Effect of tactile stimulus frequency on time perception: the role of working memory

No evidence for the effect of entrainment's phase on duration reproduction and precision of regular intervals

Perception of time is not always veridical; rather, it is subjected to distortions. One such compelling distortion is that the duration of regularly spaced intervals is often overestimated. One account suggests that excitatory phases of neural entrainment concomitant with such stimuli play a major role. However, assessing the correlation between the power of entrained oscillations and time dilation has yielded inconclusive results. In this study, we evaluated whether phase characteristics of neural oscillations impact time dilation. For this purpose, we entrained 10-Hz oscillations and experimentally manipulated the presentation of flickers so that they were presented either in-phase or out-of-phase relative to the established rhythm. Simultaneous electroencephalography (EEG) recordings confirmed that in-phase and out-of-phase flickers had landed on different inhibitory phases of high-amplitude alpha oscillations. Moreover, to control for confounding factors of expectancy and masking, we created two additional conditions. Results, supplemented by the Bayesian analysis, indicated that the phase of entrained visual alpha oscillation does not differentially affect flicker-induced time dilation. Repeating the same experiment with regularly spaced auditory stimuli replicated the null findings. Moreover, we found a robust enhancement of precision for the reproduction of flickers relative to static stimuli that were partially supported by entrainment models. We discussed our results within the framework of neural oscillations and time-perception models, suggesting that inhibitory cycles of visual alpha may have little relevance to the overestimation of regularly spaced intervals. Moreover, based on our findings, we proposed that temporal oscillators, assumed in entrainment models, may act independently of excitatory phases in the brain's lower level sensory areas.

Synchronising to a frequency while estimating time of vibro-tactile stimuli

It is well known that subjective time perception can be modified by the emotional experience related to a specific event, by pharmaceutical compounds or by sensory stimuli. As for the latter, visual and auditory stimuli have been widely studied compared to tactile ones. Two experiments were conducted using different vibratory frequencies to stimulate participants who were asked to reproduce stimulus duration. Experiment 1 compared differences in reproduced times for 8-s stimuli ranging between 0.5 and 6 Hz in 100 participants who performed a time reproduction task with the stimulus present or absent during the reproduction. The task was done under prospective and retrospective paradigms. Experiment 2 assessed differences in reproduced times by 80 participants under vibrotactile stimulation of two frequencies simultaneously delivered to each hand, frequencies with specific proportions of 0.5 and 0.75 times the standard frequency for two groups of standard frequency (2 or 12 Hz). Reproduced times in Experiment 1 did not show significant differences among frequencies. Significant differences were found for the absence/presence condition, solely, in prospective tasks, where estimations were longer in the absence of the vibrotactile stimulus. Significant differences were found in Experiment 2 for reproduced time by participants between groups of standard frequency. Data analysis suggests the need to improve the understanding of the subjective time perception processes for higher frequencies considering the intensity modulation based on the amplitude and frequency relation. Results open the possibility of designing new protocols in the study of time perception and other cognitive functions.

The effects of odor and body posture on perceived duration

This study reports an examination of the internal clock model, according to which subjective time duration is influenced by attention and arousal state. In a time production task, we examine the hypothesis that an arousing odor and an upright body posture affect perceived duration. The experimental task was performed while participants were exposed to an odor and either sitting upright (arousing condition) or lying down in a relaxing chair (relaxing condition). They were allocated to one of three experimental odor conditions: rosemary (arousing condition), peppermint (relaxing condition), and no odor (control condition). The predicted effects of the odors were not borne out by the results. Self-reported arousal (SRA) and pleasure (PL) states were measured before, during (after each body posture condition) and postexperimentally. Heart rate (HR) and skin conductance were measured before and during the experiment. As expected, odor had an effect on perceived duration. When participants were exposed to rosemary odor, they produced significantly shorter time intervals than in the no odor condition. This effect, however, could not be explained by increased arousal. There was no effect of body posture on perceived duration, even though body posture did induce arousal. The results do not support the proposed arousal mechanism of the internal clock model.

Perceived duration of Visual and Tactile Stimuli Depends on Perceived Speed

IT IS KNOWN THAT THE PERCEIVED DURATION OF VISUAL STIMULI IS STRONGLY INFLUENCED BY SPEED: faster moving stimuli appear to last longer. To test whether this is a general property of sensory systems we asked participants to reproduce the duration of visual and tactile gratings, and visuo-tactile gratings moving at a variable speed (3.5-15 cm/s) for three different durations (400, 600, and 800 ms). For both modalities, the apparent duration of the stimulus increased strongly with stimulus speed, more so for tactile than for visual stimuli. In addition, visual stimuli were perceived to last approximately 200 ms longer than tactile stimuli. The apparent duration of visuo-tactile stimuli lay between the unimodal estimates, as the Bayesian account predicts, but the bimodal precision of the reproduction did not show the theoretical improvement. A cross-modal speed-matching task revealed that visual stimuli were perceived to move faster than tactile stimuli. To test whether the large difference in the perceived duration of visual and tactile stimuli resulted from the difference in their perceived speed, we repeated the time reproduction task with visual and tactile stimuli matched in apparent speed. This reduced, but did not completely eliminate the difference in apparent duration. These results show that for both vision and touch, perceived duration depends on speed, pointing to common strategies of time perception.

Duration Discrimination by Musicians and Nonmusicians

This study investigated the effects of stimulus modality, standard duration, sex, and laterality in duration discrimination by musicians and nonmusicians. Seventeen musicians ( M age = 24.1 yr.) and 22 nonmusicians ( M age = 26.8 yr.) participated. Auditory (1,000 Hz) and tactile (250 Hz) sinusoidal suprathreshold stimuli with varying durations were used. The standard durations tested were 0.5 and 3.0 sec. Participants discriminated comparison stimuli which had durations slightly longer and shorter than the standard durations. Difference limens were found by the method of limits and converted to Weber fractions based on the standard durations. Musicians had lower, i.e., better, Weber fractions than nonmusicians in the auditory modality, but there was no significant difference between musicians and nonmusicians in the tactile modality. Auditory discrimination was better than tactile discrimination. Discrimination improved when the standard duration was increased both for musicians and nonmusicians. These results support previous findings of superior auditory processing by musicians. Significant differences between discrimination in the millisecond and second ranges may be due to a deviation from Weber's law and the discontinuity of timing in different duration ranges reported in the literature.