Response force is sensitive to the temporal uncertainty of response stimuli

Temporal unpredictability increases error monitoring as revealed by EEG-EMG investigation

Reacting in an unpredictable context increases error monitoring as evidenced by greater error-related negativity (ERN), an electrophysiological marker linked to an evaluation of response outcomes. We investigated whether ERN also increased when participants evaluated their responses to events that appeared in unpredictable versus predictable moments in time. We complemented electroencephalographic (EEG) analysis of cortical activity by measuring performance monitoring processes at the peripheral level using electromyography (EMG). Specifically, we used EMG data to quantify how temporal unpredictability would affect motor time (MT), the interval between the onset of muscle activity, and the mechanical response. MT increases following errors, indexing online error detection, and an attempt to stop incorrect actions. In our temporally cued version of the stop-signal task, symbolic cues predicted (temporally predictable condition) or not (temporally unpredictable condition) the onset of a target. In 25% of trials, an auditory signal occurred shortly after the target presentation, informing participants that they should inhibit their response completely. Response times were slower, and fewer inhibitory errors were made during temporally unpredictable than predictable trials, indicating enhanced control of unwanted actions when target onset time was unknown. Importantly, the ERN to inhibitory errors was greater in temporally unpredictable relative to temporally predictable conditions. Similarly, EMG data revealed prolonged MT when reactions to temporally unpredictable targets had not been stopped. Taken together, our results show that a temporally unpredictable environment increases the control of unwanted actions, both at cortical and peripheral levels, suggesting a higher subjective cost of maladaptive responses to temporally uncertain events.

Influence of Mental Training of Attentional Control on Autonomic Arousal Within the Framework of the Temporal Preparation of a Force Task

While temporal preparation has frequently been examined through the manipulation of foreperiods, the role of force level during temporal preparation remains underexplored. In our study, we propose to manipulate mental training of attentional control in order to shed light on the role of the force level and autonomic nervous system in the temporal preparation of an action. Forty subjects, divided into mental training group (n = 20) and without mental training group (n = 20), participated in this study. The influence of the attentional control and force levels on the autonomic nervous system were measured using the skin conductance response and the heart rate variability; the accuracy of the motor responses was measured using a method derived from machine learning. Behaviorally, only the mental training group reinforced its motor and attentional control. When using short foreperiod durations and high force level, motor and attentional control decreased, consistent with the dominant sympathetic system. This resulted in an increased anticipation rate of responses with a higher reaction time compared to the long foreperiods duration and low force level, in which the reaction time significantly decreased, with enhancement of the expected force level, showing consistency with the dominant parasympathetic system. Interestingly, results revealed a predictive relationship between the sympathovagal balance and motor and attentional control during the long foreperiods and low force level. Finally, results demonstrate that attentional mental training leads to the reinforcement of interactions between the autonomic nervous system and attentional processes which are involved in the temporal preparation of a force task.

Attention to space and time: Independent or interactive systems? A narrative review

While there is ample evidence for the ability to selectively attend to where in space and when in time a relevant event might occur, it remains poorly understood whether spatial and temporal attention operate independently or interactively to optimize behavior. To elucidate this important issue, we provide a narrative review of the literature investigating the relationship between the two. The studies were organized based on the attentional manipulation employed (endogenous vs. exogenous) and the type of task (detection vs. discrimination). Although the reviewed findings depict a complex scenario, three aspects appear particularly important in promoting independent or interactive effects of spatial and temporal attention: task demands, attentional manipulation, and their combination. Overall, the present review provides key insights into the relationship between spatial and temporal attention and identifies some critical gaps that need to be addressed by future research.

Neurocognitive analyses reveal that video game players exhibit enhanced implicit temporal processing

Winning in action video games requires to predict timed events in order to react fast enough. In these games, repeated waiting for enemies may help to develop implicit (incidental) preparation mechanisms. We compared action video game players and non-video game players in a reaction time task involving both implicit time preparations and explicit (conscious) temporal attention cues. Participants were immersed in virtual reality and instructed to respond to a visual target appearing at variable delays after a warning signal. In half of the trials, an explicit cue indicated when the target would occur after the warning signal. Behavioral, oculomotor and EEG data consistently indicate that, compared with non-video game players, video game players better prepare in time using implicit mechanisms. This sheds light on the neglected role of implicit timing and related electrophysiological mechanisms in gaming research. The results further suggest that game-based interventions may help remediate implicit timing disorders found in psychiatric populations.

