Processing demand modulates the effects of spatial attention on the judged duration of a brief stimulus

How does attention influence the judged duration of a brief stimulus? In the four experiments reported here, we show that the effect of spatial attention on duration judgment depends on the processing demand of the concurrent nontemporal task. When participants had to perform a speeded letter discrimination task in addition to duration rating, the judged duration was longer at a cued location than at an uncued location, regardless of whether the cue was exogenous or endogenous. However, when the same stimuli were presented but no concurrent nontemporal task was required, duration was judged to be shorter at the cued location, as compared with the uncued locations. Furthermore, although spatial attention influenced duration judgment, no object-based attentional effects were found. These findings suggest that, although spatial attention plays an important role in the judged duration of a briefly presented stimulus, its effect is mediated by the processing demand of the task.     

Effects of attention manipulation on judgments of duration and of intensity in the visual modality

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.     

Processing demand modulates the effects of spatial attention on the judged duration of a brief stimulus.

How does attention influence the judged duration of a brief stimulus? In the four experiments reported here, we show that the effect of spatial attention on duration judgment depends on the processing demand of the concurrent nontemporal task. When participants had to perform a speeded letter discrimination task in addition to duration rating, the judged duration was longer at a cued location than at an uncued location, regardless of whether the cue was exogenous or endogenous. However, when the same stimuli were presented but no concurrent nontemporal task was required, duration was judged to be shorter at the cued location, as compared with the uncued locations. Furthermore, although spatial attention influenced duration judgment, no object-based attentional effects were found. These findings suggest that, although spatial attention plays an important role in the judged duration of a briefly presented stimulus, its effect is mediated by the processing demand of the task.     

Effects of stimulus familiarity upon judged visual duration

Five experiments investigated the influence of the differences in stimulus familiarity among a dot-matrix letter, word, and nonword upon the relative judged duration of 30-msec flashes. Figure-ground contrast was manipulated by varying the number of dots comprising each display letter. With 30-msec presentations, judgments ranked subjective durations of the displays nonword > word > letter. Differences in judged duration among stimulus forms were greater when both forward and backward masking reduced recognition probability to chance level than when no mask was employed, and discriminations among masked presentations were easier for subjects. Figure-ground contrast influenced apparent duration judgments only as increases in figure-ground contrast contributed to clarity of familiarity differences among displays. The data were interpreted to indicate that differences in stimulus familiarity operate as early in visual processing as do differences in figure-ground contrast, with greater familiarity facilitating an automatic contact between a stimulus and its memory representation and therein reducing experienced duration.     

Duration perception in crossmodally-defined intervals

How humans perform duration judgments with multisensory stimuli is an ongoing debate. Here, we investigated how sub-second duration judgments are achieved by asking participants to compare the duration of a continuous sound to the duration of an empty interval in which onset and offset were marked by signals of different modalities using all combinations of visual, auditory and tactile stimuli. The pattern of perceived durations across five stimulus durations (ranging from 100 ms to 900 ms) follows the Vierordt Law. Furthermore, intervals with a sound as onset (audio-visual, audio-tactile) are perceived longer than intervals with a sound as offset. No modality ordering effect is found for visualtactile intervals. To infer whether a single modality-independent or multiple modality-dependent time-keeping mechanisms exist we tested whether perceived duration follows a summative or a multiplicative distortion pattern by fitting a model to all modality combinations and durations. The results confirm that perceived duration depends on sensory latency (summative distortion). Instead, we did not find evidence for multiplicative distortions. The results of the model and the behavioural data support the concept of a single time-keeping mechanism that allows for judgments of durations marked by multisensory stimuli.     

A constant error in the perception of brief temporal intervals

Ss were presented two stimuli of equal duration separated in time. The parrs of stimuli were vibrotactile, auditory, or visual. The Ss adjusted the time between the two stimuli to be equal to the duration of the first stimulus. The results show that for stimulus durations ranging from 100 to 1,200 msec, Ss set the tune between the two stimuli too long and by a constant amount. For vibrotactfle stimuli, the constant was 596 msec; for auditory stimuli, 657 msec; and for visual stimuli, 436 msec. Changing the intensity of the vibrotactile stimuli did not change the size of the constant error. When Ss were presented two tones with a burst of white noise between the tones and adjusted the duration of the white noise to be equal to the duration of the first tone, the white noise was not adjusted too long by a constant amount. The results suggest that there is a constant error in the perception of unfilled relative to filled temporal intervals.     

