Activation of the supplementary motor area and of attentional networks during temporal processing.

This paper first provides a survey of the expanding brain imaging literature in the field of time processing, showing that particular task features (discrete vs rhythmic, perceptual vs motor) do not significantly affect the basic pattern of activation observed. Next, positron emission tomography (PET) data obtained in a timing task (temporal reproduction) with two distinct duration ranges (2.2--3.2 and 9--13 s) are reported. The stimuli consisted of vibrations applied to the subject's right middle finger. When the vibration ended, the subject estimated an interval identical to its length before pressing a response button. The control task used cued responses with comparable intervals and stimuli. The pattern of activation obtained in the timing task as compared to control mainly included areas having attentional functions (the right dorsolateral prefrontal, inferior parietal, and anterior cingulate cortices), and the supplementary motor area (SMA). No significant difference was seen as a function of the duration range. It is argued, firstly, that involvement of the attentional areas derives from specific relations between attention and the temporal accumulator, as described by dominant timing models; and, secondly, that the SMA, or more probably one of its subregions, subserves time processing.

The supplementary motor area in motor and sensory timing: evidence from slow brain potential changes.

The present study investigated the processing of durations on the order of seconds with slow cortical potential changes. The question is whether trial-to-trial fluctuations in temporal productions or judgments correspond to variations in the amplitude of surface Laplacians computed over particular scalp regions. Topographical analyses were done using the source derivation method. Subjects performed three successive tasks: (1) time production, in which they produced a 2.5-s interval separated by two brief trigger presses; (2) time discrimination, in which they detected small differences in intervals delimited by two brief clicks in comparison with a memorized standard interval: and (3) intensity discrimination (control task, devoid of time judgments), in which they detected small differences between the intensity of clicks, in comparison with standard clicks initially memorized. In order to focus on subjective differences, in the two discrimination tasks most comparison stimuli were identical to the standard, without the subjects being aware of it. At FCz, reflecting activity from the mesial frontocentral cortex that mainly includes the supplementary motor area (SMA), larger negativities were found during the longer target intervals, whether these were produced (task 1) or judged so (task 2). Those performance-dependent trends were restricted to the target intervals of the temporal tasks; they appeared neither during the 2 s preceding the target, nor during the control task. The data therefore suggest that the SMA subserves important functions in timing both sensory and motor tasks. We propose that the SMA either provides the "pulse accumulation" process commonly postulated in models of time processing or that it receives output from this process through striatal efferent pathways.

Multiple approaches to investigate the existence of an internal clock using attentional resources.

The attentional model of time estimation assumes that specific mechanisms are involved when subjects explicitly process temporal information. Temporal judgments would depend on the amount of attentional resources allocated to a temporal processor (also called timer). The present paper provides some evidence in favor of the existence of such a processor. The first part shows the importance of attention for an efficient functioning of the timer, based on a cumulative mechanism. The second part is centered on the slow brain potential changes recorded over the scalp when subjects focus their attention on the temporal parameters of a task. The main result is the existence of a relationship between the amplitude of the brain waves and the temporal performances.

Attention and timing: dual-task performance in pigeons.

Pigeons were exposed to an analog of a 'dual-task' procedure used to test attentional models of timing in humans. After separate training on an auditory duration discrimination and on a variable ratio (VR) schedule, VR episodes lasting for 5 s were superimposed on the stimuli to be timed, either early (E) or late (L) during the trial. Trials with VR yielded underestimation of the target durations (increased % of 'short' choices), relative to trials without VR, and this effect was stronger under the L than under the E condition. Data were similar to those collected with humans and support attentional models of timing according to which the simultaneous non-timing task uses processing resources which are diverted from the timing mechanisms.

Sensory effects on judgments of short time-intervals.

Two experiments were conducted to test the effect of nontemporal factors on duration discrimination. In Exp. 1, a forced-choice adaptive procedure with a standard duration of 400 or 800 ms was employed. It was shown that, for both auditory and visual modes, the discrimination is better with empty intervals (a silent period between two brief signals) than with filled intervals (a continuous signal), but only with shorter durations. In a second experiment, where intervals of the same duration range were employed but were presented with a single-stimulus method, discrimination was better with empty than with filled intervals, and this effect applied to both ranges of duration and both sensory modes. In both experiments, discrimination was better in the auditory than in the visual mode. These data are discussed in the context of current models of timing mechanisms.

The basic pattern of activation in motor and sensory temporal tasks: positron emission tomography data.