A cross-sectional EEG study reveals that individuals who consistently play action video games exhibit improved performance in a reaction time task involving implicit time preparations, compared with participants who did not normally play video games

Temporal expectancy modulates stimulus-response integration

We can use information derived from passing time to anticipate an upcoming event. If time before an event varies, responses towards this event become faster with increasing waiting time. This variable-foreperiod effect has been often observed in response-speed studies. Different action control frameworks assume that response and stimulus features are integrated into an event file that is retrieved later if features repeat. Yet the role of foreperiods has so far not been investigated in action control. Thus, we investigated the influence of foreperiod on the integration of action-perception features. Participants worked through a standard distractor-response binding paradigm where two consecutive responses are made towards target letters while distractor letters are present. Responses and/or distractors can repeat or change from first to second display, leading to partial repetition costs when only some features repeat or repetition benefits when all features repeat (the difference constituting distractor-response binding). To investigate the effect of foreperiod, we also introduced an anti-geometric distribution of foreperiods to the time interval before the first response display. We observed that distractor-response binding increased with increasing foreperiod duration, and speculate that this was driven by an increase in motor readiness induced by temporal expectancy.

Temporal preparation accelerates spatial selection by facilitating bottom-up processing

Temporal preparation facilitates spatial selection in visual search. This selection benefit has not only been observed for targets, but also for task-irrelevant, salient distractors. This result suggests that temporal preparation influences bottom-up salience in spatial selection. To test this assumption, we conducted an event-related-potential (ERP) study in which we measured the joint effect of temporal preparation and target salience on the N2pc as an index of spatial selection and the N1 as an index of perceptual discrimination. To manipulate target salience, we employed two different setsizes (i.e., a small or large number of homogeneous distractors). To manipulate temporal preparation, we presented a warning signal before the search display and we varied the length of the interval (foreperiod) between warning signal and search display in different blocks of trials (constant foreperiod paradigm). Replicating previous results, we observed that the N1 and the N2pc arose earlier in case of good temporal preparation. Importantly, the beneficial effect on the N2pc onset latency was stronger when the target salience was initially low (i.e., small setsize). This result provides evidence that temporal preparation influences bottom-up processing and, thereby, facilitates spatial selection.

The warning stimulus as retrieval cue: The role of associative memory in temporal preparation

In a warned reaction time task, the warning stimulus (S1) initiates a process of temporal preparation, which promotes a speeded response to the impending target stimulus (S2). According to the multiple trace theory of temporal preparation (MTP), participants learn the timing of S2 by storing a memory trace on each trial, which contains a temporal profile of the events on that trial. On each new trial, S1 serves as a retrieval cue that implicitly and associatively activates memory traces created on earlier trials, which jointly drive temporal preparation for S2. The idea that S1 assumes this role as a retrieval cue was tested across eight experiments, in which two different S1s were associated with two different distributions of S1-S2 intervals: one with predominantly short and one with predominantly long intervals. Experiments differed regarding the S1 features that made up a pair, ranging from highly distinct (e.g., tone and flash) to more similar (e.g., red and green flash) and verbal (i.e., "short" vs "long"). Exclusively for pairs of highly distinct S1s, the results showed that the S1 cue modified temporal preparation, even in participants who showed no awareness of the contingency. This cueing effect persisted in a subsequent transfer phase, in which the contingency between S1 and the timing of S2 was broken - a fact participants were informed of in advance. Together, these findings support the role of S1 as an implicit retrieval cue, consistent with MTP.

Neural correlates of error detection during complex response selection: Introduction of a novel eight-alternative response task

Error processing in complex decision tasks should be more difficult compared to a simple and commonly used two-choice task. We developed an eight-alternative response task (8ART), which allowed us to investigate different aspects of error detection. We analysed event-related potentials (ERP; N = 30). Interestingly, the response time moderated several findings. For example, only for fast responses, we observed the well-known effect of larger error negativity (N_e) in signalled and non-signalled errors compared to correct responses, but not for slow responses. We identified at least two different error sources due to post-experimental reports and certainty ratings: impulsive (fast) errors and (slow) memory errors. Interestingly, the participants were able to perform the task and to identify both, impulsive and memory errors successfully. Preliminary evidence indicated that early (N_e-related) error processing was not sensitive to memory errors but to impulsive errors, whereas the error positivity seemed to be sensitive to both error types.

