Is there a constant minimum perceptual duration?

It has been suggested in the recent literature that all stimuli briefer than a critical duration have identical perceptual durations. Relevant simultaneity, reaction time, temporal order and duration discrimination data are discussed, and new data are presented. It is concluded that the relationship between the physical duration of a stimulus and its perceptual duration is not yet understood.     

Some aspects of perceptual coding of duration in visual duration discrimination

Data are presented which indicate two major differences between duration discrimination performance and discrimination performance usually observed in other psychophysical tasks. A decrement in duration discrimination performance with increasing temporal delays between the presentation of two successive stimuli was not found, and the usual difference in level of performance between forced-choice and single-stimulus tasks was not observed. The time-order error in duration discrimination is also discussed.     

Psychophysical theories of duration discrimination

There are few quantitative theories of duration discrimination and few established empirical phenomena to guide theorizing. This paper discusses three such theories and several empirical findings. The theories assume that the discrimination is based only upon information extracted from the temporal extent of the stimulus pattern, and experimental evidence is presented that clearly supports this assumption for many stimulus patterns. Recent findings which indicate that duration information is analyzed in certain ways that are fundamentally different from other stimulus dimensions are reviewed, the duration discrimination psychometric function is examined, and the time-order error is discussed. The three theories are compared in terms of their ability to incorporate the empirical data.     

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. Received: 16 October 1997 / Accepted: 30 April 1998     

Duration discrimination of brief light flashes

The data from four experiments indicate that when Os discriminate between light flashes of different durations, for durations for which Bloch’s law has been shown to hold, their discriminations are frequently made on the temporal information available in the flashes rather than on their apparent brightness. A model for duration discrimination which specifies that discriminability depends only on the difference in duration between the two brief flashes, and is independent of their durations, is presented and applied to the data.     

When are semantic targets detected faster than visual or acoustic ones?

Duration-discrimination data from an experiment using empty auditory intervals in a two-alternative forced-choice paradigm are presented. The observed functional relationship between standard deviation of the psychometric density function and stimulus duration is shown to be fit significantly better by a Weber’s law model of duration discrimination than by Creelman’s counter model. Both models fail to predict the rapid rise in the Weber fraction observed for durations longer than about 2 sec. However, the Weber’s law model, based on a generalization of Weber’s law, accurately predicts the initial drop in the Weber fraction for very short durations and the observed constancy of the Weber fraction for durations up to 2 sec.     

Visual masking effects on duration,size, and form discrimination

In duration, size, and form discrimination tasks, a visual noise mask was presented at variable delays after stimulus offset in order to interrupt processing and control the extent of processing time. Previous work (Thomas & Cantor, 1975) had suggested that both perceived duration and perceived nontemporal “information” might be expected to increase as processing time was extended. As predicted, accuracy in the discrimination of size of circles and form of non-sense figures was found to vary directly with stimulus duration (20, 50 msec) and mask delay interval (0, 30, 70, 110 msec). Differences in perceived duration between filled (forms or circles) and unfilled (blank) intervals were found to increase monotonically with increases in the mask delay interval, when non-sense forms, but not circles, were presented. Two hypotheses of visual masking (“integration” and “interruption”) are discussed. Within the context of the “integration” hypothesis, a model is proposed which predicts processing time as a function of stimulus duration, mask delay interval, and the interval between onset of the mask and termination of processing.     

Changing Sensitivity to Duration in Human Scalar Timing: An Experiment, a Review, and Some Possible Explanations

Evidence from a number of studies of human timing, using temporal generalization and bisection tasks, suggests more sensitive behavioural adjustment to presented durations under conditions in which the timing task demands discriminations between more closely spaced stimuli. An experiment using temporal generalization demonstrated this effect, as discrimination between a 600-msec standard duration and non-standard stimuli both shorter and longer than 600 msec was better when non-standard stimuli were more closely spaced around 600 msec. A review showed similar effects in other temporal generalization tasks and in a number of bisection studies, where time discrimination improved as the ratio of the long and short standards on the bisection task decreased. A standard model of human temporal generalization explained the experimental data in terms of a decrease in the response threshold under more difficult conditions, rather than changes in the representation of the standard duration. On the other hand, data from bisection could be modelled by assuming the contrary; that representations of the short and long standards of the task were more precise under the more difficult conditions. Explanations of some of these effects in terms of attention to duration and/or arousal-induced changes in the speed of an internal clock were discussed.     

Temporal and spatial features in detecting one- and two-dimensional constraints in complementary visual displays

Spatial complements of visual displays of one- and two-dimensional Markov spatial constraints were successively presented for discrimination. Although each complement alone was sufficient for discrimination, spatial complements interfere when presented successively in time. Substantial changes in performance are observed for temporal separations as short as 10 msec and for spatial separations as short as 1 min in visual angle. Complete processing appears to take place in the interval between successive displays: thresholds are constant for a constant sum of display duration plus the interfield interval. Implications of complementary interference for a general theory of visual masking are briefly discussed.     