Positron emission tomography (PET) data were obtained from subjects performing a synchronization task (target duration 2700 ms). A conjunction analysis was run to identify areas prominently activated both in this task and in a temporal generalization task (target duration 700 ms) used previously. The common pattern of activation included the right prefrontal, inferior parietal and anterior cingulate cortex, the left putamen and the left cerebellar hemisphere. These areas are assumed to play a major role in time processing, in relation to attention and memory mechanisms.

Effects of attention manipulation on judgments of duration and of intensity in the visual modality.

The "attentional model" of time estimation assumes that temporal judgments depend on the amount of attention allocated to the temporal processor (the timer). One of the main predictions of this model is that an interval will be judged shorter when attention is not allocated to the temporal parameters of the task. Previous studies combining temporal and nontemporal tasks (dual-task method) have suggested that the time spent processing the target duration might be a key factor. The less time devoted by the subject to the temporal task, the shorter the judged duration. In the two experiments presented here, subjects were asked to judge both the duration of a visual stimulus and an increment in intensity occurring at any time during this stimulus. In the second experiment, trials without intensity increments were added. The main result is that the judged duration was shorter when the increment occurred later in the stimulus or did not occur. In those cases, subjects had been expecting increment occurrence during most part of the stimulus and thus had focused for a shorter time on stimulus duration. We propose that attention shifts related to expectancy and to detection of the increment reduce subjective duration.

The "short-long" reaction time effect in duration programming.

The programming processes concerned with response duration were studied in a precueing and in a priming reaction time (RT) paradigm. Participants had to produce a motor response of a specified duration as soon as possible after a response signal (RS) preceded by a warning signal (WS), which could deliver information on 2 response parameters (duration and effector). In Experiment I (precueing; N = 12), 3 effectors (the right hand, the left hand, or the knees) and 3 durations (.7, 2.5, or 5.5 s) were contrasted. Two responses differing in their biomechanical features were required in 2 blocks of trials: Subjects had to accurately time the duration of either a sustained button press or an interval between 2 brief presses. The RT patterns revealed a short-long effect: Shorter RTs were produced before the short duration than before the longer, provided that the duration was not precued. This short-long effect occurred whatever type of response and effector were involved. Two conclusions were reached. First, response duration was included in the motor program elaborated before execution, whatever the biomechanical features of the response; and, second, the program for the short duration was activated on all trials and was used as a basis for programming longer durations when needed. These conclusions were tested in Experiment 2 (priming; N = 12), in which a small proportion of invalid trials concerning duration was provided. Thus, the duration required by the RS differed from that primed by the WS. Two durations (.7 or 2.5 s) and 2 effectors (the index or the middle finger) were involved. In the invalid trials, the responses of short and long durations did not yield any RT differences, thus confirming the particular status of the short duration. This suggests that deprogramming operations (which lengthen the RT) are needed after a RS to produce short response durations but not after a RS to produce long response durations in the invalid trials.

Can the level of prefrontal activity provide an index of performance in humans?

The experiment reported here was aimed at determining whether the level of brain activity can be used as an index of subjects' performance on a temporal task. The discrimination of durations constituted the task. An array of four A's appeared on a screen, and subjects had to decide whether the letters remained on the screen for a short or a long duration as learned in a practice phase. This task allowed us to compare the level of brain activity obtained in correct and incorrect responses. The current density measures recorded over prefrontal areas showed that the level of activity obtained with correct responses was lower than those obtained with incorrect responses. This suggests that a good performance could be the result of an economic, but efficient, information-processing mechanism in the brain.

Brain activation induced by estimation of duration: a PET study.

Duration information about a visual stimulus requires processing as do other visual features such as size or intensity. Using positron emission tomography, iterative H215O infusions, and statistical parametric mapping, we investigated the neural correlates of time processing. Nine normal subjects underwent six serial rCBF. Three tasks were studied: (a) A temporal generalization task (D task) in which the subjects had to judge (by pressing one of two keys) whether the duration of the illumination of a green LED was equal to or different from that of a previously presented standard; (b) An intensity generalization task (I task) in which the judgment concerned the intensity of the LED; and (c) A control task (C task) in which the subjects had to press one of the two keys at random in response to LED illumination. A significant increase in rCBF during the D task, compared to that during the C task, was observed in right prefontal cortex, right inferior parietal lobule, anterior cingulate cortex, vermis, and a region corresponding to the left fusiform gyrus. A significant increase in rCBF during the I task, compared to that during the C task, was observed in right prefontal cortex, right inferior parietal lobule, right extrastriate cortex, anterior cingulate cortex, left inferior parietal lobule, vermis, and two symmetrical regions corresponding to the fusiform gyri. No significant activation was observed in the D task when compared to that in the I task. We propose that these cortical maps are best explained by the recruitment of visual attention and memory structures, which play a major role in prospective time judgements as indicated by behavioral studies. The data also suggest that the temporal dimension of a visual stimulus is processed in the same areas as other visual attributes.