Mechanisms of Impulsive Responding to Temporally Predictable Events as Revealed by Electromyography

Temporal predictability optimises behaviour when a simple response is required, as demonstrated by faster reaction times (RTs) and higher accuracy. However, its beneficial effects come at a cost under situations of response conflict. Here, we investigated the motor underpinnings of behaviour to temporally predictable events in the Simon conflict task. We compared motor responses to lateralised targets whose position conflicted (incompatible condition) or not (compatible condition) with the hand of response. Importantly, electromyographic (EMG) recordings allowed us to study "partial errors", defined as subthreshold muscle activity in the incorrect response agonist preceding a correct response. Advanced distributional analyses coupled with EMG data revealed that temporal predictability induced impulsive premature responding, as indexed by increased likelihood of fast incorrect EMG activations (both partial errors and errors) to incompatible targets. In parallel, responding to temporally predictable targets speeded the latency of partial errors, further indicating that temporal predictability increased the tendency to act prematurely. There was, however, no effect of temporal predictability on subsequent suppression of partial errors. Our results provide direct evidence that temporal predictability acts by increasing the urge to initiate a fast, yet potentially erroneous, response. This mechanism parsimoniously explains both beneficial effects of temporal predictability when no conflict in the environment is present, as well as its costs when more complex motor behaviour is required.

Having your cake and eating it: Faster responses with reduced muscular activation while learning a temporal interval

We examined how motor responses to a stimulus evolve as individuals learn to predict when a stimulus will appear, by comparing responses to a regular versus irregular stimulus train. The study was conducted with two groups of adults - one responded to the regular appearance of a visual stimulus every 3 s (R group) and the second responded to the irregular presentation of the same stimulus (IR group) at intervals varying between 2 and 4 s. Participants responded to the appearance of the stimulus by bending over to press a button that was slightly out of reach. This whole body reach requires muscular activation at the ankles. Over the course of 50 consecutive responses, the response times in the R group were found to decrease more than those for participants in the IR group. The electromyographs (EMGs) of two ankle antagonist muscles, the anterior tibialis and soleus were also modified as participants progressively learnt the temporal regularity of a sequence. Tibialis onset times for the R group were found to decrease faster. A less predictable observation was the faster reduction in post stimulus activation of the tibialis muscle for the R group. Soleus muscle deactivation is an indicator of movement preparation. EMG integrals for this muscle a little before stimulus onset showed a trend for greater decrease in the R group. In summary, our study shows that temporal expectations over repeated stimulus presentation permit the dynamic optimization of motor activity with progressively faster response times, muscle activation onset times and lower muscle activation amplitudes.

Effects of aging on temporal predictive mechanisms of speech and hand motor reaction time

Evidence from previous studies has suggested that movement execution in younger adults is accelerated in response to temporally predictable vs. unpredictable sensory stimuli. This effect indicates that external temporal information can modulate motor behavior; however, how aging can influence temporal predictive mechanisms in motor system has yet to be understood. The objective of the present study was to investigate aging effects on the initiation and inhibition of speech and hand movement reaction times in response to temporally predictable and unpredictable sensory stimuli. Fifteen younger (mean age 22.6) and fifteen older (mean age 63.8) adults performed a randomized speech vowel vocalization or button press initiation and inhibition tasks in two counterbalanced blocks in response to temporally predictable and unpredictable visual cue stimuli. Results showed that motor reaction time was accelerated in both younger and older adults for predictable vs. unpredictable stimuli during initiation and inhibition of speech and hand movement. However, older adults were significantly slower than younger adults in motor execution of speech and hand movement when stimulus timing was unpredictable. Moreover, we found that overall, motor inhibition of speech and hand was executed faster than their initiation. Our findings suggest that older adults can compensate age-related decline in motor reaction times by incorporating external temporal information and execute faster movement in response to predictable stimuli, whereas unpredictable temporal information cannot counteract aging effects efficiently and lead to less accurate motor timing predictive codes for speech production and hand movement.

