Simon Grondin

Timing and time perception: a review of recent behavioral and neuroscience findings and theoretical directions.

The aim of the present review article is to guide the reader through portions of the human time perception, or temporal processing, literature. After distinguishing the main contemporary issues related to time perception, the article focuses on the main findings and explanations that are available in the literature on explicit judgments about temporal intervals. The review emphasizes studies that are concerned with the processing of intervals lasting a few milliseconds to several seconds and covers studies issuing from either a behavioral or a neuroscience approach. It also discusses the question of whether there is an internal clock (pacemaker counter or oscillator device) that is dedicated to temporal processing and reports the main hypotheses regarding the involvement of biological structures in time perception.

From physical time to the first and second moments of psychological time.

After examination of the status of time in experimental psychology and a review of related major texts, 2 opposite approaches are presented in which time is either unified or fragmented. Unified time perception views, usually guided by Webers law, are embodied in various models. After a brief review of old models and a description of the major contemporary models of time perception, views on fragmented time perception are presented as challenges for any unified time view. Fragmentation of psychological time emerges from (a) disruptions of the Weber function, which are caused by the types of interval presentation, by extensive practice, and by counting explicitly or not; and (b) modulations of time sensitivity and perceived duration by attention and interval structures. Webers law is a useful guide for studying psychological time, but it is also reasonable to assume that more than one so-called central timekeeper could contribute to perceiving time.

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.

Duration discrimination of empty and filled intervals marked by auditory and visual signals

Experiments 1 and 2 compared, with a single-stimulus procedure, the discrimination of filled and empty intervals in both auditory and visual modalities. In Experiment 1, in which intervals were about 250 msec, the discrimination was superior with empty intervals in both modalities. In Experiment 2, with intervals lasting about 50 msec, empty intervals showed superior performance with visual signals only. In Experiment 3, for the auditory modality at 250 msec, the discrimination was easier with empty intervals than with filled intervals with both the forced-choice (FC) and the single stimulus (SS) modes of presentation, and the discrimination was easier with the FC than with the SS method. Experiment 4, however, showed that at 50 and 250 msec, with a FC-adaptive procedure, there were no differences between filled and empty intervals in the auditory mode; the differences observed with the visual mode in Experiments 1 and 2 remained significant. Finally, Experiment 5 compared differential thresholds for four marker-type conditions, filled and empty intervals in the auditory and visual modes, for durations ranging from .125 to 4 sec. The results showed (1) that the differential threshold differences among marker types are important for short durations but decrease with longer durations, and (2) that a generalized Weber’s law generally holds for these conditions. The results as a whole are discussed in terms of timing mechanisms.

Judging the relative duration of multimodal short empty time intervals

Three experiments address the cause of the different performance levels-found in time discrimination of empty intervals with durations near 250 msec. Performance differed according to the kind of sensory modality that marked the intervals. With a procedure in which the type of marker was randomized from trial to trial, it was shown that variability of discrimination judgments could not be attributed entirely to the variability of the criterion on which-a judgment was based. Such a randomization slightly affects discrimination but provokes a reorganization related to marker conditions of the probabilities of judging an interval to be short or long. Moreover, it was shown that within intramodal conditions, physical characteristics of markers influence the discrimination performances. To account for the results generated with different marker-type intervals at 250 msec, we propose that two types of processor may be involved in duration discrimination: one is specifically related to a given sensory modality, whereas the other is aspecific and responsible for discrimination of intermodal intervals.

Psychosocial and neurocognitive profiles in depressed patients with major depressive disorder and bipolar disorder

Previous studies have revealed psychosocial and cognitive impairments in patients during depression. The primary aim of this study was to investigate whether patients with major depression (MDD) and bipolar disorder (BD) differ in psychosocial and neurocognitive profiles. A second aim was to examine whether cognitive impairments are homogeneous among depressed patients. Patients with MDD (n=16) and BD (n=14) were enrolled during a major depressive episode. About half of them had comorbidities, including personality, substance use, and anxiety disorders. Information was collected about symptomatology and psychosocial functioning, whereas an exhaustive neuropsychological battery was administered to assess cognition. During a depressive episode, MDD and BD patients had global psychosocial dysfunction, characterized by occupational and relational impairments. A cognitive slowing was also observed, as well as deficits related to alertness, spontaneous flexibility, sustained and divided attention. Moreover, severity of depression and cognitive functions were significantly associated with psychosocial functioning. In the case of severe mood disorders, psychosocial and neurocognitive functioning seem similar among MDD and BD patients during a depressive episode. In addition to an altered daily functioning, the neurocognitive profile was heterogeneous with regard to the nature and extent of cognitive deficits. Executive functions, as well as verbal learning and memory, were preserved better than attentional processes.