Programming the duration of a motor sequence: role of the primary and supplementary motor areas in man.

Event-related potentials were recorded in a reaction time (RT) paradigm, where the duration of a learned interval (either 0.7 s or 2.5 s) delimited by two brief button-presses was to be accurately controlled. A preparatory signal (PS) either did not give or gave prior information concerning the duration of the following response (neutral condition or primed conditions, respectively). In the latter case, the information was either validated (valid condition) or invalidated (invalid condition) by the response signal (RS). When duration was not known in advance (invalid and neutral conditions), RTs were longer before a response of short than long duration. This difference was not found under the valid condition. During the preparatory period (PP), the amplitude of the contingent negative variation (CNV) was larger when the duration was primed than when it was not. A larger CNV appeared when the PS primed a short rather than a long duration. This effect occurred in the early part of the PP over the supplementary motor area (SMA) and in its latest part over the primary motor area (MI). The RT and the electrophysiological pattern were interpreted as revealing the occurrence of programming operations regarding the temporal dimension of the response. The time course of the CNV over the SMA and MI suggested that these two areas were hierarchically organized. Between the RS and the onset of the response, differences probably related to programming effects were still found over MI: the activities were larger under the valid than under the neutral condition. However, no sign of deprogramming (expected in the invalid condition) was observed: similar amplitudes were found under the neutral and invalid conditions. Deprogramming operations seemed to be postponed during response execution where the invalid condition evoked larger activities than the two other conditions over the SMA. Finally, MI but not the SMA yielded a Bereitschaftpotential before the second press ending the response (i.e., during response execution). These results suggest that the duration of a motor response can be a part of the motor program and that the SMA plays a major role in programming processes but not in response execution, contrary to MI.

Controlled attention sharing influences time estimation.

A seminal attentional model of time estimation predicts that subjective duration will be positively correlated to the amount of attention given to temporal processing. This prediction holds under prospective conditions, in which one is forewarned that judgments of time will be asked, in contrast to retrospective conditions, in which such judgments are required after the relevant period without any prior warning. In three experiments, an attention-sharing method was used. Subjects were asked to control the amount of attention that they devoted to one or the other component of a dual-task paradigm. The first experiment involved word categorization and reproduction of duration. The following experiments, based on signal detection theory, required discrimination of both the duration and the intensity of a single stimulus, in the visual (Experiment 2) or the auditory (Experiment 3) modality. The results indicate that when the attention is directly controlled by the subject, the subjective duration shortens as the amount of attention devoted to the temporal task diminishes. The implications of these results for the possible existence of an internal timer are considered.

Production of short timing responses: a comparative study with a deafferented patient.

How far can proprioception contribute to time keeping? To answer this question, a deafferented patient and neurologically normal subjects produced 1- or 5-sec durations in a sustained (continuous finger press) or discrete (two successive finger taps) manner, with and without Knowledge of Results. The findings were that: (1) proprioceptive afferents contribute to timing regulation in motor production of short durations; (2) this role can be rapidly compensated by Knowledge of Results; (3) the proprioceptive contribution is more important for sustained than for discrete performances; (4) stable performances are produced even when KR is withdrawn, suggesting familiarization with KR leads to the establishment of a mnemonic trace.

Programming response duration in a precueing reaction time paradigm.

To determine whether the duration of certain motor activities can be a prespecified dimension of the motor program, we studied the duration of a motor response and the hand to be used, in a precueing paradigm. The response to be produced (a press on a push-button) was either short or long and involved either the right or the left hand. In Experiment 1, 200 and 700 ms (Block 1) or 700 and 2,500 ms (Block 2) were respectively chosen as short and long durations. No RT difference between short and long appeared when response duration was certain. When response duration was uncertain, RTs were longer for long than for short responses. In addition, the RTs that preceded the 700-ms response were longer in Block 1 than in Block 2. These results suggest that response duration can be programmed up to 2,500 ms and that the relative duration of a response in a given range is more relevant for programming mechanisms than its absolute duration. In Experiment 2, uncertainty concerning the response was maintained constant in a similar precueing paradigm, in which only 700-and 2,500-ms response durations were considered. The RTs preceding a long duration were shorter when duration was certain than when neither side nor duration was certain. No RT difference appeared before the short response duration. This seems to confirm that duration can be programmed up to 2,500 ms and also suggests that the program elaborated for the short duration constitutes a common basis for short and long responses: When duration is uncertain, programming a long duration requires just an additional operation to complete the program corresponding to the short duration, which has already been selected by default.