Dissociating Explicit and Implicit Timing in Parkinson's Disease Patients: Evidence from Bisection and Foreperiod Tasks

A consistent body of literature reported that Parkinson's disease (PD) is marked by severe deficits in temporal processing. However, the exact nature of timing problems in PD patients is still elusive. In particular, what remains unclear is whether the temporal dysfunction observed in PD patients regards explicit and/or implicit timing. Explicit timing tasks require participants to attend to the duration of the stimulus, whereas in implicit timing tasks no explicit instruction to process time is received but time still affects performance. In the present study, we investigated temporal ability in PD by comparing 20 PD participants and 20 control participants in both explicit and implicit timing tasks. Specifically, we used a time bisection task to investigate explicit timing and a foreperiod task for implicit timing. Moreover, this is the first study investigating sequential effects in PD participants. Results showed preserved temporal ability in PD participants in the implicit timing task only (i.e., normal foreperiod and sequential effects). By contrast, PD participants failed in the explicit timing task as they displayed shorter perceived durations and higher variability compared to controls. Overall, the dissociation reported here supports the idea that timing can be differentiated according to whether it is explicitly or implicitly processed, and that PD participants are selectively impaired in the explicit processing of time.

Comparing the effects of implicit and explicit temporal expectation on choice response time and response conflict

People can use temporally structured sensory information to anticipate future events. Temporal information can be presented implicitly through probability manipulation without participants' awareness of the manipulation, or explicitly conveyed through instructions. We examined how implicit and explicit temporal information established temporal expectations that influenced choice response times and response conflict (measured as flanker effects). We implicitly manipulated temporal structure by block-wise varying the likely timing of a target. In the short-interval block, a target was presented frequently (80 % of trials) after a short (400 ms) cue-to-target interval and infrequently (20 % of trials) after a long (1200 ms) interval; the probability assignment was reversed in the long-interval block. Building on this baseline condition (Experiment 1), we augmented the temporal information by filling the cue-to-target intervals with tones (Experiment 2), explicitly informed participants of the prevalent time interval (Experiment 3) and provided trial-by-trial reminders of the prevalent time interval (Experiment 4). The temporal probability manipulation alone (of which participants were unaware) influenced choice response times but only when the temporal information was augmented with tones, whereas providing the explicit knowledge of the temporal manipulation, with or without trial-by-trial reminders, robustly influenced choice response times. Response conflict was unaffected by these conditions. These results suggest that temporal expectation can be established by the implicit learning of a temporal structure given that sufficiently strong temporal information is presented as well as by the explicit knowledge of the temporal structure. This established temporal expectation influences choice response times without necessarily affecting the strength of response conflict.

Action history influences subsequent movement via two distinct processes

The characteristics of goal-directed actions tend to resemble those of previously executed actions, but it is unclear whether such effects depend strictly on action history, or also reflect context-dependent processes related to predictive motor planning. Here we manipulated the time available to initiate movements after a target was specified, and studied the effects of predictable movement sequences, to systematically dissociate effects of the most recently executed movement from the movement required next. We found that directional biases due to recent movement history strongly depend upon movement preparation time, suggesting an important contribution from predictive planning. However predictive biases co-exist with an independent source of bias that depends only on recent movement history. The results indicate that past experience influences movement execution through a combination of temporally-stable processes that are strictly use-dependent, and dynamically-evolving and context-dependent processes that reflect prediction of future actions.

Fragile temporal prediction in patients with schizophrenia is related to minimal self disorders

Patients with schizophrenia have difficulty in making sensory predictions, in the time domain, which have been proposed to be related to self-disorders. However experimental evidence is lacking. We examined both voluntary and automatic forms of temporal prediction in 28 patients and 24 matched controls. A visual cue predicted (temporal cue) or not (neutral cue) the time (400 ms/1000 ms) at which a subsequent target was presented. In both patients and controls, RTs were faster for targets presented after long versus short intervals due to the temporal predictability inherent in the elapse of time ("hazard function"). This RT benefit was correlated with scores on the EASE scale, which measures disorders of the self: patients with a high 'self-awareness and presence' score did not show any significant benefit of the hazard function, whereas this ability was preserved in patients with a low score. Moreover, all patients were abnormally sensitive to the presence of "catch" trials (unexpected absence of a target) within a testing block, with RTs actually becoming slower at long versus short intervals. These results indicate fragility in patients' ability to continuously extract temporally predictive information from the elapsing interval. This deficit might contribute to perturbations of the minimal self in patients.

