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Stimulus contrast and duration effects on visual temporal integration and order judgment were examined in a unified paradigm. Stimulus onset asynchrony was governed by the duration of the first stimulus in Experiment 1, and by the interstimulus interval in Experiment 2. In Experiment 1, integration and order uncertainty increased when a low contrast stimulus followed a high contrast stimulus, but only when the second stimulus was 20 or 30 ms. At 10 ms duration of the second stimulus, integration and uncertainty decreased. Temporal order judgments at all durations of the second stimulus were better for a low contrast stimulus following a high contrast one. By contrast, in Experiment 2, a low contrast stimulus following a high contrast stimulus consistently produced higher integration rates, order uncertainty, and lower order accuracy. Contrast and duration thus interacted, breaking correspondence between integration and order perception. The results are interpreted in a tentative conceptual framework.

In accordance with a rational model of study-time investment, we previously found that the prospect of a resit exam leads to lower investments of fictional study-time for a first exam opportunity in an investment game utilizing simulated exams. In the current study, we investigated whether the depreciation of one's first-exam investment reduces the resit effect. Specifically, we investigated study-time investments for a simulated multiple-choice exam in which 0, 50, or 100% of the initial study-time investment was lost before the resit exam. In accordance with our predictions, we found that the magnitude of the resit effect decreased as investment depreciation increased. This finding suggests that the negative effect of resit exams on study-time investment may be countered by creating conditions under which investment depreciation (i.e. forgetting) is expected to occur, for instance, by increasing the temporal interval between the first attempt and resit exam.

In everyday tasks, people pick up and exploit temporal regularities in their environment. To optimize this process, it has been suggested that the attentional system prioritizes information that contains some form of structure. Indeed, Zhao et al. (2013) found that attention was biased towards the location and low-level visual features of shapes that appeared with a regular order but were not relevant for the task at hand. The goal of the current study was to investigate whether this bias also holds for implicit and irrelevant temporal regularities. In two experiments, participants were asked to perform search tasks in which a target appeared in one of four locations. In the first experiment, a sequence of squares was presented in between the search trials in the same four locations. Crucially, in one location, the square appeared with a regular rhythm. In the second experiment, a sequence of colored circles was presented in between the search trials, of which one specific colored circle appeared regularly. We expected that, if attention is automatically biased towards these temporal regularities, reaction times would be faster if the target matches the location or color of the regular stimulus. However, in both experiments, we found no such attentional bias. These results suggest that, although people might keep track of implicit temporal regularities, they do not use this information to guide their attention in the same way as order regularities.

Although many educational institutions allow students to resit exams, a recently proposed mathematical model suggests that this could lead to a dramatic reduction in study-time investment, especially in rational students. In the current study, we present a modification of this model in which we included some well-justified assumptions about learning and performance on multiple-choice tests, and we tested its predictions in two experiments in which participants were asked to invest fictional study time for a fictional exam. Consistent with our model, the prospect of a resit exam was found to promote lower investments of study time for a first exam and this effect was stronger for participants scoring higher on the cognitive reflection test. We also found that the negative effect of resit exams on study-time investment was attenuated when access to the resit was made uncertain by making it probabilistic or dependent on obtaining a minimal, non-passing grade for the first attempt. Taken together, these results suggest that offering students resit exams may compromise the achievement of learning goals, and they raise the more general implication that second chances promote risky behavior.

The processing of successive targets requires that attention be engaged and disengaged. Whereas attentional engagement can be studied by means of the N2pc component of the event-related potential (ERP), no ERP component has been linked to attentional disengagement. Here, we report the finding of such a component using an RSVP paradigm with multiple, successive targets and with a spatial-cuing paradigm. In both experiments, disengagement of attention was necessary to attend to subsequent targets. A distinct waveform following the N2pc, which we call the P4pc (Positivity 400 ms post-target posterior contralateral), was found. The P4pc was found when a lateralized cue indicated that attention would be needed for the processing of a target at either the same or a different location as the cue, but not when only the cue was to be responded to, indicating that the need to disengage attention is a prerequisite for the P4pc to occur. We expect the P4pc to provide a valuable addition to the set of electrophysiological measures used to study the dynamics and mechanisms of visual attention and visual search. (C) 2011 Elsevier B.V. All rights reserved.

