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.Whether time perception relies upon specific chronometric mechanisms or is a by-product of information processing is still a matter of controversy. The data collected in the second or minute range have not always provided a consistent picture. However, the distinction made by Hicks, Miller, and Kinsbourne (1976) between prospective and retrospective judgments of time, which has by now been widely adopted (see Block, 1989;Macar, Pouthas, & Friedman, 1992;Zakay, 1989Zakay, , 1993, has tidied up a number of the inconsistencies. Under prospective conditions, subjects are forewarned that they will be requested to estimate the duration of a particular period. Under retrospective conditions, a time judgment is required after the given period, without any prior warning, and the subject's attention is directed toward other paraThe authors are grateful to Monique Chiambretto, Guy Reynard, and Stan Koren for developing the computer programs, Christophe Vallon and Lynn Metthe for their assistance in data collection, Jessica Blanc for her help with the English language, several colleagues from the Laboratory of Cognitive Neurosciences for seminal discussions on

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.

Among the different brain imaging techniques, electroencephalography (EEG) is classically considered as having an excellent temporal resolution, but a poor spatial one. Here, we argue that the actual temporal resolution of conventional (scalp potentials) EEG is overestimated, and that volume conduction, the main cause of the poor spatial resolution of EEG, also distorts the recovered time course of the underlying sources at scalp level, and hence degrades the actual temporal resolution of EEG. While Current Source Density (CSD) estimates, through the Surface Laplacian (SL) computation, are well known to dramatically reduce volume conduction effects and hence improve EEG spatial resolution, its positive impact on EEG temporal resolution is much less recognized. In two simulation studies, we first show how volume conduction and reference electrodes distort the scalp potential time course, and how SL transform provides a much better spatio-temporal description. We then exemplify similar effects on two empirical datasets. We show how the time courses of the scalp potentials mis-estimate the latencies of the relevant brain events and that CSD provides a much richer, and much more accurate, view of the spatio-temporal dynamics of brain activity.

In a time production task, the participants' activation level and attention devoted to time were manipulated respectively by means of click trains delivered at 2 different intensities during the task and by introducing a concurrent reaction time task. Activation level is classically considered to affect the rate of an internal pacemaker, whereas the way attention affects time estimation is a matter of debate. Three models that differ as to the effect of attention were evaluated. Predictions on the interaction pattern between activation and attention were derived for each of the 3 models. When manipulated jointly, these 2 factors proved to be independent, as they had additive effects on the performance. This finding suggests that the activation level affects the pacemaker rate, whereas the attention level affects an accumulation process by directly acting on a switch functioning in an all-or-none fashion.

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.

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in recruiting, evaluating, and testing the patients and to Eliot Hazeltine and Jennifer Mangels for their comments and criticisms.

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