Judgments of temporal duration while processing verbal and physiognomic stimuli

Left- and right-handed male college students made verbal estimations of temporal durations during performance of recognition memory for words and faces, and with no concurrent task. Time judgments were shorter with both concurrent memory tasks than in the control condition, but did not differ between the two memory tasks. Also, these results were additive across groups. Considering the differential involvement of the two cerebral hemispheres in processing verbal and physiognomic stimuli, and the lack of an interaction between group (left- vs right- handers) and memory task, it was concluded that the results do not support a lateralization of function hypothesis with respect to judgments of temporal duration.     

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.     

Maintenance of behavior controlling the duration of discriminative stimuli

The maintenance of a response controlling the duration of positive and negative discriminative stimuli in a multiple schedule was examined with respect to the possible consequences of the response: none, escape from the negative stimulus, production of the positive stimulus, and initiation of the reinforcement schedule associated with the latter. The last two seemed to be the major factors in producing and maintaining the response. Escape from the negative stimulus maintained it in most subjects, but only at a much lower level.     

Perceived duration of expected and unexpected stimuli

Three experiments assessed whether perceived stimulus duration depends on whether participants process an expected or an unexpected visual stimulus. Participants compared the duration of a constant standard stimulus with a variable comparison stimulus. Changes in expectancy were induced by presenting one type of comparison more frequently than another type. Experiment 1 used standard durations of 100 and 400 ms, and Experiments 2 and 3 durations of 400 and 800 ms. Stimulus frequency did not affect perceived duration in Experiment 1. In Experiments 2 and 3, however, frequent comparisons were perceived as shorter than infrequent ones, and discrimination performance was better for infrequent comparisons. Overall, this study supports the notion that infrequent stimuli increase the speed of an internal pacemaker.     

The effects of stimulus numerosity,retinal location,and rod contrast on perceived duration of brief visual stimuli

The effects of manipulating three stimulus parameters were determined on a standard perceived duration task using 40- and 70-msec visual stimuli. In Experiment 1, it was found that perceived duration increased with increasing number of target dots but decreased as the area that contained the dots also increased. Experiment 2 examined the effect of varying the retinal location (0, 2, or 4 deg from fovea) of the target dot and found perceived target duration to increase with increasing eccentricity. In Experiment 3, the background luminance for a constant red target was varied so as to alter the scotopic contrast of the target. Perceived duration was minimal for the scotopically matched target and background conditions. The results of all three experiments were discussed in terms of important retinal—and even rod—contributions to tasks of perceived duration.     

Reaction time to the offset of brief auditory stimuli

An earlier investigator has found that the time at which the offset of a stimulus is perceived depends on the time of stimulusonset, rather than on the time of stimulus offset, for stimuli briefer than a critical duration of the order of 100 msec. In an attempt to determine whether this effect extends to reaction time (RT), we have determined RT to the offset of brief noise bursts. RT was found to be essentially constant as a function of stimulus duration. Thus, RT to stimulus offset appears not to be related to the time of perception of offset, as determined in the earlier investigations.     

Equating the brightness of brief visual stimuli of unequal durations

The brightness of brief displays whose durations do not exceed a critical period of integration is known to covary with stimulus duration (Bloch’s law). There are cases in which the interdependence of duration and brightness introduces an unwanted confounding that must be avoided. Three methods for equating the brightness of brief stimuli displayed under computer control are described and evaluated, and an example of the outcome obtained with the most efficient procedure is reported.     

Hemispheric asymmetries for the temporal resolution of brief auditory stimuli

This study investigates a left-hemisphere (LH) advantage for the discrimination of fine temporal events within the auditory modality in 24 normal adults. Brief noise bursts were delivered monaurally to the left or right ears, half of which contained a gap lasting between 2 and 8 msec. Subjects were required to indicate whether or not the noise burst contained a gap. Research within this area has yielded conflicting results. It is possible that variations in gap position or the properties of the noise burst may have contributed to this conflict. The effect of gap position was investigated by systematically varying the position of the gap during half of the trials. White noise bursts were used to avoid the use of spectral cues. Reaction time, response bias, and response error measures revealed a right-ear (and hence LH) advantage for gap detection. Stable gap positions were recognized more accurately than variable gap positions. Gap position had no effect on the observed LH advantage. These results suggest that the auditory properties of noise burst, rather than gap position, play an important role in the discrepancies observed in this area.     