Dissociations of spatial congruence effects across response measures: an examination of delta plots

Spatial congruence ("Simon") effects on reaction time (RT) and response force (RF) were studied in two experiments requiring speeded choice responses to the color of a stimulus located irrelevantly to the left or right of fixation. In Experiment 1 with unimanual responses, both RT and incorrect-hand RF were sensitive to spatial congruence, and both showed larger Simon effects following a congruent trial than following an incongruent one. RT and incorrect-hand RF were dissociated in distributional (i.e., delta plot) analyses, however. As in previous studies, the Simon effect on RT was largest for the fastest responses and diminished as RT increased (i.e., decreasing delta plot). In contrast, Simon effects on RF did not decrease for slower responses; if anything, they increased slightly. In Experiment 2 participants made bimanual responses, allowing measurement of the spatial congruence effect for each trial. Responses were both faster and more forceful with the spatially congruent hand than with the spatially incongruent one, but neither of these effects decreased for slower responses. Overall, the results demonstrate that at least some motor-level effects of irrelevant spatial location persist for slower responses.

Trial-by-trial updating of an internal reference in discrimination tasks: evidence from effects of stimulus order and trial sequence

In psychophysics, participants are often asked to discriminate between a constant standard and a variable comparison. Previous studies have shown that discrimination performance is better when the comparison follows, rather than precedes, the standard. Prominent difference models of psychophysics and decision making cannot easily explain this order effect. However, a simple extension of this model class involving dynamical updating of an internal reference accounts for this order effect. In addition, this Internal Reference Model (IRM) predicts sequential response effects. We examined the predictions of IRM in two duration discrimination experiments. The obtained results are in agreement with the predictions of IRM, suggesting that participants update their internal reference on every trial. Additional simulations show that IRM also accounts for the negative sequential effects observed in single-stimulus paradigms.

Effects of response force parameters on medial-frontal negativity

The response-related medial-frontal activity (MFN) is often supposed to reflect action-monitoring and error-processing activity. The present force-production task was designed to investigate the effects of two response parameters (i.e., peak response force and time-to-peak, TTP) on the MFN separately. In a 2 × 2 design (high vs. low target force and short vs. long TTP), 22 participants had to produce isometric force pulses to match one of four conditions (e.g., a high target force with a long TTP). Significant main effects of both target force and target TTP were revealed. As previously shown, the MFN amplitude was higher in the high target-force condition than in the low target-force condition. Contrary to the initial expectations, a long TTP had the effect of reducing the MFN amplitude. There was no error-specific effect on the MFN. The force-unit monitoring model (FUMM) is suggested to account for the force- and TTP- specific variations of MFN amplitude, latency and slope.

The Temporal Dynamics of Effect Anticipation in Course of Action Planning

“Strong” versions of the ideomotor theory of action control claim that anticipations of the environmental effects that actions bring about are mandatory for response selection. This is considered to be the one and only way of how actions can be voluntarily selected. We studied this notion in a series of four experiments where we adapted the flanker paradigm to investigate the involvement of effect codes in the preparation of motor responses. Participants first learned that their responses to stimulus letters were contingently followed by the presentation of a new letter on the screen. In the second phase of the experiments, the action-demanding letters were presented together with the effects of the correct response, effects of other responses, or neutral letters. Varying the stimulus onset asynchrony (SOA) between target stimuli and the flanking effect stimuli provides the opportunity to investigate the temporal dynamics of the activation of effect codes. Hence, flanker stimuli were presented before, simultaneously with, or after the onset of the target. The results indicate that effect-related information from the flanker stimuli is involved in the preparation process, but mainly in later phases of response preparation. The observed pattern of results suggests that, at least under conditions where responses are determined by stimuli, effect codes are activated in course of response planning to enable the evaluation of the executed response and the monitoring of response execution, but they do not automatically activate the responses themselves.

Temporal Preparation Decreases Perceptual Latency: Evidence from a Clock Paradigm

A clock paradigm was employed to assess whether temporal preparation decreases the time to detect the onset of a stimulus—that is, perceptual latency. In four experiments participants watched a revolving clock hand while listening to soft or loud target tones under high or low temporal preparation. At the end of each trial, participants reported the clock hand position at the onset of the target tone. The deviation of the reported clock hand position from the actual position indexed perceptual latency. As expected, perceptual latency decreased with target tone intensity. Most importantly, however, greater temporal preparation decreased perceptual latency in all four experiments, especially for soft tones, which supports rather directly the idea that temporal preparation diminishes the duration of perceptual processing.

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.

