How long depends on how fast--perceived flicker dilates subjective duration

Temporal correspondence in perceptual organization: Reciprocal interactions between temporal sensitivity and figure-ground segregation

How do visual representations account for time? Is it the case that they represent time by themselves possessing temporal properties (temporal mirroring) or by atemporal markers/tags (temporal tagging)? This question has been asked for the past 5 decades and more, in neuroscience, philosophy, and psychology. To address this debate, we designed a study to test temporal correspondence. We tested whether a temporal property (flicker frequency) could influence figure-ground segregation, and in turn, reciprocally, whether a figure-ground segregation would alter a temporal property (here, temporal resolution). We manipulated flicker frequency of dots on either side of an ambiguous edge in Experiment 1 and asked participants to indicate the figural region. In Experiment 2, we measured temporal sensitivity using a temporal order judgment (TOJ) task in both figural and ground regions. We showed temporal correspondence by showing specifically that figure-ground segregation depends on flicker frequency differences between two regions in ambiguous displays, where slow-flickering regions are seen as figural (Experiment 1). Reciprocally, in Experiment 2, we showed that participants performed a temporal-order judgment task better when the task had to be performed on a region seen as background compared with the same region seen as a figure. We show how relatively slower flickering regions are seen as figural, and correspondingly, seeing a region as figural is associated with a poorer temporal resolution. Our results collectively allow us to demonstrate a tight temporal correspondence in figure-ground perception, which could be explained using the parvocellular and magnocellular pathways, the two major retino-geniculo-cortical pathways.

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.

An event-termination cue causes perceived time to dilate

The perceived duration of time does not veridically reflect the physical duration but is distorted by various factors, such as the stimulus magnitude or the observer's emotional state. Here, we showed that knowledge about an event's termination time is another significant factor. We often experience time passage differently when we know that an event will terminate soon. To quantify this, we asked 33 university students to report a rotating clock hand's duration with or without a termination cue that indicated the position at which the clock hand disappeared. The results showed that the presence of the termination cue dilated perceived durations, and the dilating effect was larger when the stimulus duration was longer, or the speed of the rotating stimulus was slower. A control experiment with a start-cue excluded the possibility that the cue's mere existence caused the results. Further computational analyses based on the attention theory-of-time perception revealed that the size of dilation is best explained by neither an event's duration nor the distance traveled by the clock hand, but by how long the clock hand spends time near the termination cue. The results imply that an event-termination cue generates a field in which the perceived time dilates.

Distinctive features of experiential time: Duration, speed and event density

William James's use of "time in passing" and "stream of thoughts" may be two sides of the same coin that emerge from the brain segmenting the continuous flow of information into discrete events. Herein, we investigated how the density of events affects two temporal experiences: the felt duration and speed of time. Using a temporal bisection task, participants classified seconds-long videos of naturalistic scenes as short or long (duration), or slow or fast (passage of time). Videos contained a varying number and type of events. We found that a large number of events lengthened subjective duration and accelerated the felt passage of time. Surprisingly, participants were also faster at estimating their felt passage of time compared to duration. The perception of duration scaled with duration and event density, whereas the felt passage of time scaled with the rate of change. Altogether, our results suggest that distinct mechanisms underlie these two experiential times.

The WACDT, a modern vigilance task for network defense

Vigilance decrement refers to a psychophysiological decline in the capacity to sustain attention to monotonous tasks after prolonged periods. A plethora of experimental tasks exist for researchers to study vigilance decrement in classic domains such as driving and air traffic control and baggage security; however, the only cyber vigilance tasks reported in the research literature exist in the possession of the United States Air Force (USAF). Moreover, existent cyber vigilance tasks have not kept up with advances in real-world cyber security and consequently no longer accurately reflect the cognitive load associated with modern network defense. The Western Australian Cyber Defense Task (WACDT) was designed, engineered, and validated. Elements of network defense command-and-control consoles that influence the trajectory of vigilance can be adjusted within the WACDT. These elements included cognitive load, event rate, signal salience and workload transitions. Two forms of the WACDT were tested. In static trials, each element was adjusted to its maximum level of processing difficulty. In dynamic trials, these elements were set to increase from their minimum to their maximum values. Vigilance performance in static trials was shown to improve over time. In contrast, dynamic WACDT trials were characterized by vigilance performance declines. The WACDT provides the civilian human factors research community with an up-to-date and validated vigilance task for network defense accessible to civilian researchers.

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.