Lien, Ruthruff, Remington, & Johnston (2005) reported residual switch cost differences between stimulus response (S-R) pairs and proposed the partial-mapping preparation (PMP) hypothesis, which states that advance preparation will typically be limited to a subset of S-R pairs because of structural capacity limitations, to account for these differences. Alternatively, the failure-to-engage (FTE) hypothesis does not allow for differences in probability of advance preparation between S-R pairs within a set; it accounts for residual switch cost differences by assuming that benefits of advance preparation may differ between S-R pairs. Three Experiments were designed to test between these hypotheses. No capacity limitations of the type assumed by the PMP hypothesis were found for many participants in Experiment 1. In Experiments 2 and 3, no evidence was found for the dependency of residual switch cost differences between S-R pairs on response-stimulus interval that is predicted by the PMP hypothesis. Mixture-model analysis of reaction times distributions in Experiment 3 provided strong support for the FTE hypothesis over the PMP hypothesis. Simulation studies with a computational implementation of the FIE hypothesis showed that it is able to account in great detail for the results of the present study. Together, these results provide strong evidence against the PMP hypothesis and support the FTE hypothesis that advance preparation probabilistically fails or succeeds at the level of the task set.

Frequency tagging is an EEG method based on the quantification of the steady state visual evoked potential (SSVEP) elicited from stimuli which flicker with a distinctive frequency. Because the amplitude of the SSVEP is modulated by attention such that attended stimuli elicit higher SSVEP amplitudes than do ignored stimuli, the method has been used to investigate the neural mechanisms of spatial attention. However, up to now it has not been shown whether the amplitude of the SSVEP is sensitive to gradations of attention and there has been debate about whether attention effects on the SSVEP are dependent on the tagging frequency used. We thus compared attention effects on SSVEP across three attention conditions-focused, divided, and ignored-with six different tagging frequencies. Participants performed a visual detection task (respond to the digit 5 embedded in a stream of characters). Two stimulus streams, one to the left and one to the right of fixation, were displayed simultaneously, each with a background grey square whose hue was sine-modulated with one of the six tagging frequencies. At the beginning of each trial a cue indicated whether targets on the left, right, or both sides should be responded to. Accuracy was higher in the focused- than in the divided-attention condition. SSVEP amplitudes were greatest in the focused-attention condition, intermediate in the divided-attention condition, and smallest in the ignored-attention condition. The effect of attention on SSVEP amplitude did not depend on the tagging frequency used. Frequency tagging appears to be a flexible technique for studying attention. (C) 2009 Elsevier B.V. All rights reserved.

Different aspects of preparation, especially processes related to knowing what to prepare versus applying that foreknowledge effectively, may be reflected in different types of brain activity, e.g., the lateralized readiness potential (LRP), beta-band event-related desynchronization and phase locking. In a previous study in which subjects had to switch between response hands, dissociations were found between types of preparatory hand-related lateralization in evoked potentials, amplitude and phase locking (Gladwin et al., 2006) knowing what task set to switch to and effectively preparing that task set affected the different measures of lateralization. Similarly to how, in task switching, stimuli and responses must be correctly related to each other, in the preparation of movement sequences relations must be specified concerning motor processes. Similar dissociations as found in the task switching data might then be found in a cued movement sequence task. This possibility was explored by precueing elements of a two-movement sequence involving the left and right index fingers, and comparing various measures of electroencephalogram activity. Cues could specify the full sequence, either the first or the second element, or neither element. Knowing the first. element was sufficient to lateralize the pattern of phase locking, but effects were found in the LRP and lateralized amplitude only when the full sequence was known. It seems likely that subjects only fully prepared the first response when they had full knowledge of the sequence so that the dissociation may be closely related to that found for task switching. Thus, the present data would appear to agree with previous results that couple response-foreknowledge with phase locking and the transformation of that foreknowledge into effective changes in component processes with evoked potential shifts. The results further underscore the general importance of considering different types of brain activity: depolarization, desynchronization and phase locking all appear to be involved in different aspects of cognitive control. (c) 2007 Elsevier Masson SrI. All rights reserved.