Applicability of the parallel-clock model to duration discrimination

The parallel-clock model assumes that when an observer is presented with two durations in succession, the total subjective duration (corresponding to the sum of first and second durations) and the second duration are each accumulated in a separate sensory register. In dealing with some relation between the two durations, the observer compares the difference between the contents of the two registers with the contents of the second register. With the further assumption that the psychophysical power law is valid for the continuum of time, the model has previously been shown to account well for duration scaling data. After adapting the model in the vein of Thurstone for duration discrimination data, it was tried out on such data gathered by Allan (1977) from 13 observers. With chi-square as the examined statistic, (1) five distributions were compared and the normal one chosen, (2) one categorization model, three choice models, and two linear regression models were compared with the 3-parameter version of the parallel-lock model, which proved superior, and (3) a 4–5-parameter version of the parallel-clock model, assuming a discontinuity in the psychophysical function, was shown to yield an excellent fit in terms of the Kolmogorov-Smirnov statistic.     

Task dependent modulation of exogenous attention: Effects of target duration and intervening events

Inhibition of return (IOR) consists of slower reaction times in response to stimuli appearing at previously attended or inspected locations. The exact mechanisms underlying the effect have not yet been determined. In the present work, we manipulated two variables, target duration and intervening event (fixation cue between cue and target), through which we modulated the IOR effect as a function of task. When the target was presented until response, the presence of an intervening event made the cueing effect more negative in all tasks, although facilitation in the absence of an intervening event was only observed in discrimination and go–no-go tasks. When the target duration was 50 ms, the effect of the intervening event on cueing was also only observed for the discrimination and go–no-go tasks. Target duration had no effect at all in the discrimination task. Possible mechanisms for these modulations (detection cost and spatial selection benefit, both of which are based on cue–target integration processes) are discussed.     

Duration discrimination of filled and empty auditory intervals: Cognitive and perceptual factors

Adult subjects were presented with two auditory stimuli per trial, and their task was to decide which of the two was longer in duration. An adaptive psychophysical procedure was used. In Experiments 1, 2, and 4, the base duration was 50 msec, whereas in Experiment 3, the base duration was 1 sec. In Experiments 1, 2, and 4, it was found that filled intervals (continuous tones) were discriminated more accurately than empty intervals (with onset and offset marked by clicks). It was concluded that this difference was perceptual rather than cognitive in nature, since performance on filled and empty intervals was not affected by increasing cognitive load in a dual-task procedure (Experiment 2) but was affected by backward masking (Experiment 4). In contrast, the results of Experiment 3 showed that duration discrimination of filled auditory intervals of longer duration was cognitively influenced, since performance was impaired by increasing cognitive load. Implications for notions of perceptual processing and timing mechanisms tanderlying differences in duration discrimination with filled and empty intervals are discussed.     

“Counting” serially presented stimuli by human and nonhuman primates and pigeons

Much of Stewart Hulse's career was spent analyzing how animals can extract patterned information from sequences of stimuli. Yet an additional form of information contained in a sequence may be the number of times different elements occurred. Experiments that required numerical discrimination between different stimulus items presented in sequence are analyzed for primates and pigeons. It is shown that a model based on magnitude discrimination can account well for data from human and nonhuman primate experiments. Similar experiments carried out with pigeons showed a strong recency effect not found with primates. The pigeon data are modeled successfully, however, by assuming that representations of events decay as other events are presented.     

Duration discrimination of filled and empty auditory intervals: cognitive and perceptual factors.

Adult subjects were presented with two auditory stimuli per trial, and their task was to decide which of the two was longer in duration. An adaptive psychophysical procedure was used. In Experiments 1, 2, and 4, the base duration was 50 msec, whereas in Experiment 3, the base duration was 1 sec. In Experiments 1, 2, and 4, it was found that filled intervals (continuous tones) were discriminated more accurately than empty intervals (with onset and offset marked by clicks). It was concluded that this difference was perceptual rather than cognitive in nature, since performance on filled and empty intervals was not affected by increasing cognitive load in a dual-task procedure (Experiment 2) but was affected by backward masking (Experiment 4). In contrast, the results of Experiment 3 showed that duration discrimination of filled auditory intervals of longer duration was cognitively influenced, since performance was impaired by increasing cognitive load. Implications for notions of perceptual processing and timing mechanism underlying differences in duration discrimination with filled and empty intervals are discussed.     

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° 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.     