When Time Shapes Behavior: fMRI Evidence of Brain Correlates of Temporal Monitoring

Time processing may shape behavior in several ways, although the underlying neural correlates are still poorly understood. When preparatory intervals between stimuli vary randomly in a block, for instance, responses are faster as the interval gets longer. This effect, known as variable foreperiod (FP) effect, has been attributed to a process monitoring the conditional probability of stimulus occurrence as the interval increases. Previous evidence points to the right dorsolateral prefrontal cortex (DLPFC) as a possible node for this time-monitoring process. The present study addresses this hypothesis with functional magnetic resonance imaging (fMRI). Block-design fMRI was used on 14 young participants while they performed a visual discrimination task with fixed and variable preparatory intervals (FPs) of 1 and 3 sec. In the variable versus fixed FP contrast, the right DLPFC and a visual area were more activated in the subgroup of participants who showed a reliable variable FP effect than in another subgroup who did not show that effect. Only the activation in the right DLPFC was supported by a significant interaction between FP condition (variable vs. fixed) and group. This finding may reflect possible differences in the strategy adopted by the two subgroups of participants while performing the task. Although results suggest that many brain areas may be involved in preparation over time, the role of the right DLPFC is critical to observe the strategically mediated behavioral effects in the variable FP paradigm.

The Effects of Accessory Stimuli on Information Processing: Evidence from Electrophysiology and a Diffusion Model Analysis

People typically respond faster to a stimulus when it is accompanied by a task-irrelevant accessory stimulus presented in another perceptual modality. However, the mechanisms responsible for this accessory-stimulus effect are still poorly understood. We examined the effects of auditory accessory stimulation on the processing of visual stimuli using scalp electrophysiology (Experiment 1) and a diffusion model analysis (Experiment 2). In accordance with previous studies, lateralized readiness potentials indicated that accessory stimuli do not speed motor execution. Surface Laplacians over the motor cortex, however, revealed a bihemispheric increase in motor activation—an effect predicted by nonspecific arousal models. The diffusion model analysis suggested that accessory stimuli do not affect parameters of the decision process, but expedite only the nondecision component of information processing. Consequently, we conclude that accessory stimuli facilitate stimulus encoding. The visual P1 and N1 amplitudes on accessory-stimulus trials were modulated in a way that is consistent with multisensory energy integration, a possible mechanism for this facilitation.

Sequential effects within a short foreperiod context: evidence for the conditioning account of temporal preparation

Responses to an imperative stimulus (IS) are especially fast when they are preceded by a warning signal (WS). When the interval between WS and IS (the foreperiod, FP) is variable, reaction time (RT) is not only influenced by the current FP but also by the FP of the preceding trial. These sequential effects have recently been proposed to originate from a trace conditioning process, in which the individuals learn the temporal WS-IS relationship in a trial-by-trial manner. Research has shown that trace conditioning is maximal when the temporal interval between the conditioned and unconditioned stimulus is between 0.25 and 0.60s. Consequently, one would predict that sequential effects occur especially within short FP contexts. However, this prediction is contradicted by Karlin [Karlin, L. (1959). Reaction time as a function of foreperiod duration and variability. Journal of Experimental Psychology, 58, 185-191] who did not observe the typical sequential effects with short FPs. To investigate temporal preparation for short FPs, three experiments were conducted, examining the sequential FP effect comparably for short and long FP-sets (Experiment 1), assessing the influence of catch trials (Experiment 2) and the case of a very dense FP-range (Experiment 3) on sequential FP effects. The results provide strong evidence for sequential effects within a short FP context and thus support the trace conditioning account of temporal preparation.

The dual nature of time preparation: neural activation and suppression revealed by transcranial magnetic stimulation of the motor cortex

Single-pulse transcranial magnetic stimulations (TMSs) of the motor cortex (M1) were performed in order to decipher the neural mechanisms of time preparation. We varied the degree to which it was possible to prepare for the response signal in a choice reaction time (RT) task by employing either a short (500 ms) or a long (2500 ms) foreperiod in separate blocks of trials. Transcranial magnetic stimulations were delivered during these foreperiods in order to study modulations in both the size of the motor evoked potential (MEP) and the duration of the silent period (SP) in tonically activated response agonists. Motor evoked potential area and silent period duration were assumed to reflect, respectively, the excitability of the cortico-spinal pathway and the recruitment of inhibitory cortical interneurons. Shorter reaction times were observed with the shorter foreperiod, indicating that a better level of preparation was attained for the short foreperiod. Silent period duration decreased as time elapsed during the foreperiod and this decrement was more pronounced for the short foreperiod. This result suggests that time preparation is accompanied by a removal of intracortical inhibition, resulting in an activation. Motor evoked potential area decreased over the course of the short foreperiod, but not over the long foreperiod, revealing that time preparation involves the inhibition of the cortico-spinal pathway. We propose that cortico-spinal inhibition secures the development of cortical activation, preventing erroneous premature responding.