A sentence verification task (SVT) was used to test whether differences in neural activation patterns that have been attributed to IQ may actually depend on differential strategy use between IQ groups. Electroencephalograms were recorded from 14 low (89

Lateralized readiness potential (LRP) and time-frequency domain LRP-type measures, called motor-related amplitude asymmetries (MRAA), in the mu band (9-13 Hz; mu-MRAA) and the beta band (18-26 Hz; beta-MRAA) were used to study the time course of preparation in a task-switching task and a response precuing task. Several dissociations between LRP and mu-MRAA and beta-MRAA were found. Mu-MRAA and beta-MRAA, but not LRP, exhibited an early and strong reversal in cortical lateralization when advance preparation for a switch of response hand was required. LRP, but not mu-MRAA or beta-MRAA, was sensitive to manipulation of the probability that advance preparation of response hand would be useful in a response precuing task. These dissociations replicate earlier findings and suggest that movement-related cortical rhythms and cortical potentials are associated with distinct preparatory component processes that differ in terms of level of abstraction and effort, in line with similar functional distinctions between component processes underlying executive control in task switching. This suggests that a fine-grained analysis of subprocesses involved in motor control may provide important guiding principles for the study and understanding of levels and mechanisms of cognitive control. (c) 2006 Elsevier B.V. All rights reserved.

The instantaneous amplitude of the theta and alpha bands of the electroencephalogram (EEG) was studied during preparation periods in a task-switching experiment. Subjects had to switch between tasks in which they were to respond to either the visual or the auditory component of the stimulus. 11-13 Hz occipital amplitude increased prior to auditory, relative to visual repetition trials. The effect was transient, ending well before presentation of the stimulus that was being prepared for. Alternation trials were preceded by an increase in occipital theta-band activity, relative to repetition trials, for the visual task. This effect was also transient. The effects suggest tentative hypotheses for the function of transient bursts of alpha- and theta-band oscillations and indicate the possibility of a psychophysiological resolution of theoretical questions concerning the origin of switch costs. (C) 2004 Elsevier B.V. All rights reserved.

We argue that a general control process, responsible for the activation and maintenance of task goals, is central to the concept of executive function. Failures of this process can become manifest as goal neglect: disregard of a task requirement even though it has been understood (Duncan, 1995). We discuss the results of several published and new experiments using various versions of the anti-saccade task in order to investigate the circumstances under which goal neglect is likely to occur. Potentially conflicting results in the literature on adaptive control of saccadic eye movements are argued to be attributable to the extent to which different task versions elicit goal neglect. The results suggest an increased susceptibility to goal neglect of high-functioning older adults (Experiment 1) and of first-episode schizophrenia patients (Experiment 2), but not of patients with obsessive-compulsive disorder (Experiment 3). However, the degree to which such differences in susceptibility become manifest in task performance, is shown to be strongly influenced by manipulations of the relative saliency of task requirements. Theoretical and methodological implications for the study of executive function are discussed. (C) 2004 Elsevier Inc. All rights reserved.

The primary purpose of the study was to identify event-based prospective-memory tasks that provide sensitive and reliable tools for assessing effects of normal aging in prospective-memory performance. Four prospective-memory tasks were selected from the literature or were newly developed, with the tasks differing on various dimensions that, for theoretical reasons or based on previous evidence. might determine task sensitivity to age effects on prospective-memory performance: perceptual saliency of prospective target events, frequency of occurrence of prospective target events. complexity of prospective-memory instructions. and provision of feedback after prospective-memory errors. Two of the four tasks yielded large and robust age effects on prospective-memory performance. Correlational analyses suggested that these age effects on prospective-memory performance were mediated. at least in part, by a reduced ability of older adults to maintain prospective intentions in a highly activated state and not by age effects on basic mental speed alone. (C) 2002 Elsevier Science (USA).

Interference effects on task performance in conflict situations might reflect real limitations in inhibitory capabilities or failures to fully or consistently utilize such capabilities in executive control of task performance. We propose that useful clues regarding the actual cause of interference effects may be obtained from examination of their robustness within and between experimental conditions. We illustrate this approach for two major types of interference effects that have commonly been attributed to fundamental inhibitory limitations: Stroop-type interference and residual switch costs. We present results that indicate that these effects may not be unavoidable consequences of fundamental inhibitory limitations but may stem from goal neglect, i.e., failures to fully or effectively deploy inhibitory capabilities. These results indicate that, in addition to mean performance levels, variability of task performance may provide a valuable source of evidence regarding the actual cause of performance limitations or deficits in conflict situations. (C) 1999 Elsevier Science B.V. All rights reserved. PsycINFO classification: 2300; 2346; 2360.