The speed and temporal frequency of visual apparent motion modulate auditory duration perception

In the present study, we investigated how the perception of auditory duration could be modulated by a task-irrelevant, concurrent visual apparent motion, induced by visual bars alternating between left and right sides. Moreover, we examined the influence of the speed and temporal frequency of visual apparent motion on the perception of auditory duration. In each trial, the standard visual stimuli (two vertical bars) were presented sequentially, except that visual apparent motion was included in the fourth stimulus. A tone was presented simultaneously with each visual stimulus, while the fourth tone was presented with varied duration. Participants judged whether the fourth tone lasted longer than the other four tones. In Experiment 1, the speed of visual apparent motion (Fast vs. Slow) was manipulated by changing the interval between two bars. The mean point of subjective equality (PSE) in the Slow apparent motion condition was larger than that in the Static condition. Moreover, participants tended to overestimate the duration only in the Static condition, i.e., time dilation effect, which disappeared under apparent motion conditions. In Experiment 2, in addition to speed, we controlled the temporal frequency of apparent motion by manipulating the number of bars, generating four conditions of visual apparent motion (Physical-fast, Perceived-fast, Perceived-slow, vs. Static). The mean PSE was significantly smaller in the Physical-fast condition than in the Static and Perceived-slow conditions. Moreover, we found a time compression effect in both the Perceived-slow and Static conditions but not in the Perceived-fast and Physical-fast conditions. These results suggest that the auditory duration could be modulated by the concurrent, contextual visual apparent motion, and both the speed and temporal frequency of the task-irrelevant visual apparent motion contribute to the bias in perceiving the auditory duration.

Application of rapid invisible frequency tagging for brain computer interfaces

BACKGROUND

Brain-computer interfaces (BCI) based on steady-state visual evoked potentials (SSVEPs/SSVEFs) are among the most commonly used BCI systems. They require participants to covertly attend to visual objects flickering at specified frequencies. The attended location is decoded online by analysing the power of neuronal responses at the flicker frequency.

NEW METHOD

We implemented a novel rapid invisible frequency-tagging technique, utilizing a state-of-the-art projector with refresh rates of up to 1440 Hz. We flickered the luminance of visual objects at 56 and 60 Hz, which was invisible to participants but produced strong neuronal responses measurable with magnetoencephalography (MEG). The direction of covert attention, decoded from frequency-tagging responses, was used to control an online BCI PONG game.

RESULTS

Our results show that seven out of eight participants were able to play the pong game controlled by the frequency-tagging signal, with average accuracies exceeding 60 %. Importantly, participants were able to modulate the power of the frequency-tagging response within a 1-second interval, while only seven occipital sensors were required to reliably decode the neuronal response.

COMPARISON WITH EXISTING METHODS

In contrast to existing SSVEP-based BCI systems, rapid frequency-tagging does not produce a visible flicker. This extends the time-period participants can use it without fatigue, by avoiding distracting visual input. Furthermore, higher frequencies increase the temporal resolution of decoding, resulting in higher communication rates.

CONCLUSION

Using rapid invisible frequency-tagging opens new avenues for fundamental research and practical applications. In combination with novel optically pumped magnetometers (OPMs), it could facilitate the development of high-speed and mobile next-generation BCI systems.

Trial-by-trial predictions of subjective time from human brain activity

Human experience of time exhibits systematic, context-dependent deviations from clock time; for example, time is experienced differently at work than on holiday. Here we test the proposal that differences from clock time in subjective experience of time arise because time estimates are constructed by accumulating the same quantity that guides perception: salient events. Healthy human participants watched naturalistic, silent videos of up to 24 seconds in duration and estimated their duration while fMRI was acquired. We were able to reconstruct trial-by-trial biases in participants’ duration reports, which reflect subjective experience of duration, purely from salient events in their visual cortex BOLD activity. By contrast, salient events in neither of two control regions–auditory and somatosensory cortex–were predictive of duration biases. These results held despite being able to (trivially) predict clock time from all three brain areas. Our results reveal that the information arising during perceptual processing of a dynamic environment provides a sufficient basis for reconstructing human subjective time duration.

Our perception of time isn’t like a clock; it varies depending on other aspects of experience, such as what we see and hear in that moment. Previous studies have shown that differences in simple features, such as an image being larger or smaller, or brighter or dimmer, can change how we perceive time for those experiences. But in everyday life, the properties of these simple features can change frequently, presenting a challenge to understanding real-world time perception based on simple lab experiments. To overcome this problem, we developed a computational model of human time perception based on tracking changes in neural activity across brain regions involved in sensory processing (using non-invasive brain imaging). By measuring changes in brain activity patterns across these regions, our approach accommodates the different and changing feature combinations present in natural scenarios, such as walking on a busy street. Our model reproduces people’s duration reports for natural videos (up to almost half a minute long) and, most importantly, predicts whether a person reports a scene as relatively shorter or longer–the biases in time perception that reflect how natural experience of time deviates from clock time.