Temporal uncertainty degrades perceptual processing

When participants are required to react to a stimulus, reaction times (RTs) are usually reduced when temporal uncertainty about stimulus occurrence is minimized. Contrary to the common assumption attributing this RT benefit solely to the speeding of motor processes, recent evidence suggests that temporal uncertainty might rather influence premotoric processing levels. We employed a backward-masking procedure to further confine the locus of the temporal uncertainty effect. Participants performed a discrimination task and indicated whether a spatial gap within a square was on the right or the left side. In addition to the shorter RTs, visual discrimination accuracy was improved when temporal uncertainty was low. This result demonstrates that temporal uncertainty influences stimulus processing at a perceptual level.

Knowing when to respond and the efficiency of the cortical motor command: A Laplacian ERP study

The objective was to test whether motor preparation can modulate the efficiency of the cortical motor command. The electroencephalogram (EEG) was recorded from electrodes located over the primary sensorimotor cortices during the performance of a between-hand choice reaction time task in which foreperiod duration (the interval between the warning and the imperative signals, 800 vs. 2800 ms) was varied across blocks of trials. In order to increase the spatial resolution of the EEG traces, surface Laplacian was estimated. The amplitude of the negative wave developing over the hemisphere contralateral to the response was smaller for the short foreperiod associated with the best performance level. These results indicate that the activation of the primary sensorimotor cortex involved in the response is less pronounced for the short foreperiod, suggesting that temporal advance information increases the efficiency of the cortical motor command.

The locus of temporal preparation effects: Evidence from the psychological refractory period paradigm

In reaction time (RT) tasks, responses are especially fast when participants can anticipate the onset of an imperative response signal. Although this RT facilitation is commonly attributed to temporal preparation, it is unclear whether this preparation shortens the duration of early or late processes. We used the effect propagation property of the psychological refractory period paradigm to localize the effect of temporal preparation. Manipulation of temporal uncertainty affected the RT of Task 1, regardless of the level of stimulus onset asynchrony (SOA). Consistent with the prediction of an early locus of temporal preparation, this effect propagated completely to the RT of Task 2 at short SOAs, but propagation diminished virtually to zero at long SOAs.

Temporal uncertainty does not affect response latencies of movements produced during startle reactions

Previous research has shown that a startle 'go' stimulus, presented at a constant latency with respect to a warning stimulus, is capable of eliciting an intended voluntary movement in a simple reaction time (RT) task at very short latencies without involvement of the cerebral cortex (Carlsen et al. in Exp Brain Res 152:510-518, 2003; J Motor Behav 36:253-264, 2004a; Exp Brain Res 159:301-309 2004b; Valls-Solé et al. in J Physiol 516:931-938, 1999). The purpose of the present experiment was to determine the effect of temporal uncertainty on response latency during an RT task that comprised a startle stimulus. Participants were required to perform an active 20 degrees wrist extension movement in response to an auditory tone that was presented 2,500 to 5,500 ms after a warning stimulus, in 1,000 ms increments. On certain trials the control auditory stimulus (80 dB) was unexpectedly replaced by the startle stimulus (124 dB). When participants were startled the intended voluntary movement was initiated at approximately 70 ms, regardless of foreperiod duration. The magnitude and invariance of response latencies to the startle stimulus suggest that the intended movement had indeed been prepared prior to the arrival of the imperative go stimulus, within 2.5 s of the warning stimulus. Furthermore, there was no evidence that the prepared movement decayed over a period of at least 3 s.

Interrupting timing in interval production and discrimination: Similarities and differences

Interruptions in human timing have been studied in the last few years using temporal production and discrimination tasks. Expecting a break shortened perceived duration in both paradigms but manipulating break duration affected time production only, suggesting that preparatory processes might not take place in time discrimination. In time production, using cues revealed that providing information about the break may modulate the effect of break expectancy. For example, time was perceived as shorter when a break was expected in trials with no breaks, but forewarning participants of the break absence with a cue almost abolished the effect. In the present experiment, a tone was classified as "short" or "long" in a discrimination task. Location and duration of breaks were varied and cues were provided in some trials with no breaks. Results showed an effect of break expectancy: perceived duration shortened with increasing pre-break duration. Reducing expectancy with cues in uninterrupted tones decreased the proportion of "short" responses in long-tone trials, but not in short-tone trials. As in previous discrimination experiments, perceived duration was unaffected by varying break duration. Similarities and differences in results as well as in their interpretation when breaks are used in time production and time discrimination tasks are discussed.