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 effect of expectancy of a threatening event on time perception in human adults

Two experiments were conducted to investigate the effect of a threatening stimulus in human adults in a temporal bisection task. In Experiment 1, for two anchor duration conditions (400/800 vs. 800/1600 ms), the participants completed trials in which the probe duration was followed by an aversive stimulus or a nonaversive stimulus. The results showed that the duration was judged longer when the participants expected an aversive rather than a nonaversive stimulus. In Experiment 2, the effect of the temporal localization of the aversive stimulus was also tested, with the aversive stimulus being presented at the beginning or at the end of the probe duration. The results revealed a temporal overestimation in each condition compared to the trials in which no aversive stimulus was presented. Furthermore, the temporal overestimation was greater when the expectation for the forthcoming threatening stimulus was longer. This temporal overestimation is explained in terms of a speeding-up of the neural timing system in response to the increase in the arousal level produced by the expectation of a threatening stimulus.     

The Effect of Nontemporal Information Processing on Time Estimation in Pigeons

Pigeons' ability to time a stimulus while simultaneously engaged in another information-processing task was examined in three experiments using a matching-to-sample procedure. Pigeons were trained to match temporal samples of 2 and 10 s and were tested with durations of 2, 3, 4.5, 6.7, or 10 s while simultaneously processing information from another dimension. Experiment 1 revealed that the psychophysical curve for long judgments taken when pigeons also had to evaluate line orientation was shifted to the right of a control curve taken from trials on which only time had to be judged. In Experiment 2, results from probe duration tests showed that processing the spatial location of a stimulus while attending to duration caused a more general loss of timing ability across the probe durations (shorter durations were judged as longer and longer durations were judged as shorter). In Experiment 3, a distracter light was illuminated on some probe trials to determine how such a perceptual distraction would affect time judgments on the probe trials. Results showed a general loss of timing ability similar to that found in Experiment 2. It is proposed that the data might best be explained by a divided-attention effect rather than by a systematic effect on the timing mechanism.     

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.     

Speed constancy and the perception of distance

The distance-calibration hypothesis states that retinal velocity is scaled by using distance cues, and judged velocity remains unchanged when distance is changed. The relational hypothesis states that judged velocity depends on retinal velocities, and is proportional to judged distance. These hypotheses were compared in three experiments where the movements of the standard stimulus and the comparison stimulus were manipulated by the ratio of the angular velocity of the comparison stimulus to the angular velocity of the standard stimulus. The presentation conditions of the standard stimulus and the comparison stimulus, and the colour cues of the two stimuli were also manipulated in order to change the strength of the cues available to the observers. The results indicate that judged velocities and the relationship of judged distance and velocity depend on the strength of the cues. When cues are strong, the distance-calibration hypothesis adequately explains speed constancy. When cues are weak, judged velocity and the relationship between judged distance and velocity are consistent with the prediction of the relational hypothesis. The perceived speed of a stimulus depends not only on the physical speed of the stimulus but also on non-motion cues, some of which are distance cues involved in depth perception.     

Perceived tachistoscopic duration and early visual processing in preschool children and adults

Two experiments further explored the Avant et al. (1975) finding that stimulus familiarity influences prerecognition processing to generate differences in the apparent duration of tachistoscopic flashes. The first experiment tested for developmental differences in the effects of upright versus 90°, 180°, and 270° rotations of a single letter or number upon the apparent duration of pre- and postmasked 30- and 50-msec flashes with adults and 4- and 5-year-old children. All age groups judged upright presentations to be of briefer duration. These differences in apparent duration were interpreted to index the automaticity of contacts between stimulus inputs and their memory representations. Failure of the children to recognize the letter and number in any orientation indicates that contact between stimulus inputs and memory representations precedes allocation of attention to the presented stimulus. The second experiment explored the influence of spatial structures which are not coded verbally by testing effects of good and poor dot pattern Gestalts on the apparent duration of tachistoscopic flashes. Adults discriminated between apparent durations of good and poor Gestalts but 4- and 5-year-olds did not. Apparent duration differences in the two experiments showed that spatial pattern structure and familiarity with verbal stimuli influence early visual processing in different ways.     

Perception of the duration of auditory and visual stimuli in children and adults

This experiment investigated the effect of modality on temporal discrimination in children aged 5 and 8 years and adults using a bisection task with visual and auditory stimuli ranging from 200 to 800 ms. In the first session, participants were required to compare stimulus durations with standard durations presented in the same modality (within-modality session), and in the second session in different modalities (cross-modal session). Psychophysical functions were orderly in all age groups, with the proportion of long responses (judgement that a duration was more similar to the long than to the short standard) increasing with the stimulus duration, although functions were flatter in the 5-year-olds than in the 8-year-olds and adults. Auditory stimuli were judged to be longer than visual stimuli in all age groups. The statistical results and a theoretical model suggested that this modality effect was due to differences in the pacemaker speed of the internal clock. The 5-year-olds also judged visual stimuli as more variable than auditory ones, indicating that their temporal sensitivity was lower in the visual than in the auditory modality.     