Effect of learning on production of duration in variable motor conditions.

It has been suggested that increasing proprioceptive feedback and ensuring its consistency from trial to trial favours timing accuracy. The progressive acquisition of a timing performance with isometric and anisometric responses was investigated in conditions of 'inconsistent feedback', with two different methods: counting seconds or not. Subjects gripped the handle of a dynamometer during precisely 5 seconds in 4 randomly distributed conditions: 'Weak' or 'Strong' constant force, 'Slow' or 'Rapid' variable force. A first group produced the durations without counting and a second group counted seconds either mentally or aloud. Learning was examined in 4 successive blocks of trials. Average produced durations did not differ as a function of group, but the variability was reduced when subjects counted seconds. In both groups, the constant force conditions induced more accurate responses than the variable force conditions in the first block of trials. 'Slow' and 'Rapid' conditions were respectively associated with overestimation and under-estimation of response duration. These trends diminished progressively with learning. Both groups yielded sequential effects linked to duration and independent of condition. These data suggest that, whether subjects counted or not, learning was not based on condition-specific proprioceptive feedback. It may involve the elaboration of an internal temporal reference common to all conditions.

Visual and auditory event-related potentials elicited by linguistic and non-linguistic incongruities.

To test the hypothesis that violation of overlearned relations between stimuli in a sequence is critical for eliciting the event-related potential (ERP) N400, we recorded scalp ERPs in sequences where interstimulus relations were either overlearned (sentences or famous songs) or not (geometric figures or scale notes): 25% of the sequences ended with an incongruous stimulus. N400 occurred after incongruous words in sentences only. It seems to index the further processing necessary to specify the nature of the mismatch detected between attended and expected stimuli, when complex information is involved. Earlier components also varied as a function of experimental factors.

Contingent negative variation in processes of expectancy, motor preparation and time estimation.

The contingent Negative Variation (CNV) was compared in four paradigms inducing distinct processes. All paradigms comprised empty intervals of 4 sec bounded by two 100 msec stimuli (S1 and S2) or by S1 and the response (a button press). In paradigm ID (Intensity Discrimination), the S1-S2 interval was followed, after another delay, by a choice response depending on the intensity of S2. In paradigm RT (Reaction Time), the S1-S2 interval was followed by a simple reaction time. In paradigm TP (Time Production), the subjects had to produce a response 4 sec after S1. In paradigm TR (Time Reproduction), the duration of the S1-S2 interval was estimated by the subjects and was to be reproduced after S2. Electrodes were placed on Cz, Fz and Pz in 12 human subjects. The largest CNVs were obtained in paradigm TR. Motor preparation before S2 had no effect on CNV amplitude. Discussion focuses upon the relations between CNV, temporal processes and activation.

Temporal threshold and response bias in the discrimination of empty intervals by cats.

Cat's differential duration threshold was investigated by the method of limits in a schedule of discrimination of empty durations. The standard stimulus was 4 sec long throughout the experiment. The comparison stimulus was reduced from 10 to 5 sec by 1 sec steps in successive blocks of 5 sessions. Standard and comparison stimuli, delimited by 50 msec auditory signals, were equiprobably distributed, in a random sequential order of presentation in each trial. After a 2 sec delay, an auditory signal indicated that reinforcement was available upon a response on one of two levers. Weber fractions around .25 were obtained. Strong response bias developed in most cats. Some consequences of the inhibition of responding induced by the procedure were considered.

An early resolution of contingent negative variation (CNV) in the discrimination.

This study investigates slow potential shifts that occur during a time discrimination task in man. Three experimental series were presented. In series A, each trial included a 5 sec standard interval (SI) followed by a 3 sec SI-TI delay and then by a 4.5, 5.0 or 5.5 sec test interval (TI). The subjects had to estimate whether SI and TI were equal or different and responded by pressing a left or a right button after TI. In series B, the response was postponed after a 3 sec pre-response interval (PRI) succeeding to TI. Series C established an easier discrimination: only 5 or 8 sec TIs were randomly presented in each trial and the subject had to Judge whether he had ben given the "short' or "long' interval. The intervals SI and TI, in which the subject had to collect temporal information, yielded a systematic pattern of slow potential shifts: CNV was followed by an early and prolonged resolution of negativity in the second half of the interval. By contrast, SI-TI delay and PRI only yielded a classical CNV. The "CNV-early resolution' complex appears as a typical feature of temporal tasks. Its possible relation with cognitive processes leading to temporal judgements is discussed, whereas the presence of the only CNV is interpreted as aN indice of expectancy.