses: Effects on Reaction Time

According to the parallel force unit model (PFUM) the programming of an isometric force pulse requires the specification of the number of force units and force unit duration. The programming of a force pulse with minimal time-to-peak force is an exception, however, as force unit duration is limited by the minimal possible value, which should be easier to adjust than larger force unit durations. Therefore, the duration of the programming process should be shorter for these force pulses and hence should result in shorter reaction time (RT). Four experiments assessed this prediction using a response precueing procedure. In each experiment the participants produced isometric flexions with their left or right index finger, and time-to-peak force was manipulated within a block. The results are consistent with the predictions of PFUM. The results, however, are at variance with alternative accounts which assume that RT depends primarily on response duration or rate of force production.

Programming strategies for rapid aiming movements under simple and choice reaction time conditions

Increases in reaction time (RT) as a function of response complexity have been shown to differ between simple and choice RT tasks. Of interest in the present study was whether the influence of response complexity on RT depends on the extent to which movements are programmed in advance of movement initiation versus during execution (i.e., online). The task consisted of manual aiming movements to one or two targets (one- vs. two-element responses) under simple and choice RT conditions. The probe RT technique was employed to assess attention demands during RT and movement execution. Simple RT was greater for the two- than for the single-target responses but choice RT was not influenced by the number of elements. In both RT tasks, reaction times to the probe increased as a function of number of elements when the probe occurred during movement execution. The presence of the probe also caused an increase in aiming errors in the simple but not choice RT task. These findings indicated that online programming was occurring in both RT tasks. In the simple RT task, increased executive control mediated the integration between response elements through the utilization of visual feedback to facilitate the implementation of the second element.

Electromechanical delay: An experimental artifact

The time delay between the onset of muscle activation and the onset of force or motion is commonly referred to as electromechanical delay, motor time, or motor execution time. This time has been used in the study of reaction time, of physiological properties of muscle, and of population differences. In this study, we show that electromechanical delay is comprised of two components. The first is transport time (t(t)) which is very brief (perhaps 10 ms). The second is the time to generate detectable changes in force (t(f)). The absolute duration of electromechanical delay is usually dominated by the second component which is influenced by four separate factors that are related in the following way: [Formula: see text] That is, t(f) is a function (g) of the product of two ratios. One is between the threshold T of the measuring device and the rate R at which muscle force rises. The other is the ratio of the mechanical impedances of the measuring device (Z(d)) and the muscle (Z(m)). We conclude that the measured absolute value of electromechanical delay has no physiological or psychological meaning and that task and performance induced changes need great care in their interpretation.

An inexpensive and accurate method of measuring the force of responses in reaction time research

Together with reaction time (RT), the force with which people respond to stimuli can provide important clues about cognitive and affective processes. We discuss some of the issues surrounding the accurate measurement and interpretation of response force, and present a response key by which response force can be measured regularly and unobtrusively in RT research. The advantage of the response key described is that it operates like a standard response key of the type used regularly in classic RT experiments. The construction of the response key is described in detail and its potential assessed by way of an experiment examining response force in a simple reaction task to visual stimuli of increasing brightness and size.

Effects of response sequence length on motor programming: a chronometric analysis

The present experiment studied choice response context effects on the programming of response sequences using behavioural and electrophysiological methods. Participants were asked to produce responses differing in sequence length (1-key vs. 3-key responses) with either their left or right hand in a choice reaction time (RT) task. The choice response context was manipulated by a blocked or mixed execution of 1-key and 3-key responses. A sequence length effect on RT was observed in the blocked but not in the mixed condition. The time course of the lateralized readiness potential indicates a motoric locus of the sequence length effect, suggesting that the response hand is activated before the entire motor program is established.

The independence of response structure and element production in timing sequences

In three experiments, participants were asked to produce a prescribed temporal sequence of key presses. The number of elements in a key press sequence, the movement time of the elements, and uniformity of the timing elements comprising the sequence were manipulated. If the processing of the sequence structure was independent of the processing of elements comprising the sequence, increasing the number of the elements in the sequence should affect the production of the sequence but not the proficiency with which the individual elements are, produced. Increasing the movement time of the elements, however, should affect the production of the elements but have little, if any, effect on the integrity of the sequence. The findings indicated that increasing the number of elements negatively affected sequence production when the elements were nonuniform but had little or no effect when elements were uniform. Alternatively, element production was affected by movement time but not number of elements. The results of these experiments appear to confirm the independence of sequence and element production. However, Experiment 3, in which the uniformity of the elements was directly contrasted, found strong evidence for coarticulatory influences in the learning processes, whereby the longer and shorter than average elements in the sequence negatively affected the sequence integrity and the production of the individual elements. When faced with a nonuniformn timing pattern, participants appear to elongate or shrink individual elements of a uniform timing pattern to fit the desired sequence requirements. The result is that the longer or shorter than average elements require more practice to produce correctly, tend to regress across retention intervals, and are generally less stable than the elements nearer the average.

