Rate after-effects fail to transfer cross-modally: Evidence for distributed sensory timing mechanisms

Modality-dependent distortion effects of temporal frequency on time perception

Time perception has been known to depend on the temporal frequency of the stimulus. Previously, the effect of temporal frequency modulation was assumed to be monotonically lengthening or shortening. However, this study shows that temporal frequency affects time perception in a non-monotonic and modality-dependent manner. Four experiments investigated the time distortion effects induced by modulation of temporal frequency across auditory and visual modalities. Critically, the temporal frequency was parametrically manipulated across four levels (steady stimulus, 10-, 20-, and 30/40-Hz intermittent auditory/visual stimulus). Experiment 1, 2, and 3 consistently showed that a 10-Hz auditory stimulus was perceived as shorter than a steady auditory stimulus. Meanwhile, as the temporal frequency increased, the perceived duration of the intermittent auditory stimulus was lengthened. A 40-Hz auditory stimulus was perceived as longer than a 10- Hz auditory stimulus, but did not differ significantly from a steady one. Experiment 4 showed that, for the visual modality, a 10-Hz visual stimulus was perceived as longer than a steady stimulus, and the perceived duration was lengthened as temporal frequency increased. This study demonstrated that within the scope of the temporal frequencies examined in this study, there were differential distortion effects observed across sensory modalities.

Audiovisual interaction with rate-varying signals

A task-irrelevant, amplitude-modulating sound influences perception of a size-modulating visual stimulus. To probe the limits of this audiovisual interaction we vary the second temporal derivative of object size and of sound amplitude. In the study's first phase subjects see a visual stimulus size-modulating with f ″ ( x ) > 0, 0, or <0, and judge each one's rate as increasing, constant, or decreasing. Visual stimuli are accompanied by a steady, non-modulated auditory stimulus. The novel combination of multiple stimuli and multi-alternative responses allows subjects' similarity space to be estimated from the stimulus-response confusion matrix. In the study's second phase, rate-varying visual stimuli are presented in concert with auditory stimuli whose second derivative also varied. Subjects identified each visual stimuli as one of the three types, while trying to ignore the accompanying sound. Unlike some previous results with f ″ ( x ) fixed at 0, performance benefits relatively little when visual and auditory stimuli share the same directional change in modulation. However, performance does drop when visual and auditory stimului differ in their directions of rate change. Our task's computational demands may make it particularly vulnerable to the effects of a dynamic task-irrelevant stimulus.

Weighted Integration of Duration Information Across Visual and Auditory Modality Is Influenced by Modality-Specific Attention

We constantly integrate multiple types of information from different sensory modalities. Generally, such integration is influenced by the modality that we attend to. However, for duration perception, it has been shown that when duration information from visual and auditory modalities is integrated, the perceived duration of the visual stimulus leaned toward the duration of the auditory stimulus, irrespective of which modality was attended. In these studies, auditory dominance was assessed using visual and auditory stimuli with different durations whose timing of onset and offset would affect perception. In the present study, we aimed to investigate the effect of attention on duration integration using visual and auditory stimuli of the same duration. Since the duration of a visual flicker and auditory flutter tends to be perceived as longer than and shorter than its physical duration, respectively, we used the 10 Hz visual flicker and auditory flutter with the same onset and offset timings but different perceived durations. The participants were asked to attend either visual, auditory, or both modalities. Contrary to the attention-independent auditory dominance reported in previous studies, we found that the perceived duration of the simultaneous flicker and flutter presentation depended on which modality the participants attended. To further investigate the process of duration integration of the two modalities, we applied Bayesian hierarchical modeling, which enabled us to define a flexible model in which the multisensory duration is represented by the weighted average of each sensory modality. In addition, to examine whether auditory dominance results from the higher reliability of auditory stimuli, we applied another models to consider the stimulus reliability. These behavioral and modeling results suggest the following: (1) the perceived duration of visual and auditory stimuli is influenced by which modality the participants attended to when we control for the confounding effect of onset-offset timing of stimuli, and (2) the increase of the weight by attention affects the duration integration, even when the effect of stimulus reliability is controlled. Our models can be extended to investigate the neural basis and effects of other sensory modalities in duration integration.

The rhythm aftereffect induced by adaptation to the decelerating rhythm

Rhythm perception can be distorted following prolonged exposure to an isochronous rhythm. It has been suggested that this might arise from the neural adaptation of temporal interval selective neurons. However, the rhythm in our daily life is not always isochronous, and the mechanism that rules the anisochronous rhythm is unclear. Here, we used a sensory adaptation paradigm to investigate whether rhythm perception can be affected by adaptation to the anisochronous rhythm. In Experiments 1 and 2, the direction of tempo change (accelerating vs. decelerating) judgment task and the rhythmic isochronism (isochronous vs. anisochronous) judgment task were used to evaluate participants' perception of rhythms, respectively. We found that after adaptation to a decelerating rhythm, participants tended to perceive the subsequent isochronous rhythm as accelerating. In Experiment 3, visual test rhythms followed the auditory adapting rhythm. In this situation, we did not find any adaptation effects on subsequent rhythm perception. Our results suggest that adaptation to the decelerating rhythm can induce a modality-specific rhythm aftereffect, which is consistent with the temporal order contingent duration aftereffect. It implies a unified timing mechanism for duration and rhythm perception.