Electrophysiological Evidence for a Common Magnitude Representation of Spatiotemporal Information in Working Memory

Spatiotemporal interference has attracted increasing attention because it provides a window for studying the neural representation of magnitude in the brain. We aimed to identify the neural basis of spatiotemporal interference using a Kappa effect task in which two circles were presented in sequence with two time intervals and three space distances. Participants reproduced the time intervals while ignoring the space distance when electroencephalogram signals were recorded synchronously. The behavior results showed that production time increased with time interval and space distance. Offset of the time intervals elicited typical P2 and P3b components. Larger parietal P2 and P3b amplitudes were elicited by the combination of longer time intervals and longer space distances. The parietal P2 and P3b amplitudes were positively correlated with the production time, and the corresponding neural source was located in the parietal cortex. The results suggest that the parietal P2 and P3b index updates a common representation of spatiotemporal information in working memory, which provides electrophysiological evidence for the mechanisms underlying spatiotemporal interferences. Our study supports a theory of magnitude, in which different dimensions can be integrated into a common magnitude representation in a generalized magnitude system that is localized at the parietal cortex.

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.

Effect of glare illusion-induced perceptual brightness on temporal perception

Temporal perception and the ability to precisely ascertain time duration are central to essentially all behaviors. Since stimulus magnitude is assumed to be positively related to the perceived duration from the early days of experimental psychology, most studies so far have assessed this effect by presenting stimuli with relatively different intensities in physical quantity. However, it remains unclear how perceptual magnitude itself directly affects temporal perception. In this study (n = 21, n = 20), we conducted a two‐interval duration‐discrimination task adapting a glare illusion (a visual illusion that enhances perceived brightness without changing physical luminance) to investigate whether the temporal perception is also influenced by perceptual magnitude. Based on the mean difference in the point of subjective equality derived from a psychometric function and pupil diameter, we found that temporal perception is influenced by the illusory brightness of glare stimuli. Interestingly, the perceived duration of the apparently brighter stimuli (glare stimuli; larger pupillary light reflex) was shorter than that of control stimuli (halo stimuli; smaller pupillary light reflex) despite the stimuli remaining physically equiluminant, in contrast with the well‐known "magnitude effect." Furthermore, this temporal modulation did not occur when the physical luminance of the stimuli was manipulated to match the illusory‐induced magnitude. These results indicate that temporal processing depends on the confluence of both external and perceived subjective magnitude and even illusory brightness is sufficient to affect the sense of duration; which may be explained by the internal magnitude decrease of the glare stimuli due to pupillary constriction decreasing the light entering the eye.

Our findings suggest a new viewpoint on the positive relationship between temporal perception and stimulus magnitude, in demonstrating that temporal processing depends on the confluence of both external and perceived internal magnitude. We provide evidence that illusory brightness induced by the glare‐illusion also influences the perceived duration which may be explained by the size of the pupil.

Modulation of Individual Alpha Frequency with tACS shifts Time Perception

Previous studies have linked brain oscillation and timing, with evidence suggesting that alpha oscillations (10 Hz) may serve as a "sample rate" for the visual system. However, direct manipulation of alpha oscillations and time perception has not yet been demonstrated. To test this, we had 18 human subjects perform a time generalization task with visual stimuli. Additionally, we had previously recorded resting-state EEG from each subject and calculated their individual alpha frequency (IAF), estimated as the peak frequency from the mean spectrum over posterior electrodes between 8 and 13 Hz. Participants first learned a standard interval (600 ms) and were then required to judge if a new set of temporal intervals were equal or different compared with that standard. After learning the standard, participants performed this task while receiving occipital transcranial Alternating Current Stimulation (tACS). Crucially, for each subject, tACS was administered at their IAF or at off-peak alpha frequencies (IAF ± 2 Hz). Results demonstrated a linear shift in the psychometric function indicating a modification of perceived duration, such that progressively "faster" alpha stimulation led to longer perceived intervals. These results provide the first evidence that direct manipulations of alpha oscillations can shift perceived time in a manner consistent with a clock speed effect.