The impact of anticipated action effects on action planning

Three experiments with a total of 72 participants investigated the assumption that motor actions are planned in terms of their sensorial effects. Participants had to prepare a certain action A that consistently led to a sensorial effect (a tone of certain pitch). Instead of (in Experiment 1) or before (in Experiments 2 and 3) the execution of the prepared action, another response B had to be carried out, which either resulted in the same or in a different auditory effect (a tone of same or different pitch). It was found that a to-be-executed response B was in general initiated more quickly when it resulted in the same effect as a concurrently prepared response A. The results are considered as evidence for the basic notion that the preparation and initiation even of very simple actions is mediated by an anticipation of their reafferences.

A psychophysiological analysis of inhibitory motor control in the stop-signal paradigm

We examined two potential inhibitory mechanisms for stopping a motor response. Participants performed a standard visual two-choice task in which visual stop signals and no-go signals were presented on a small proportion of the trials. Psychophysiological measures were taken during task performance to examine the time course of response activation and inhibition. The results were consistent with a horse race model previously proposed to account for data obtained using a stop-signal paradigm. The pattern of psychophysiological responses was similar on stop-signal and no-go trials suggesting that the same mechanism may initiate inhibitory control in both situations. We found a distinct frontal brain wave suggesting that inhibitory motor control is instigated from the frontal cortex. The results are best explained in terms of a single, centrally located inhibition mechanism. Results are discussed in terms of current neurophysiological knowledge.

Force and timing variability in rhythmic unimanual tapping

In 3 experiments the interdependencies between timing and force production in unimanual paced and self-paced rhythmic tapping tasks were examined as participants (N = 6 in each experiment) tapped (a) to 1 of 3 target periods (333 ms, 500 ms, and 1,000 ms), while they simultaneously produced a constant peak force (PF) over a 50-s trial; (b) to produce 1 of 3 target forces (5, 10, and 15 N) at their preferred frequency, while keeping their rhythm as invariant as possible; and (c) to all combinations of target force and period. The results showed that (a) magnitudes of force and period were largely independent; (b) variability in timing increased proportionally with tapping period, and the variability in force increased with peak force; (c) force variability decreased at faster tapping rates; and (d) timing variability decreased with increasing force levels. (e) Analysis of tap-to-tap variability revealed adjustments over sequences of taps and an acceleration in the tapping rate in unpaced conditions. The interdependencies of force and time are discussed with respect to the challenges they provide for an oscillator-based account.

Fractionated reaction time as a function of magnitude of force in simple and choice conditions

The present study examined whether varying magnitude of force required to perform an isometric response influences fractionated reaction time in simple and choice conditions and whether reaction time and premotor time to initiate the response are shorter when force is selected freely by the subject than when it is selected by the experimenter. 20 subjects were required to react and produce a designated peak force as quickly and accurately as possible by squeezing a handle after a reaction signal. Four different magnitudes of force were 30, 50, and 70% of the maximum grip strength of the subjects and subject-selected magnitude of force. Reaction time and premotor time did not change across the range of forces examined in both simple and choice reaction-time conditions regardless of whether a desired force was selected by the experimenter or by the subject. These findings suggest that programming an isometric response may require a constant amount of time.

Gait initiation in Parkinson's disease

We studied the kinematic patterns of gait initiation in 31 patients with Parkinson's disease and in 20 age- and sex-matched normals by using an optoelectronic tracking system (ELITE). Position markers were attached to the skin overlying the ankle, knee, hip, elbow, shoulder, and zygomatic bone. Subjects were instructed to start walking immediately after an acoustic go signal. Gait initiation was defined as the phase between standing motionless and steady-state locomotion. This phase was subdivided into a movement preparation period (the time between go signal and movement onset) and a movement execution period (the time between movement onset and the end of the first stride). Onset and duration of ankle, knee, hip, trunk, and arm motion within the first stride were analyzed. Movement preparation time was significantly increased in Parkinson's disease (p = 0.01), whereas movement execution times were similar in both groups (p = 0.23). Initiation of ankle, knee, hip, arm, and trunk movements was delayed in patients as compared with healthy subjects, but the relative timing and the sequence of submovements was comparable in both groups, indicating that the overall pattern of submovements was preserved in the patients. Our data suggest that gait initiation deficits in Parkinson's disease cannot be explained by a disordered sequence of limb and trunk submovements. More likely, gait initiation problems originate from the basal ganglia's internal cueing deficit for movement sequences, delaying onset and slowing the execution of all subcomponents.

