Abstract
It is debated whether sub-second timing is subserved by a centralized mechanism or by the intrinsic properties of task-related neural activity in specific modalities (Ivry and Schlerf, 2008). By using a temporal adaptation task, we investigated whether adapting to different time intervals conveyed through stimuli in different modalities (i.e., frames of a visual Ternus display, visual blinking discs, or auditory beeps) would affect the subsequent implicit perception of visual timing, i.e., inter-stimulus interval (ISI) between two frames in a Ternus display. The Ternus display can induce two percepts of apparent motion (AM), depending on the ISI between the two frames: “element motion” for short ISIs, in which the endmost disc is seen as moving back and forth while the middle disc at the overlapping or central position remains stationary; “group motion” for longer ISIs, in which both discs appear to move in a manner of lateral displacement as a whole. In Experiment 1, participants adapted to either the typical “element motion” (ISI = 50 ms) or the typical “group motion” (ISI = 200 ms). In Experiments 2 and 3, participants adapted to a time interval of 50 or 200 ms through observing a series of two paired blinking discs at the center of the screen (Experiment 2) or hearing a sequence of two paired beeps (with pitch 1000 Hz). In Experiment 4, participants adapted to sequences of paired beeps with either low pitches (500 Hz) or high pitches (5000 Hz). After adaptation in each trial, participants were presented with a Ternus probe in which the ISI between the two frames was equal to the transitional threshold of the two types of motions, as determined by a pretest. Results showed that adapting to the short time interval in all the situations led to more reports of “group motion” in the subsequent Ternus probes; adapting to the long time interval, however, caused no aftereffect for visual adaptation but significantly more reports of group motion for auditory adaptation. These findings, suggesting amodal representation for sub-second timing across modalities, are interpreted in the framework of temporal pacemaker model.
Highlights
Timing is fundamental for the brain to process dynamically changing stimuli and interact with the environment
Using a temporal adaptation paradigm, we demonstrated that adaptation to the preceding short temporal interval (50 ms) induced significant negative aftereffects on perception of the subsequent visual Ternus apparent motion (AM), irrespective of whether the time interval was conveyed by events in the same modality or in a different modality
Adaptation to the preceding long temporal interval (200 ms) did not lead to unanimous significant aftereffects across the three tasks, the differences between experiments may reflect the differential impacts of temporal attending in the visual and auditory modalities, rather than distinct time interval representations in different modalities for the sub-second range
Summary
Timing is fundamental for the brain to process dynamically changing stimuli and interact with the environment. The traditional view toward sub-second temporal processing assumes that it is achieved by a centralized mechanism, independent of the specific sensory modality that conveys the temporal information. An implement of this idea is the “temporal pacemaker” model (Treisman, 1963; Treisman et al, 1990, 1994; Ivry et al, 2002), which consists of two major components. The first is a temporal oscillator that emits regular pulses at some fundamental frequency These pulses are gated to a second component, a calibration or “gain control” or switch unit that can increase or decrease the frequency. Repetitive stimuli (clicks or flashes) of high temporal frequency may increase the speed of pacemaker, such that more pulses are accumulated in a given time; repetitive stimuli of low temporal frequency may decrease the speed of pacemaker, Frontiers in Integrative Neuroscience www.frontiersin.org
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