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S Grondin

Publications and source records attributed to S Grondin.

12 recordsLinked to original sources
PubMed2001

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 Weber's 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. Weber's 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.

Attention↗
PubMed2001

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--between 600 and 900 msec (Experiment 2), whereas between 900 and 1,200 msec (Experiment 3), the Weber fraction increased.

Adult↗
PubMed1999

Manual laterality and hitting performance in major league baseball.

Asymmetrical hand function was examined in the context of expert sports performance: hitting in professional baseball. An archival study was conducted to examine the batting performance of all Major League Baseball players from 1871 to 1992, focusing on those who batted left (n = 1,059) to neutralize the game asymmetry. Among them, left-handers (n = 421) were more likely to hit with power and to strike out than right-handers (n = 638). One possible account, based on the idea of hand dominance and an analogy to tennis, is that batting left involves a double-handed forehand for left-handers and a weaker and more reliable double-handed backhand for right-handers. The results are also interpretable in the light of Y. Guiard's (1987) kinematic chain model of a between-hands asymmetrical division of labor, which provides a detailed account of why left batting is optimal for left-handers.

Baseball↗
PubMed1998

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.

Adult↗
PubMed1998

Judgments of the duration of visually marked empty time intervals: linking perceived duration and sensitivity.

The capability of subjects to categorize (as short or long) visually marked empty time intervals was investigated in three experiments. Two visual signals, located 18 degrees to the left (L) and to the right (R) of a fixation point in the visual field, established four marking conditions, two unilaterally presented (L-L and R-R) and two bilaterally presented (L-R and R-L). In Experiments 1 and 2, the results show that discrimination is better with unilateral sequences than with bilateral sequences and that the perceived duration is longer with an L-R than with an R-L sequence. In addition, Experiment 2 shows that, in comparison with a condition in which Markers 1 and 2 remain identical for a complete session, varying the markers from trial to trial does not decrease discrimination. Also, Experiment 2 shows that discrimination is better when both visual markers are presented at fovea than it is in the unilateral conditions. Experiment 3 shows that bilateral intervals are perceived as being longer and are better discriminated than are intervals marked by an intermodal sequence (auditory-visual or visual-auditory). The general discussion reports the implications of having different perceived duration and sensitivity levels, in various marker-type conditions, for an internal-clock hypothesis. Some implications of these results for a lateralized-timer hypothesis are also discussed.

Adolescent↗
PubMed1998

The role of endoscopy in the staging and management of lung metastases.

Endoscopic evaluation of the patient with lung metastases takes on many forms depending upon the extent of disease and the intent of treatment, be that curative or palliative. Thorascopy, and occasionally mediastinoscopy, may be helpful in assessing operability in patients with extensive disease on a preoperative computed tomography scan. However, when in doubt, exploration is always indicated in the young, good risk patient. Palliative efforts usually concern airway obstruction and malignant effects. A variety of technologies, including laser, brachytherapy, and endoluminal stents, helps manage symptomatic bronchial or tracheal lesions.

Airway Obstruction↗
PubMed1996

Markers' influence on the duration discrimination of intermodal intervals.

The effects of sensory signal characteristics on the duration discrimination of intermodal intervals was investigated in three experiments. Temporal intervals were marked by either the successive presentation of a visual then auditory signal (VA), or by the successive presentation of an auditory then visual signal (AV). The results indicated that (1) VA intervals are generally easier to discriminate than are AV intervals, but this effect depends on the range of duration studied; (2) AV intervals are perceived as longer than VA intervals for durations ranging from 250 to 750 msec; (3) the intensity of the visual markers for both AV and VA intervals does not affect the discrimination; and (4) the perceived duration of an intermodal interval is influenced by the length of the first and second markers. The results are mainly interpreted in terms of (1) a sensory trace left by visual and auditory signals and (2) the detection of these signals.

Adult↗
PubMed1994

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.

Adult↗
PubMed1993

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.

Acoustic Stimulation↗
PubMed1992

Production of time intervals from segmented and nonsegmented inputs.

One important factor influencing the accuracy of a timing estimate is the counting activity that a human subject may adopt. In the present study, the usefulness of this activity is evaluated with a strategy whereby subjects are presented segmented and nonsegmented intervals, before they start to produce a series of these intervals, using a finger-tapping procedure. The results are mainly analyzed in the light of Killeen and Weiss's (1987) model, which addressed this question of counting. The results revealed that (1) a scalar property gives a better description of the pacemaker activity than does a Poisson process, and (2) an optimal timing performance would be reached with the utilization of subintervals with an approximate value of 400 msec. Finally, the discussion also incorporates an analysis of the variability related to the motor component in a tapping task.

Adolescent↗
PubMed1991

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.

Adolescent↗