Judgments of synchrony between auditory and moving or still visual stimuli.

The flash-lag effect is a visual illusion wherein intermittently flashed, stationary stimuli seem to trail after a moving visual stimulus despite being flashed synchronously. We tested hypotheses that the flash-lag effect is due to spatial extrapolation, shortened perceptual lags, or accelerated acquisition of moving stimuli, all of which call for an earlier awareness of moving visual stimuli over stationary ones. Participants judged synchrony of a click either to a stationary flash of light or to a series of adjacent flashes that seemingly bounced off or bumped into the edge of the visual display. To be judged synchronous with a stationary flash, audio clicks had to be presented earlier--not later--than clicks that went with events, like a simulated bounce (Experiment 1) or crash (Experiments 2-4), of a moving visual target. Click synchrony to the initial appearance of a moving stimulus was no different than to a flash, but clicks had to be delayed by 30-40 ms to seem synchronous with the final (crash) positions (Experiment 2). The temporal difference was constant over a wide range of motion velocity (Experiment 3). Interrupting the apparent motion by omitting two illumination positions before the last one did not alter subjective synchrony, nor did their occlusion, so the shift in subjective synchrony seems not to be due to brightness contrast (Experiment 4). Click synchrony to the offset of a long duration stationary illumination was also delayed relative to its onset (Experiment 5). Visual stimuli in motion enter awareness no sooner than do stationary flashes, so motion extrapolation, latency difference, and motion acceleration cannot explain the flash-lag effect.     

Directed attention prolongs the perceived duration of a brief stimulus

Stelmach, Herdman, and McNeil (1994) suggested recently that the perceived duration for attended stimuli is shorter than that for unattended ones. In contrast, the attenuation hypothesis (Thomas & Weaver, 1975) suggests the reverse relation between directed attention and perceived duration. We conducted six experiments to test the validity of the two contradictory hypotheses. In all the experiments, attention was directed to one of two possible stimulus sources. Experiments 1 and 2 employed stimulus durations from 70 to 270 msec. A stimulus appeared in either the visual or the auditory modality. Stimuli in the attended modality were rated as longer than stimuli in the unattended modality. Experiment 3 replicated this finding using a different psychophysical procedure. Experiments 4-6 showed that the finding applies not only to stimuli from different sensory modalities but also to stimuli appearing at different locations within the visual field. The results of all six experiments support the assumption that directed attention prolongs the perceived duration of a stimulus.     

Contrast influences perceived duration of brief time intervals

34 participants judged the duration of a 4-sec. interval which was preceded by a contextual interval of 2, 6, 10, or 14 sec. Underestimations of the test interval when the contextual intervals were longer suggested temporal durations are affected by a mechanism of comparing and contrasting analogous to the one producing some visual illusions.     

The subjective duration of audiovisual looming and receding stimuli

Looming visual stimuli (log-increasing in proximal size over time) and auditory stimuli (of increasing sound intensity over time) have been shown to be perceived as longer than receding visual and auditory stimuli (i.e., looming stimuli reversed in time). Here, we investigated whether such asymmetry in subjective duration also occurs for audiovisual looming and receding stimuli, as well as for stationary stimuli (i.e., stimuli that do not change in size and/or intensity over time). Our results showed a great temporal asymmetry in audition but a null asymmetry in vision. In contrast, the asymmetry in audiovision was moderate, suggesting that multisensory percepts arise from the integration of unimodal percepts in a maximum-likelihood fashion.     

An investigation of visual responses to brief stereoscopic stimuli

An analytic model of the temporal properties of visual responses to brief stimuli is described. The model is based on the notion that visual responses persist for some time after the occurrence of brief stimuli. The model is quantified from data on stereopsis obtained with alternating brief monocular presentations of disparate stimuli. The relevance of the analysis for the data of experiments using tachistiscopic techniques is discussed.     

