Shortening of Subjective Visual Intervals Followed by Repetitive Stimulation

Citation: Ono F, Kitazawa S ( Shortening of Subjective Visual Intervals Followed by Repetitive Stimulation Fuminori Ono 0 Shigeru Kitazawa 0 Georges Chapouthier, Universite Pierre et Marie Curie, France 0 1 Research Center of Advanced Science and Technology, The University of Tokyo, Tokyo, Japan, 2 Dynamic Brain Network Laboratory, Graduate School of Frontier Biosciences, Osaka University , Osaka , Japan , 3 Department of Brain Physiology, Graduate School of Medicine, Osaka University , Osaka , Japan Our previous research demonstrated that repetitive tone stimulation shortened the perceived duration of the preceding auditory time interval. In this study, we examined whether repetitive visual stimulation influences the perception of preceding visual time intervals. Results showed that a time interval followed by a high-frequency visual flicker was perceived as shorter than that followed by a low-frequency visual flicker. The perceived duration decreased as the frequency of the visual flicker increased. The visual flicker presented in one hemifield shortened the apparent time interval in the other hemifield. A final experiment showed that repetitive tone stimulation also shortened the perceived duration of preceding visual time intervals. We concluded that visual flicker shortened the perceived duration of preceding visual time intervals in the same way as repetitive auditory stimulation shortened the subjective duration of preceding tones. - Substantial evidence indicates that the subjective experience of time does not exactly match the actual duration of events; rather, perceived durations stretch or contract depending on properties that are ostensibly independent of the elapsed time. For example, accumulated evidence shows that the perception of the duration of a time interval is lengthened by presenting the subject with repetitive tone stimuli [1], [2] or visual flickers [2][4] before the test interval. In fact, the durations of either a rapid series of tones [5][7] or flickering visual stimuli [8] are themselves perceived to be longer than the physical duration. To explain these changes in time perception, researchers have generally hypothesized that there is some kind of internal pacemaker [9] that is accelerated by repetitive stimulation. Acceleration of this pacemaker leads to an increase in pulse counts during a given period, which eventually leads to an increase in subjective duration. It is worth noting that these previous studies explained the effects of repetitive stimulation that was presented before or during a timed test interval. The pacemaker framework is embedded in scalar expectancy theory (SET; [10]), which is one of the most popular contemporary models of time perception. SET proposes that temporal processing consists of three major components namely, a clock process (consisting of a pacemaker and an accumulator), a memory process (consisting of short-term- and reference-memory stores), and a comparator process (which aids decision making). A number of studies have attempted to manipulate the clock component of the model in either animals [11], [12] or humans [1], [3] and have provided evidence for a pacemakeraccumulator clock similar to that proposed by SET. However, much less attention has been paid to the memory and decision-making components of the model. One way to examine these components is to deliver an external perturbation during memory or decision processing and to evaluate its effects on time perception. In our previous study [13], we examined whether repetitive tone stimuli (presented after a time interval) altered the perception of the preceding time interval in a postdictive manner. In the experiment, one trial consisted of reference and test intervals. The intervals were defined by delivering the first tone, followed by a silent period, followed by a second tone. Immediately after a test interval, a rapid series of tones (auditory flutter) was presented. The participants judged whether the test interval was longer than the reference interval. Interestingly, we found that the perceived duration of the preceding test interval was shortened by the occurrence of repetitive tone stimuli that followed the test interval (in what follows, this is referred to as a flutter effect). In addition, we showed that the flutter effect was not due to a framing effect. From our results, we proposed a postdictive evaluation mechanism that depends on the current rate of the internal pacemaker. Suppose, for example, that a person with a pacemaker of 10 pulses/s timed a 1-s interval that was immediately followed by a rapid series of tones. In this scenario, 10 pulses would be stored in his accumulator at the end of the 1-s interval; however, the succeeding series of tones would speed up the internal pacemaker to (for example) 11 pulses/s. We proposed that the stored pulse count (10 pulses) would be normalized by the clock speed (11 pulses/s) immediately after the end of pulse counting, in a postdictive manner. In this case, the perceived duration would be shortened by approximately 10% relative to when the clock speed remained constant (10 pulses/s). In the present study, we examine whether the following repetitive stimulation effect is limited to auditory stimuli or whether it could also occur with visual stimuli. A fundamental question about time perception is whether the mechanisms underlying temporal judgments are universal and centralized in the brain or whether they are modality-specific and distributed [14][16]. Most psychophysical models of time perception have assumed the existence of an internal pacemaker that is common to both vision and audition [9], [17][22]. In contrast, some authors provided evidence that suggests that the timing of brief intervals is modality dependent [14], [23][25]. To examine this question, we presented a flickering visual stimulus after a test interval. If there is no such postdictive mechanism in the visual modality, the visual flicker stimulation should have no effect on subjective duration. If this postdictive mechanism is present in the visual system, the perceived duration of the visual interval should be shortened by the visual flicker. In experiment 1, we examined the effect of a visual flicker that followed a test interval. Methods Observers. Six paid volunteers participated; new participants were recruited for experiments 25. All participants were unaware of the purpose of the experiment, had normal hearing, and had normal (or corrected-to-normal) visual acuity. The procedures were approved by the internal review board of Research Center for Advanced Science and Technology, The University of Tokyo, and written informed consent was obtained from all participants prior to the testing. Apparatus and Stimuli. Participants were seated approximately 60 cm away from a monitor (Iiyama HM204D, 100 Hz) in a dark, quiet room. Experiments were run on a PC/ AT compatible computer using a ViSaGe stimulus generat (...truncated)