Absolute identification of notes and intervals by musicians

Speech sounds are judged reliably and absolutely, while the judgment of nonspeech stimuli, such as tones, is thought to be unreliable and dependent on contextual cues. Here we demonstrated that the judgment of tonal stimuli may also be reliable and absolute, provided that the subjects are trained musicians. In Experiment 1, musicians with relative pitch identified 21 tonal intervals ranging from unison to major third, and the resulting identification functions were similar to those that have been previously obtained for speech. In Experiment 3, the judgment of intervals by musicians was shown to be free of context effects, since the best subjects gave virtually identical judgments to the same intervals in two stimulus contexts. Similar results were obtained in Experiments 2 and 4 for the judgment of single tones by possessors of absolute pitch. Performance with both notes and intervals by nonmusicians, however, was unreliable and greatly influenced by context. These findings suggest that musicians acquire categories for pitch that are functionally similar to phonemic categories for speech     

Cerebral asymmetry in time perception

Eighteen right-handed male subjects estimated the duration of dot patterns of varying numerosity which were briefly flashed to the left and right visual fields. The mean judged duration of patterns flashed to the left visual field was significantly less than the mean judged duration of patterns flashed to the right visual field. However, the duration of all patterns was underestimated, regardless of visual field. In addition, apparent duration increased linearly when plotted as a function of log duration and increased monotonically when plotted as a function of stimulus numerosity. Overall accuracy was nearly equivalent in both visual fields, but there were interactions between actual durations and visual field and between numerosity and visual field. Thomas and Weaver’s [1975) model for time perception is applied to the data, and it is suggested that the left hemisphere relies on a timer to estimate duration, while the right hemisphere relies on a visual information processor to estimate duration. nt]mis|The author would like to thank A. B. Kristofferson, S. F. Witelson, an anonymous referee, Mary Kay Fortman, and Allen Gouse for their helpful comments. Some of these data were presented at the meeting of the Midwestern Psychological     

Cognitive processing and time perception

When a visual field is presented for 40 or 80 msec and a subject is asked to judge the duration of the stimulus, judged duration is found to be less when the field is blank than when the field contains three letters, but is the same whether the three letters form a word or not. The perceived difference between “filled” and “blank” fields increases when the subject is required to memorize the presented letters. These data are consistent with a theory which assumes,inter alia, that a stimulus is analyzed by a visual information processor and a timer, that attention is shared between these processors, and that temporal judgments are based on the output of both processors.     

The effect of a flashing visual stimulus on the auditory continuity illusion

The effect of a visual stimulus on the auditory continuity illusion was examined. Observers judged whether a tone that was repeatedly alternated with a band-pass noise was continuous or discontinuous. In most observers, a transient visual stimulus that was synchronized with the onset of the noise increased the limit of illusory continuity in terms of maximum noise duration and maximum tone level. The smaller the asynchrony between the noise onset and the visual stimulus onset, the larger the visual effect on this illusion. On the other hand, detection of a tone added to the noise was not enhanced by the visual stimulus. These results cannot be fully explained by the conventional theory that illusory continuity is created by the decomposition of peripheral excitation produced by the occluding sound.     

时距知觉的扭曲:新异刺激效应

时距知觉会受到刺激新异性的影响,新异刺激的呈现时间往往被认为长于等时距重复出现的标准刺激的呈现时间.已有研究在解释这种主观的时距扩张现象时主要涉及三种假设:注意假设、唤醒假设和神经编码效能假设.研究中的变量混淆问题、跨通道效应和时间因素是今后研究中值得思考的几个问题.对于新异刺激效应产生的心理和神经机制,研究者们还存在着较大分歧.进一步探讨其心理和神经机制对理解时距知觉具有重要意义.     

Action, arousal, and subjective time

Saccadic chronostasis refers to the subjective temporal lengthening of the first visual stimulus perceived after an eye movement. It has been quantified using a duration discrimination task. Most models of human duration discrimination hypothesise an internal clock. These models could explain chronostasis as a transient increase in internal clock speed due to arousal following a saccade, leading to temporal overestimation. Two experiments are described which addressed this hypothesis by parametrically varying the duration of the stimuli that are being judged. Changes in internal clock speed predict chronostasis effects proportional to stimulus duration. No evidence for proportionality was found. Two further experiments assessed the appropriateness of the control conditions employed. Results indicated that the chronostasis effect is constant across a wide range of stimulus durations and does not reflect the pattern of visual stimulation experienced during a saccade, suggesting that arousal is not critical. Instead, alternative processes, such as one affecting the onset of timing (i.e., the time of internal clock switch closure) are implicated. Further research is required to select between these alternatives.