A diffusion model account of response time and accuracy in a brightness discrimination task: fitting real data and failing to fit fake but plausible data

A brightness discrimination experiment was performed to examine how subjects decide whether a patch of pixels is “bright” or “dark,” and stimulus duration, brightness, and speed versus accuracy instructions were manipulated. The diffusion model (Ratcliff, 1978) was fit to the data, and it accounted for all the dependent variables: mean correct and error response times, the shapes of response time distributions for correct and error responses, and accuracy values. Speed-accuracy manipulations affected only boundary separation (response criteria settings) in the model. Drift rate (the rate of accumulation of evidence) in the diffusion model, which represents stimulus quality, increased as a function of stimulus duration and stimulus brightness but asymptoted as stimulus duration increased from 100 to 150 msec. To address the argument that the diffusion model can fit any pattern of data, simulated patterns of plausible data are presented that the model cannot fit.     

A study of the near-miss involving Weber’s law and pure-tone intensity discrimination

A study of pure-tone intensity discrimination is presented in which amplitude changes are detected in 1000 Hz tone bursts 15–20 msec in duration. The masking function (log detectable increment vs log background intensity) is found to have a slope of 9/10 when calculations are carried out via energy measurements. This near-miss to Weber’s law is in agreement with other data reported in the literature. The masking slope proves to be essentially independent of stimulus duration between 15 msec and 1.5 sec. Our stable slope parameter is interpreted as a detectability restriction generated by “mass-flow” phenomena in the auditory channel. These phenomena are thought to be similar to the fluctuations accompanying a noisy or turbulent stream of events. Pure-tone intensity discrimination is then analyzed as a special case of energy detection.     

Antecedents and Consequences of Perceived Personal Gender Discrimination: A Study of Solicitors in Hong Kong

Informed by social identity theory, we developed a model to examine the antecedents and consequences of perceptions of personal gender discrimination. In the model, gender, gender identity, and perceived gender bias against women are considered as salient predictors of perceived personal gender discrimination, and organizational commitment and intentions to leave are considered as the outcome variables. Structural equation modeling (SEM) was used to analyze the data collected from a sample of practicing solicitors in Hong Kong. We found that (a) women perceived more personal gender discrimination and gender bias against women than did men, (b) gender moderated the relationship between perceived gender bias against women and perceived personal gender discrimination, (c) the positive effect of gender bias against women on gender discrimination was more strongly positive for women than for men, and (d) perceived personal gender discrimination affected organizational commitment and intentions to leave. Theoretical and practical implications are discussed.     

Temporal discrimination as a function of marker duration

In a series of three experiments, the effect of marker duration on temporal discrimination was evaluated with empty auditory intervals bounded by markers ranging from 3 to 300 msec or presented as a gap within a continuous tone. As a measure of performance, difference thresholds in relation to a base duration of 50 msec were computed. Performance on temporal discrimination was significantly better with markers ranging from 3 to 150 msec than with markers ranging from 225 to 300 msec or under the gap condition. However, within each range of marker duration (3–150 msec; 225–300 msec or gap) performance did not differ significantly. A fourth experiment provided evidence that the effect of marker duration cannot be explained in terms of marker-induced masking. A good approximation of the relationship between marker duration and temporal discrimination performance in the present experiments is a smooth step function, which can account for 99.3% of the variance of mean discrimination performance. Thus, the findings of the present study point to the conclusion that two different mechanisms are used in the processing of temporal information, depending on the duration of the auditory markers. The tradeoff point for the hypothetical shift from one timing mechanism to the other may be found at a marker duration of approximately 200 msec.     

Effects of practice and signal energy on duration discrimination of brief auditory intervals

In Experiment 1, the proposition that duration discrimination of filled auditory intervals is based on temporal information rather than on energy-dependent cues was tested in 64 naive subjects. The subjects were presented with two auditory stimuli at different levels of intensity within one trial, and had to decide which of the two was longer in duration. An adaptive psychophysical procedure was used. As a measure of performance, difference threshold estimates in relation to a 50-msec standard interval were computed. Duration discrimination showed no effect of energy values, indicating that the subjects’ discrimination was independent of stimulus intensity. The goal of Experiments 2A and 2B was to investigate the effects of practice on duration discrimination which, in addition, may provide an indirect test for the potential use of energy-dependent cues. Effects of practice on duration discrimination of filled (Experiment 2 A) and empty (Experiment 2B) intervals were studied in 6 subjects in each case, over 20 testing sessions. An adaptive psychophysical procedure that was similar to the one used in Experiment 1 was applied. Neither short-term effects of practice based on the first five testing sessions, nor long-term effects of practice based on the means of 4 consecutive weeks, could be demonstrated. The results of the present study suggest that duration discrimination of brief auditory intervals is based on temporal information and not on stimulus energy. Furthermore, implications for the notion of a very basic bio-logical timing mechanism underlying temporal processing of brief auditory intervals in the range of milliseconds are discussed.