Françoise Macar

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.

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.

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

Abstract 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.

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 CNV peak: an index of decision making and temporal memory.

A slow brain potential change, the contingent negative variation (CNV), was recorded in a temporal generalization schedule. The task was to judge the duration of a signal (1.250 to 3.125 s) as being equal or not to that of a 2-s target that had been previously memorized. Two signal modalities, visual and tactile, were contrasted in distinct trial blocks, in order to explore possible localization differences. Significant results were found at CPz, irrespective of signal modality. The CNV that developed during signal presentation peaked around 2 s and then declined when the current signal was longer than the 2-s target, instead of peaking at signal extinction as was the case for shorter signals. Thus, for signals longer than the target, the CNV peak and the following slope change provide a memory trace of the encoded target duration, leading to decision making.

Event-Related Potentials as Indices of Time Processing: A Review

Abstract This review examines ERP data that document the mechanisms and neural bases of time processing in the millisecond-to-minute range. Several types of ERP attest to the existence of timing capacities. Among them, one component of the Contingent Negative Variation (CNV) provides an on-line index of timing. CNV data strengthen the temporal accumulator concept, designed to subtend duration encoding. This conclusion is based on four main results: The positive relationship between temporal estimates and CNV amplitude is an index of the accumulation mechanism; the CNV peak is an index of time-based decision making; the CNV relates to temporal encoding, whereas temporal long-term memory may be linked to shifts of positive polarity; learning effects on CNV amplitude depend on topographic features, thus revealing functional differences among brain regions with respect to timing.

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.

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.

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.

Time processing reflected by EEG surface Laplacians.

We previously described significant relationships between amplitude variations in slow brain potentials and timed between-press intervals (2.5 s). We suggested that these variations are neural traces of timing mechanisms. To determine which time processing stage is concerned, the current study examines whether these variations result from trial-to-trial memory updating controlled by feedback or from memory consolidation. EEG surface Laplacians (SL) were computed from the first trial on, with feedback (condition 1) and after feedback suppression (condition 2). Performance-dependent variations were related to the individual memory traces revealed by condition 2. As in our previous data, they were restricted to a site overlying the supplementary motor area (SMA). The data suggest that the SMA subserves timing functions, involving memory consolidation and cumulative activation processes as described by current models.