Evidence for an A-Modal Number Sense: Numerosity Adaptation Generalizes Across Visual, Auditory, and Tactile Stimuli

Humans and other species share a perceptual mechanism dedicated to the representation of approximate quantities that allows to rapidly and reliably estimate the numerosity of a set of objects: an Approximate Number System (ANS). Numerosity perception shows a characteristic shared by all primary visual features: it is susceptible to adaptation. As a consequence of prolonged exposure to a large/small quantity (“adaptor”), the apparent numerosity of a subsequent (“test”) stimulus is distorted yielding a robust under- or over-estimation, respectively. Even if numerosity adaptation has been reported across several sensory modalities (vision, audition, and touch), suggesting the idea of a central and a-modal numerosity processing system, evidence for cross-modal effects are limited to vision and audition, two modalities that are known to preferentially encode sensory stimuli in an external coordinate system. Here we test whether numerosity adaptation for visual and auditory stimuli also distorts the perceived numerosity of tactile stimuli (and vice-versa) despite touch being a modality primarily coded in an internal (body-centered) reference frame. We measured numerosity discrimination of stimuli presented sequentially after adaptation to series of either few (around 2 Hz; low adaptation) or numerous (around 8 Hz; high adaptation) impulses for all possible combinations of visual, auditory, or tactile adapting and test stimuli. In all cases, adapting to few impulses yielded a significant overestimation of the test numerosity with the opposite occurring as a consequence of adaptation to numerous stimuli. The overall magnitude of adaptation was robust (around 30%) and rather similar for all sensory modality combinations. Overall, these findings support the idea of a truly generalized and a-modal mechanism for numerosity representation aimed to process numerical information independently from the sensory modality of the incoming signals.

Auditory Rate Perception Displays a Positive Serial Dependence

We investigated perceived timing in auditory rate perception using a reproduction task. The study aimed to test (a) whether central tendency occurs in rate perception, as shown for interval timing, and (b) whether rate is perceived independently on each trial or shows a serial dependence, as shown for other perceptual attributes. Participants were well able to indicate perceived rate as reproduced and presented rates were linearly related with a slope that approached unity, although tapping significantly overestimated presented rates. While the slopes approached unity, they were significantly less than 1, indicating a central tendency in which reproduced rates tended towards the mean of the presented range. We tested for serial dependency by seeing if current trial rate reproductions depended on the preceding rate. In two conditions, a positive dependence was observed. A third condition in which participants withheld responses on every second trial produced a negative dependency. These results suggest separate components of serial dependence linked to stimulus and response: Withholding responses reveals a negative perceptual effect, whereas making responses adds a stronger positive effect that is postperceptual and makes the combined effect positive. Together, these data show that auditory rate perception exhibits both central tendency and serial dependence effects.

Temporal rate is not a distinct perceptual metric

Sensory adaptation experiments have revealed the existence of 'rate after-effects' - adapting to a relatively fast rate makes an intermediate test rate feel slow, and adapting to a slow rate makes the same moderate test rate feel fast. The present work aims to deconstruct the concept of rate and clarify how exactly the brain processes a regular sequence of sensory signals. We ask whether rate forms a distinct perceptual metric, or whether it is simply the perceptual aggregate of the intervals between its component signals. Subjects were exposed to auditory or visual temporal rates (a 'slow' rate of 1.5 Hz and a 'fast' rate of 6 Hz), before being tested with single unfilled intervals of varying durations. Results show adapting to a given rate strongly influences the perceived duration of a single empty interval. This effect is robust across both interval reproduction and duration discrimination judgments. These findings challenge our understanding of rate perception. Specifically, they suggest that contrary to some previous assertions, the perception of sequence rate is strongly influenced by the perception of the sequence's component duration intervals.

Cross-Modal Conflict Increases With Time-on-Task in a Temporal Discrimination Task

The modality appropriateness hypothesis argues that the auditory modality is preferred over the visual modality in tasks demanding temporal operations; hence, we predicted that responses to visual stimuli would be more sensitive to the detrimental effect of Time-on-Task. We used a bimodal temporal discrimination task. The factors were durational congruency between the modalities and the direction of modality-transmission. Participants needed to decide the duration of the cued stimulus (visual or auditory). The first five blocks of the task lasted about 1.5 h without rest [Time-on-Task (ToT) period]. The participants then had a 12-min break followed by an additional block of trials. Subjective fatigue, reaction time, error rates, and electrocardiographic data were recorded. In the visual modality, we found an enhanced congruency effect as a function of ToT. The cost of attentional shifting was higher in the auditory modality, but remained constant, suggesting that processing of auditory stimuli is robust against the effects of fatigue. Performance did not improve after the break, indicating that the effects of fatigue could not be overcome by taking a brief break. The heart rate variability (HRV) data showed that vagal inhibition increased with ToT, but this increase was not associated with the changes in performance.

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.