Fragmentation and identifiability of repeatedly presented brief visual stimuli

Ss were given repeated brief presentations of geometric forms and drew what they thought they saw. The stimulus patterns were presented tachistoscopically for as many repetitions as necessary for correct identification. The nature and sequential properties of pattern fragments reported prior to correct identification were examined. The first fragments to be reported were generally straight line elements of the stimulus patterns. With repeated presentations, more features were gradually reported until the complete figure was correctly identified. The pattern of construction appeared similar to patterns of fragmentation found in research on stabilized retinal images, prolonged afterimages, and conditions of steady fixation. Implications of these findings for theories of pattern information processing were discussed.     

Judgments of duration, figure-ground contrast, and size for words and nonwords

Does the word-superiority effect on letter discrimination result in a word-superiority effect on duration judgments? We examined this question in five experiments. In the first four experiments, we have demonstrated that (1) words shown for 32-80 msec were judged as presented longer than non-words shown for the same duration; (2) this word-superiority effect persists if the stimuli are shown for an objective duration of up to 250 msec; and (3) these effects can be extended to judgments of figure-ground contrast and letter size. These findings extend existing data on effects of processing fluency on perceptual judgments. In Experiment 5, we found that duration judgments were higher for words than for pronounceable nonwords, and duration judgments were higher for pronounceable non-words than for nonpronounceable nonwords. We discuss the implications of this finding for the discrepancy-attribution hypothesis.     

Judgments about forces in described interactions between objects

In 4 experiments, participants made judgments about forces exerted and resistances put up by objects involved in described interactions. Two competing hypotheses were tested: (1) that judgments are derived from the same knowledge base that is thought to be the source of perceptual impressions of forces that occur with visual stimuli, and (2) that judgments are generated using simple models or heuristics for deriving force judgments from kinematic information. The results show some similarities with perceptual impression research, particularly that an active object is judged to exert more force on an inactive object than the latter exerts on the former. However, most of the available kinematic information had little or no effect on judgment, supporting the hypothesis that force judgments are generated according to simple rules. Presentation of information about damage to the objects resulted in use of all available kinds of information; this could reflect greater imageability of damage information than kinematic information.     

Contrasting task demands alter the perceived duration of brief time intervals

Four experiments were performed to assess the effects of task differences on duration judgments. Experiments 1 and 2 used the method of reproduction in prospective, within-subjects designs; their results supported previous research on the effects of task difficulty. Both experiments, using tasks that varied along somewhat different dimensions, found that subjects provided reproduction values that varied inversely with task difficulty. That is, while subjects tended to underreproduce across all tasks, the more difficult the task performed during the target interval, the greater the extent of the under-reproduction. Experiments 3 and 4 used a modification of the reproduction method by placing demands upon the subjects during both the target interval and the reproduction phase of each trial; they demonstrated that the greater the degree of contrast between demands made by the task performed during the target interval and those made during reproduction, the less accurate the duration reproduction. The results are discussed in terms of the contextual and resource allocation models of duration estimation.     

The duration of a brief event in the mind's eye.

A new illusion of perceived duration associated with focused spatial attention is reported. Brief flashes in attended locations were perceived to last longer than the same flashes in unattended locations. That illusion was shown to be completely independent of another illusion concerning the perceived onset of a flash, ruling out the possibility that the effect on perceived duration is derivative of a comparison between perceived onset and offset. The illusion also occurred when the event duration was composed of a temporal gap rather than a brief flash, ruling out low-level visible persistence as a basis for the illusion. Taken together, the results point to cortical connections from higher brain centers' both speeding and prolonging the visual signals occurring in lower sensory regions. Those temporal consequences could easily subserve many of the perceptual benefits ascribed to attention for spatial and intensive properties.     

The contribution of visual persistence to the perceived duration of brief targets

Two experiments were conducted to examine the role of sensory persistence on tasks of perceived duration employing very brief visual stimuli. Using a standard temporal judgment task, the first experiment replicated both the “size effect” and “empty-filled” illusion reported by previous investigators. However, entirely comparable results were also found with a probematching task, which theoretically assesses the degree of persistence exhibited by a stimulus. The second experiment examined the effect of target luminance on perceived duration. Consistent with a sensory persistence interpretation, judgments of duration increased with increasing luminance. The results from the two experiments were discussed in terms of varying degrees of retinal persistence produced by different stimuli. This view was contrasted with currently dominant interpretations that postulate changes in perceived duration to reflect different information-processing requirements across stimulus conditions.