A passive Brain Computer Interface (BCI) is a system that responds to the spontaneously produced brain activity of its user and could be used to develop interactive task support. A human-machine system that could benefit from brain-based task support is the driver-car interaction system. To investigate the feasibility of such a system to detect changes in visuomotor workload, 34 drivers were exposed to several levels of driving demand in a driving simulator. Driving demand was manipulated by varying driving speed and by asking the drivers to comply to individually set lane keeping performance targets. Differences in the individual driver’s workload levels were classified by applying the Common Spatial Pattern (CSP) and Fisher’s linear discriminant analysis to frequency filtered electroencephalogram (EEG) data during an off line classification study. Severalfrequency ranges, EEG cap configurations, and condition pairs were explored. It was found that classifications were most accurate when based on high frequencies, larger electrode sets, and the frontal electrodes. Depending on these factors, classification accuracies across participants reached about 95% on average. The association between high accuracies and high frequencies suggests that part of the underlying information did not originate directly from neuronal activity. Nonetheless, average classification accuracies up to 75–80% were obtained from the lower EEG ranges that are likely to reflect neuronalactivity. For a system designer, this implies that a passive BCI system may use several frequency ranges for workload classifications.

Three experiments were conducted to investigate why effects of stimulus-response compatibility (SRC) disappear when the mapping rule is varied randomly and provided only briefly before the imperative stimulus arrives. Three alternative explanations were tested by manipulating automatic response priming, relative probabilities of the mappings, and degree of interference or crosstalk between the mappings. The results indicate that the reduction of SRC effects reflects an active initial suppression of the compatible mapping rule. This suppression appears to be necessary in order to prevent the compatible rule from producing detrimental interference when the incompatible rule is called for instead. These results demonstrate the important role of strategical factors in regulating performance in dynamic task settings.

Finding appropriate measures to trigger machine changes remains a huge challenge in the field of adaptive automation. Trigger candidates include ECG measures and EEG frequencies, which have been linked to various mental states. The aim of such a system would be to avoid both underload and overload situations; which may both be viewed as a predictor of unsafe driving. When driving, task demands and mental effort investment may be regulated by changing driving speed. This could be handled by a biocybernetic system monitoring mental effort investments. To explore which EEG frequencies and locations are most promising to serve as input for such a system, an experiment was conducted (n=34) in which participants were exposed to a range of driving speeds, relative to the driver’s preferred speeds in a rural environment. To increase lateral demand even further, participants were required to stay below several target levels of swerving behavior (standard deviation of the lateral position). These targets were set, relative to the participants normal swerving behaviour. It will be discussed to what extent an EEG based adaptive cruise control is feasible.

The speed-accuracy decomposition technique was developed by Meyer, Irwin, Osman, and Kounios (1988) to examine the time course of information processing. The technique allows for the estimation of the accuracy of guesses that are induced by the presentation of a response signal on a proportion of trials. Estimated guessing accuracy has been found to be above chance and to increase as time of guessing increases, suggesting that guesses are based on partial information that has accumulated prior to a response decision (sophisticated guesses). In this paper, a different interpretation of these data is presented. Results suggest that response signals may enhance the speed of regular processes, thereby violating the temporal-independence assumption that underlies the decomposition technique. As shown by Monte Carlo simulations, such facilitating effects of response signals can explain the results from the decomposition technique at least in part and possibly in full, even when guesses are actually at chance accuracy (pure guesses). The pure-guess model was supported by the results from an experiment designed to test between the alternative interpretations. These results point to the need for great caution in the attempt to infer the time course of information processing from guessing accuracies as estimated by the speed-accuracy decomposition technique.

Three experiments were conducted with 10 grapheme–colour synaesthetes and 10 matched controls to investigate (a) whether awareness of the inducer grapheme is necessary for synaesthetic colour induction and (b) whether grapheme–colour synaesthesia may be bidirectional in the sense that not only do graphemes induce colours, but that colours influence the processing of graphemes. Using attentional blink and Stroop paradigms with digit targets, we found that some synaesthetes did report “seeing” synaesthetic colours even when they were not able to report the inducing digit. Moreover, congruency effects (effects of matching the colour of digit presentation with the synaesthetic colour associated with that digit) suggested that grapheme–colour synaesthesia can be bidirectional, at least for some synaesthetes.