Does immediate arousal enhance response force in simple reaction time?

Three experiments assessed the hypothesis that immediate arousal enhances response force in speeded reaction-time tasks. Immediate arousal was manipulated via the physical characteristics of a warning signal that closely preceded the imperative response signal. The first experiment revealed that responses were more forceful and faster for a loud than for a soft warning signal. The second experiment manipulated the duration of an auditory warning signal; more forceful but slower responses were obtained for longer durations of the warning signal. The third experiment employed a visual warning signal, and its intensity was either rather weak or moderately bright; more forceful responses and slightly faster responses were observed for the brighter warning signal. Although the results of Experiment 1 and 2 may agree with an arousal account, the findings of Experiment 3 argue against such an account. A stimulus-response compatibility hypothesis is suggested as one possible alternative account.

Planning for hand shape and arm transport when reaching for objects

Two early components of object manipulation are shaping the hand appropriately for functional interaction and transporting the arm with appropriate force and spatial precision to the target object. Three experiments addressed whether people plan these two components before the onset of reaching and if so, how the plans are coordinated. Subjects reached for and contacted a series of objects with one of four hand configurations: pinch, poke, palm, and clench. The required configuration was signaled by the object's color; in some conditions its structure provided a redundant cue. The time from object exposure to arm liftoff (reaction time: RT) and the time from liftoff to contact (movement time: MT) were recorded. In Experiment 1, a compatible stimulus-to-hand-shape mapping substantially facilitated RT but not MT, suggesting that the appropriate hand shape was planned prior to reaching. Experiment 2 showed that contact precision, as defined by the stability of the object's support plane, affected MT; a smaller RT effect also suggested some pre-movement planning of arm transport to accommodate precision demands. Experiment 3 combined compatibility and precision manipulations in a single task to test a model which proposes that planning for hand-shape and arm transport occur in parallel, with the onset of reaching deferred until the slower planning process is completed.

Tremor as a factor in prolonged reaction times of parkinsonian patients

Prolonged reaction times and tremor are symptoms of Parkinson's disease (PD). Recently, we showed the existence of a systematic phase relationship between tremor-at-rest and the onset of voluntary motor responses in PD patients. In the present study we investigated whether this phase relationship contributes to the prolongation of reaction time in PD. Eight PD patients with prominent tremor-at-rest and five age-matched controls performed rapid stimulus-evoked index finger abductions under isometric conditions. Force and surface electromyogram (EMG) signals from first dorsal interosseus muscle were recorded and analyzed off-line by means of automatic routines. Reaction times of PD patients exhibited a significant dependence of mean values and variability on the current tremor phase at the onset of the voluntary motor response. Responses with an onset of contraction during the beginning of an EMG tremor burst were substantially delayed (on average 50 ms) and showed more variability in comparison to responses initiated at later times in the tremor cycle. This effect can be modeled by a simple gating process splitting the tremor cycle into two different system states that supports and inhibits the initiation of voluntary motor responses, respectively. We conclude that attraction of voluntary motor initiation to the tremor oscillator clearly contributes to prolongation of reaction time in PD.

Effects of Object Texture on Precontact Movement Time in Human Prehension

Using kinematic data in a precision-grip reaching task, Weir, MacKenzie, Marteniuk, and Cargoe (1991) concluded that prior to contact with an object, its texture does not affect the course of grasping. The present study used their task of reaching for and lifting a slippery-, normal- (polished metal), or rough-surfaced dowel. This occurred under the original, blocked condition, in which textures were held constant within a series of trials, and under a new, randomized condition, in which textures varied randomly from trial to trial. Performance was also examined over more extended periods of practice. Reaction time and precontact movement time were directly measured. In contrast to the results of Weir et al., 1991, reaching for the slippery dowel resulted in slower movement time. This effect was found both early and late in practice for the randomized condition; it was found only in late practice for the blocked condition. These effects can be attributed to the greater geometric and dynamic precision required for lifting a slippery object.

Combined Effects of Movement Velocity and Duration on Programming Time: Spijkers (1989) Revisited

The goal of the present study was to determine the combined effects of movement velocity and duration on motor programming. Subjects were submitted to a two-choice reaction time task that could be completed by aiming movements differing in the mean velocity at which they were to be produced as well as by their movement time. The results of the present study indicate that, in each pair of responses used, the responses having the higher mean velocity were initiated faster that those having the lower mean velocity. Contrary to Spijkers' (1989) study, the different movement time pairings did not modify the effect of movement velocity on response programming time. Moreover, the same pattern of results was observed whether or not the subjects were permitted to visually guide their ongoing movement. Thus, Spijkers' proposition, that the type of control one may use to guide an aiming movement needs to be determined before movement initiation can take place, was not confirmed.