Effect of change saliency and neural entrainment on flicker-induced time dilation

When a visual stimulus flickers periodically and rhythmically, the perceived duration tends to exceed its physical duration in the peri-second range. Although flicker-induced time dilation is a robust time illusion, its underlying neural mechanisms remain inconclusive. The neural entrainment account proposes that neural entrainment of the exogenous visual stimulus, marked by steady-state visual evoked potentials (SSVEPs) over the visual cortex, is the cause of time dilation. By contrast, the saliency account argues that the conscious perception of flicker changes is indispensable. In the current study, we examined these two accounts separately. The first two experiments manipulated the level of saliency around the critical fusion threshold (CFF) in a duration discrimination task to probe the effect of change saliency. The amount of dilation correlated with the level of change saliency. The next two experiments investigated whether neural entrainment alone could also induce perceived dilation. To preclude change saliency, we utilized a combination of two high-frequency flickers above the CFF, whereas their beat frequency still theoretically aroused neural entrainment at a low frequency. Results revealed a moderate time dilation induced by combinative high-frequency flickers. Although behavioral results suggested neural entrainment engagement, electroencephalography showed neither larger power nor inter-trial coherence (ITC) at the beat. In summary, change saliency was the most critical factor determining the perception and strength of time dilation, whereas neural entrainment had a moderate influence. These results highlight the influence of higher-level visual processing on time perception.

Theta Phase-dependent Modulation of Perception by Concurrent Transcranial Alternating Current Stimulation and Periodic Visual Stimulation

Sensory perception can be modulated by the phase of neural oscillations, especially in the theta and alpha ranges. Oscillatory activity in the visual cortex can be entrained by transcranial alternating current stimulation (tACS) as well as periodic visual stimulation (i.e., flicker). Combined tACS and visual flicker stimulation modulates BOLD response, and concurrent 4-Hz auditory click train, and tACS modulate auditory perception in a phase-dependent way. In this study, we investigated whether phase synchrony between concurrent tACS and periodic visual stimulation (i.e., flicker) can modulate performance on a visual matching task. Participants completed a visual matching task on a flickering visual stimulus while receiving either in-phase (0°) or asynchronous (180°, 90°, or 270°) tACS at alpha or theta frequency. Stimulation was applied over either occipital cortex or dorsolateral pFC. Visual performance was significantly better during theta frequency tACS over the visual cortex when it was in-phase (0°) with visual stimulus flicker, compared with antiphase (180°). This effect did not appear with alpha frequency flicker or with dorsolateral pFC stimulation. Furthermore, a control sham group showed no effect. There were no significant performance differences among the asynchronous (180°, 90°, and 270°) phase conditions. Extending previous studies on visual and auditory perception, our results support a crucial role of oscillatory phase in sensory perception and demonstrate a behaviorally relevant combination of visual flicker and tACS. The spatial and frequency specificity of our results have implications for research on the functional organization of perception.

Field dependence-independence differently affects retrospective time estimation and flicker-induced time dilation

Field dependence-independence (FDI) is a stable dimension of individual functioning, transversal to different cognitive domains. While the role of some individual variables in time perception has received considerable attention, it is not clear whether and how FDI influences timing abilities. In this study, we tested the hypothesis that FDI differently affects timing performance depending on whether the task requires cognitive restructuring. Participants were assessed for FDI using the embedded figures test (EFT). They performed a prospective timing task, reproducing the duration of a flickering stimulus, and a retrospective timing task, estimating the duration of the task. We expected performance of field-dependent (FD) and field-independent (FI) individuals not to differ in the prospective task, since restructuring of task material is not needed to reproduce the stimulus duration. Conversely, we predicted that FI individuals should be more accurate than FD ones in the retrospective condition, involving restructuring skills. Results show that while both FD and FI individuals under-reproduced the stimulus duration in the prospective task, only FD participants significantly underestimated the duration of the timing task in the retrospective condition. These results suggest that differences across FD and FI individuals are apparent in timing only when the task requires high-level cognitive processing; conversely, these differences do not affect basic sensory processing.