Duration discrimination in crossmodal sequences

Four duration-discrimination experiments were carried out to compare crossmodal and unimodal timing conditions. For all experiments, participants were presented with two sequences, each consisting of 1 or 4 time intervals (marked by 2 or 5 signals), and asked to indicate whether the interval(s) of the second sequence was (were) shorter or longer than the interval(s) of the first. Markers in the first and second sequences were, respectively, tones and flashes (experiment 1), flashes and tones (experiment 2), both flashes (experiment 3), and both tones (experiment 4). In all modality conditions, except when using only tones (experiment 4), increasing the number of repetitions of the variable interval reduced duration-discrimination thresholds, independently of whether the fixed interval was presented first or second within the sequence pair. Moreover, judgments about sequence timing were best for tones–tones sequence pairs, worst for flashes–flashes sequence pairs, and intermediate for crossmodal (flashes–tones or tones–flashes) sequences. Finally, presenting a fixed interval in the first sequence resulted in better discrimination than presenting a variable interval in the first sequence. Implications for theories of timing are discussed.

Overloading temporal memory

This study tested the hypothesis that memory is a major source of variance in temporal processing. Participants categorized intervals as short or long. The number of base durations and interval types mixed within blocks of trials varied from 1 session to another. Results revealed that mixing 2 base durations within blocks increased categorization errors, but mixing 2 marker types did not. Results are attributed to the involvement of more than 1 memory representation, which is argued to show the critical role of memory in temporal processing. Because mixing modalities has no such effect, it was argued that modalities share a common representation in memory. Finally, there was no difference in the perceived duration of auditory and visually marked intervals, which is inconsistent with most reports on this effect.

Discriminating time intervals presented in sequences marked by visual signals

This article presents the results of three experiments on the discrimination of time intervals presented in sequences marked by brief visual signals. In Experiment 1A (continuous condition), the participants had to indicate whether, in a series of 2–4 intervals marked by 3–5 visual signals, the last interval was shorter or longer than the previous one(s). In Experiment 1B (discontinuous condition), the participants indicated whether, in a presentation of two series of 1–3 intervals, with each series being marked by 2–4 signals, the intervals of the second sequence were shorter or longer than those of the first. Whenever one, two, or three standard intervals were presented, the difference threshold was as high at 150 msec as it was at 300 msec with the continuous method but increased monotonically from 150 to 900 msec with the discontinuous method. With both methods, the increase was well described by Weber’s law—the Weber fraction was roughly constant�tween 600 and 900 msec (Experiment 2), whereas between 900 and 1,200 msec (Experiment 3), the Weber fraction increased.

Variable foreperiods and temporal discrimination

Temporal judgements are often accounted for by a single-clock hypothesis. The output of such a clock is reported to depend on the allocation of attention. In the present series of experiments, the influence of attention on temporal information processing is investigated by systematic variations of the period preceding brief empty intervals to be judged. Two indicators of timing performance, temporal sensitivity, reflecting discrimination performance, and perceived duration served as dependent variables. Foreperiods ranged from 0.3 to 0.6 s in Experiments 1 to 4. When the foreperiod varied randomly from trial to trial, perceived duration was longer with increasing length of foreperiod (Experiments 1 and 3 with brief auditory markers and Experiment 4 with brief visual markers), an effect that disappeared with no trial-to-trial variations (Experiment 2). Longer foreperiods also enhanced performance on temporal discrimination of auditory empty intervals with a base duration of 100 ms (Experiments 1 and 5), whereas discrimination performance was unaffected for auditory intervals with a base duration of 500 ms (Experiment 3). The variable-foreperiod effect on perceived duration also held when foreperiods ranged from 0.6 to 1.5 s (Experiments 5—7). Findings suggest that foreperiods appear to effectively modulate attention mechanisms necessary for temporal information processing. However, alternative explanations such as assimilation or compatibility effects cannot be totally discarded.