Determining Movement Onsets from Temporal Series

With the advent of recent measurement techniques, kinematic and kinetic measures commonly are used to describe events over time. Often, the central and peripheral nature of the control processes involved are derived from these temporal series. For example, movement onset often arbitrarily defines the end of the central and the beginning of the peripheral processes. Because of its critical temporal location, we examined whether response dynamics (average movement velocity) affects the determination of movement onset. Interactive graphics and numerical methods of determining movement onsets from temporal series were evaluated on various kinematic signals. Variations in the initial rate of change in a given signal significantly affected the determination of movement onset. Consequently, measurements of component latency must be regarded with caution. A cursory description of related problems elucidated in previous research is discussed, and procedures that can minimize these artifacts are suggested.

Effects of force output and preparatory period on fractionated reaction time

The effects of force output and its preparatory period on fractionated reaction time were investigated. Eight subjects responded with an isometric elbow flexion to light stimuli under three experimental conditions, adjusting force output to match two target forces (10% or 40% of maximal isometric voluntary elbow flexion strength) displayed on an oscilloscope. Analysis indicates that the relationship between premotor time and force output is affected by preparatory states in the central nervous system, and the preparatory time necessary for exertion of a specific force varies with the magnitude of exerted force.

Motor Programming as a Function of Constraints on Movement Initiation

Three experiments are reported that test the hypothesis that under certain conditions programming time is a function of the directional accuracy demand of a response, directional accuracy being quantified by the minimal angle subtended at the point of movement initiation by the circular targets within the response. Subjects in three simple reaction time experiments were required to tap a single target or a series of circular targets as rapidly as possible with a hand-held stylus. Experiments 1 and 3 showed that the subtended angle (SA) of a response can have a more powerful effect on programming time, as indexed by reaction time and premotor time, than the number of movement parts in the response. The results of Experiment 2 revealed that the locus of the directional accuracy effect was SA and not target size or movement distance. In all three experiments, response SA was a better predictor of programming time than was number of movement parts, target size, movement distance, movement time, and average movement velocity. The findings support the notion that constraints placed upon movement initiation by the directional accuracy demand of the task can play an important role in determining the length of the programming process.

Effects of Average Movement Velocity on Reaction Time and Spatiotemporal Accuracy in Single-Aiming and Rapid-Timing Movement Tasks

The effects of instructed movement speed were investigated in two experiments. First, rapid-timing and single-aiming movement tasks were compared. Unlike rapid timing, single aiming implies spatial accuracy. The aim of the first experiment was twofold: (a) to examine whether the requirement of accurate placement termination in single aiming affects the negative relationship between instructed average velocity and reaction time found in rapid timing, and (b) to test the speed-accuracy relationships predicted by the symmetric impulse variability model of these movement tasks. For this purpose, four average velocities (5, 24, 75, and 140 cm/s) were investigated in both types of movement tasks in a two-choice reaction task. The effects of average velocity on reaction time were similar in both single-aiming and rapid-timing tasks, and the predicted linear relationship between instructed average velocity and spatial accuracy was not found. The results suggest that the movement control mode, that is, open loop or closed loop, interferes with effects of instructed average velocity. The movement control mode explanation was confirmed in the second experiment with respect to the effect of paired velocities on reaction time. It is argued that the type of movement control mode must be considered in the interpretation of effects of instructed average velocity on reaction time and spatiotemporal measures.

Fitts’ Law with an Isometric Controller

Twenty-four male subjects performed a discrete positioning task using an isometric controller. Two levels of order of control (position and velocity) were factorially crossed with two levels of control-display gain. Fitts' law functions were found for each of the four conditions. The velocity control conditions had significantly steeper slopes than the corresponding position control conditions, but there was no main effect for gain. A predicted interaction between control-display gain and order of control was found, indicating that the relative benefit of high gain is greater for velocity control than for position control. The reaction time (RT) regression lines had steeper negative slopes than those attained by Jagacinski, Repperger, Moran, Ward, and Glass (1980), who used an isotonic controller. This is in agreement with the results of Falkenberg and Newell (1980), who found that as average velocity increases, RT decreases. The components of Fitts' law were investigated, and this showed that the RT finding was due to the amplitude of the target, which covaried with average velocity, but was not due to the width.