Accessory stimulation in the time course of visuomotor information processing: stimulus intensity effects on reaction time and response force

A series of three visual choice-reaction time experiments were performed to systematically investigate the effects of accessory auditory stimulation on response time (RT) and response force (RF). In Experiment 1, the effect of accessory auditory stimulation on early visual information processing was investigated. Experiments 2 and 3 were designed to examine the effects of accessory intensity on RT and RF across the entire time course of sensorimotor processing. Accessory stimulation accelerated response speed only when presented within 100 ms after onset of the visual response signal. An enhancing effect of accessory stimulation on RF, however, was found as late as 220 ms after onset of the response signal. These findings support the notion that response speed and response dynamics represent functionally independent sensorimotor phenomena.

An Electromyographic Examination of Response Execution and Inhibition in Between-Hand Choice Reaction Time

Abstract: In between-hand choice reaction time (RT) tasks, the activation of the cerebral motor structures involved in the required response is accompanied by an inhibition of the structures involved in the alternative response. The objectives were (1) to check whether the inhibition observed at the central level can be accompanied by signs of deactivation at the peripheral level during response execution and (2) to assess whether time preparation affects response execution. Surface electromyographic (EMG) activity of the first dorsal interosseus was recorded during the performance of a between-hand choice visual RT task in which the foreperiod duration was manipulated. The contraction of the muscle involved in the required response was accompanied by a reduction in the EMG activity of the muscle involved in the nonrequired response. The foreperiod duration influenced this EMG pattern. The findings reveal peripheral signs of a deactivation of the non-required response and suggest that time preparation influences the activity of the muscles involved in both the required and the nonrequired response. The present results are compatible with the view that, at least in between-hand choice RT tasks, the motor command specifies both the activation of the central structures involved in the required response and the inhibition of the central structures involved in the nonrequired response. They further indicate that time preparation affects the activity of the response agonists.

Intentional and Unintentional Contributions to Nonspecific Preparation: Electrophysiological Evidence

The authors hypothesized that there are distinct intentional and unintentional influences on nonspecific preparation for a future event. In 2 experiments, participants responded to an imperative stimulus (S-sub-2) that was presented equiprobably either 400 ms or 1,200 ms after the offset of a warning stimulus (S-sub-1). During the S-sub-1-S-sub-2 interval, the authors measured the contingent negative variation (CNV), an event-related brain potential reflecting nonspecific preparation. S-sub-1 provided either no information or reliable information about the duration of the impending S-sub-1-S-sub-2 interval, thereby allowing an intentional influence on the state of preparation. The effect of S-sub-1 information on the CNV was approximately additive to the effect of the S-sub-1-S-sub-2 interval that was used on the preceding trial. This supports the view that the preceding S-sub-1-S-sub-2 interval contributes unintentionally to the state of nonspecific preparation guided by a process of trace conditioning.

Independence of reaction time and response force control during isometric leg extension

In this study, we examined the relative control of reaction time and force in responses of the lower limb. Fourteen female participants (age 21.2 +/- 1.0 years, height 1.62 +/- 0.05 m, body mass 54.1 +/- 6.1 kg; mean +/- s) were instructed to exert their maximal isometric one-leg extension force as quickly as possible in response to an auditory stimulus presented after one of 13 foreperiod durations, ranging from 0.5 to 10.0 s. In the 'irregular condition' each foreperiod was presented in random order, while in the 'regular condition' each foreperiod was repeated consecutively. A significant interactive effect of foreperiod duration and regularity on reaction time was observed (P < 0.001 in two-way ANOVA with repeated measures). In the irregular condition the shorter foreperiod induced a longer reaction time, while in the regular condition the shorter foreperiod induced a shorter reaction time. Peak amplitude of isometric force was affected only by the regularity of foreperiod and there was a significant variation of changes in peak force across participants; nine participants were shown to significantly increase peak force for the regular condition (P < 0.001), three to decrease it (P < 0.05) and two showed no difference. These results indicate the independence of reaction time and response force control in the lower limb motor system. Variation of changes in peak force across participants may be due to the different attention to the bipolar nature of the task requirements such as maximal force and maximal speed.