Changes in coherence with aging during cognitive tasks have, until now, not been investigated. However, several fMRI and positron emission tomography studies of cognitive tasks have found increased bilateral activity in elderly subjects. Changes in coherence with aging during a cognitive task were investigated to see if EEG coherence was present in older adults. An auditory oddball task, which is a widely used test for cognitive function, was used. Eleven young adults (27.8 +/- 4.8 years, six females) and 10 older adults (61.3 +/- 4.6 years, six females) were studied, and both interhemispheric and long- and short-range intrahemispheric coherence were considered. Higher interhemispheric coherence was found in the older subjects in the delta band. Short intrahemispheric coherence was also increased in the theta, delta, and alpha bands. Higher coherence, although not significantly different, was also found for all other coherence types and bands, except for long intrahemispheric coherence in the low gamma band. The results presented here provide the first evidence that aging is associated with increased EEG coherence during a relatively easy cognitive task.

A clenched fist is a gesture often seen both within and outside sports that seems to communicate success or to function in self-encouragement or the encouragement of others. This "encouragement gesture" involves the contraction of forearm flexors, similar to the grasping action that is part of acquisitive approach actions. This gesture may be part of a physiological feedback mechanism that functions to increase or sustain levels of approach in challenging situations by signaling the sufficiency of resources (muscle strength). Here we show that for pleasant but not unpleasant words, subjects were faster in categorizing words while contracting their forearm flexors rather than their forearm tensors. This effect dissipated during the first minute of performance, which may reflect habituation of interoceptive feedback. The data further suggest that the effect is larger when experimenter and subject are of opposite sexes. The facilitated responding to pleasant stimuli suggests that contraction of the forearm flexors promotes approach.

The task-switching paradigm provides an opportunity to study whether oscillatory relations in neuronal activity are involved in switching between and maintaining task sets. The EEG of subjects performing an alternating runs [Rogers, R.D., Monsell, S., 1995. Costs of a predictable switch between simple cognitive tasks. Journal of Experimental Psychology: General 124, 207-231] task-switching task was analyzed using event-related potentials, the lateralized readiness potential, instantaneous amplitude and the phase-locking value [Lachaux, J.P., Rodriguez, E., Martinirie, J., Varela, F.J., 1999. Measuring phase synchrony in brain signals. Human Brain Mapping 8, 194-208]. The two tasks differed in the relevant modality (visual versus auditory) and the hand with which responses were to be given. The mixture model [de Jong, R., 2000. An intention driven account of residual switch costs. In: Monsell, S., Driver, J. (Eds.), Attention and Performance XVII: Cognitive Control. MIT Press, Cambridge] was used to assign pre-stimulus switch probabilities to switch trials based on reaction time; these probabilities were used to create a fast-slow distinction between trials on both switch and hold trials. Results showed both time- and time-frequency-domain effects, during the intervals preceding stimuli, of switching versus maintenance, response speed of the upcoming stimulus, and response hand. Of potential importance for task-switching theory were interactions between reaction time by switch-hold trial type that were found for a frontal slow negative potential and the lateralized readiness potential during the response-stimulus interval, indicating that effective preparation for switch trials involves different anticipatory activity than for hold trials. Theta-band oscillatory activity during the pre-stimulus period was found to be higher when subsequent reaction times were shorter, but this response speed effect did not interact with trial type. The response hand of the upcoming task was associated with lateralization of pre-stimulus mu- and beta-band amplitude and, specifically for switch trials, beta-band phase locking. (c) 2005 Elsevier B.V. All rights reserved.

According to the goal-neglect hypothesis of age-related decrements in cognitive control advocated in this paper, such decrements can be usefully and parsimoniously attributed to a reduced capacity for goal selection and goal maintenance in working memory. A selective review of research findings on age-related differences in exogenous and endogenous control of visual attention and eye movements and on performance in the task-switching paradigm serves to illustrate and clarify this hypothesis. The relative merits and scope of the hypothesis are examined within a broader theoretical perspective on the organisation of the domain of executive functions.

The effects of mental fatigue on planning and preparation for future actions were examined, using a task switching paradigm. Fatigue was induced by “time on task,” with subjects performing a switch task continuously for 2 hr. Subjects had to alternate between tasks on every second trial, so that a new task set was required on every second trial. Manipulations of response–stimulus intervals (RSIs) were used to examine whether subjects prepared themselves for the task change. Behavioral measurements, event-related potentials (ERPs), and mood questionnaires were used to assess the effects of mental fatigue. Reaction times (RTs) were faster on trials in which no change in task set was required in comparison with switch trials, requiring a new task set. Long RSIs were used efficiently to prepare for the processing of subsequent stimuli. With increasing mental fatigue, preparation processes seemed to become less adequate and the number of errors increased. A clear poststimulus parietal negativity was observed on repetition trials, which reduced with time on task. This attention-related component was less pronounced in switch trials; instead, ERPs elicited in switch trials showed a clear frontal negativity. This negativity was also diminished by time on task. ERP differences between repetition and switch trials became smaller with increasing time on task.

Several studies are described that explored compatibility effects in dynamic task settings that require flexible and adaptive reactions to sudden and unpredictable changes in perceptual inputs or task requirements. In some cases, dynamic task settings gave rise to emergent organizational demands that caused performance of individual tasks, and manifestations of compatibility, to deviate markedly from that in static single-task settings. In most cases, however, theoretical notions developed previously to account for compatibility effects in static single-task and dual-task settings, also provided a satisfactory account of such effects in dynamic settings. A special status for ideomotor compatibility was highlighted by the fact that only this type of compatibility enabled subjects to react rapidly and efficiently to sudden changes in perceptual input and to make effective use, while being engaged in another task, of instructions regarding an upcoming task.

How is an aiming movement toward a visual target amended when the target suddenly steps to a new position just before or after the movement has started? Three hypotheses are examined: (1) the initial movement needs to be actively terminated before the new movement can be planned and executed, (2) substitution of the initial target position code results, after a normal RT, in the simultaneous termination of the initial movement and initiation of the movement to the new target position, or (3) a second movement from the initial to the second target is initiated after a normal RT, and superimposed on the ongoing movement toward the initial target. The substitution hypothesis assumes a highly continuous and parallel mode of operation of the perceptual-motor system, whereas the other hypotheses assume a distinctly discrete mode of operation. Detailed analyses of double-step movement trajectories clearly favored the substitution hypothesis. These results are discussed with reference to current views on motor control, overlapping-task performance, and the discrete-continuous issue. It is argued that the nature of the perception-action interface depends on the ideomotor compatibility of the task. Perceptual and motor processes operate in a highly continuous and parallel fashion in ideomotor compatible tasks, whereas the interposition of a limited-capacity response selection mechanism results in a discrete and intermittent mode of communication between these processes in non-ideomotor compatible tasks.

We examined how performance of two overlapping discrete tasks is organized and controlled. Experiment 1 showed that when stimuli were presented in an unexpected order, expectations rather than actual presentation order determined the order in which the two stimuli were processed. In Experiment 2, when task order was unpredictable, performance was facilitated when task order was repeated on consecutive trials. In Experiment 3, performance of the second but not the first task benefited greatly when task order was held constant as compared to regularly alternated between trials; such effects were especially pronounced at short intertrial intervals. These results suggest that sequential performance of overlapping tasks is scheduled in advance and is regulated by initially allocating the central processing channel to one task and subsequently switching this channel to the other task.

Distributional analyses and event-related brain potential were used to show that effects of irrelevant spatial stimulus-response correspondence consist of 2 qualitatively different automatic components that can be distinguished on the basis of their dependencies on relative response speed and on computational requirements of the primary task. One component reflects priming of the spatially corresponding response by an abrupt stimulus onset that does not depend on the nature of the primary task. This unconditional component exhibits a biphasic pattern, with initial facilitation later turning into inhibition, analogous to that found for spatial cuing in visual detection tasks. The 2nd component reflects automatic generalization of task-defined transformations of relevant stimulus information to spatial codes; this conditional component does not depend on relative response speed. Possible connectionist implementations of the conditional mechanism are discussed.

Control processes underlying response inhibition were examined. Six Ss performed a visual choice reaction task and were occasionally presented with a tone that told them to withhold the response. Reaction time results were in agreement with a model that assumes a race between response activation and response inhibition processes. Event-related brain potentials, electromyogram, and continuous response measures showed that responses could be interrupted at any time. Evidence was obtained for two inhibitory mechanisms: inhibition of central activation processes and inhibition of transmission of motor commands from central to peripheral structures. Results have implications for the distinction between controlled and ballistic processes.

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.