Feature-based attentional selection affects the perceived duration of a stimulus having two superposed patterns

The perceived duration of a visual event is highly related to stimulus attributes. It is well known that a moving stimulus appears to last longer than a static one does. Previous studies have demonstrated that the time dilation in a moving stimulus can be influenced by perceived motion, rather than by mere physical motion, and that a faster motion appears to last longer than a slower one does. However, whether a top-down attentional set for the feature value can modulate the time dilation in a moving stimulus when two different visual patterns coexist within the same region of the visual field is still unknown. To test this, in Experiment 1, we presented a moving and a static random-dot pattern simultaneously within the same region, and instructed the observer to attend to one of these two patterns. The results demonstrate that perceived duration was longer when attention was directed to the moving, rather than static pattern, although both patterns physically coexisted at the same time and place and for the same duration. In Experiment 2, slow and/or fast moving patterns were presented at the same time and place, and again, feature-based attentional selection affected the perceived duration of the identical physical display. These results suggest that attention to a moving stimulus is an essential factor that determines the time dilation in a moving stimulus. This study revealed that feature-based attention, as opposed to location-based attention, plays an important role in motion-induced time dilation.

Activity in perceptual classification networks as a basis for human subjective time perception

Despite being a fundamental dimension of experience, how the human brain generates the perception of time remains unknown. Here, we provide a novel explanation for how human time perception might be accomplished, based on non-temporal perceptual classification processes. To demonstrate this proposal, we build an artificial neural system centred on a feed-forward image classification network, functionally similar to human visual processing. In this system, input videos of natural scenes drive changes in network activation, and accumulation of salient changes in activation are used to estimate duration. Estimates produced by this system match human reports made about the same videos, replicating key qualitative biases, including differentiating between scenes of walking around a busy city or sitting in a cafe or office. Our approach provides a working model of duration perception from stimulus to estimation and presents a new direction for examining the foundations of this central aspect of human experience.

Duration Perception Versus Perception Duration: A Proposed Model for the Consciously Experienced Moment

Duration perception is not the same as perception duration. Time is an object of perception in its own right and is qualitatively different to exteroceptive or interoceptive perception of concrete objects or sensations originating within the self. In reviewing evidence for and against the experienced moment, White (2017, Psychol. Bull., 143, 735–756) proposed a model of global integration of information dense envelopes of integration. This is a valuable addition to the literature because it supposes that, like Tononi’s (2004, BMC Neurosci., 5, 42) Integrated Information Theory, consciousness is an integral step above perception of objects or the self. Consciousness includes the perception of abstract contents such as time, space, and magnitude, as well as post-perceptual contents drawn from memory. The present review takes this logic a step further and sketches a potential neurobiological pathway through the salience, default mode, and central executive networks that culminates in a candidate model of how duration perception and consciousness arises. Global integration is viewed as a process of Bayesian Prediction Error Minimisation according to a model put forward by Hohwy, Paton and Palmer (2016, Phenomenol. Cogn. Sci., 15, 315–335) called ‘distrusting the present’. The proposed model also expresses global integration as an intermediate stage between perception and memory that spans an approximate one second duration, an analogue of Wittmann’s (2011, Front. Integr. Neurosci., 5, 66) experienced moment.

Perceptual Content, Not Physiological Signals, Determines Perceived Duration When Viewing Dynamic, Natural Scenes

The neural basis of time perception remains unknown. A prominent account is the pacemaker-accumulator model, wherein regular ticks of some physiological or neural pacemaker are read out as time. Putative candidates for the pacemaker have been suggested in physiological processes (heartbeat), or dopaminergic mid-brain neurons, whose activity has been associated with spontaneous blinking. However, such proposals have difficulty accounting for observations that time perception varies systematically with perceptual content. We examined physiological influences on human duration estimates for naturalistic videos between 1–64 seconds using cardiac and eye recordings. Duration estimates were biased by the amount of change in scene content. Contrary to previous claims, heart rate, and blinking were not related to duration estimates. Our results support a recent proposal that tracking change in perceptual classification networks provides a basis for human time perception, and suggest that previous assertions of the importance of physiological factors should be tempered.

The Amount of Time Dilation for Visual Flickers Corresponds to the Amount of Neural Entrainments Measured by EEG

The neural basis of time perception has long attracted the interests of researchers. Recently, a conceptual model consisting of neural oscillators was proposed and validated by behavioral experiments that measured the dilated duration in perception of a flickering stimulus (Hashimoto and Yotsumoto, 2015). The model proposed that flickering stimuli cause neural entrainment of oscillators, resulting in dilated time perception. In this study, we examined the oscillator-based model of time perception, by collecting electroencephalography (EEG) data during an interval-timing task. Initially, subjects observed a stimulus, either flickering at 10-Hz or constantly illuminated. The subjects then reproduced the duration of the stimulus by pressing a button. As reported in previous studies, the subjects reproduced 1.22 times longer durations for flickering stimuli than for continuously illuminated stimuli. The event-related potential (ERP) during the observation of a flicker oscillated at 10 Hz, reflecting the 10-Hz neural activity phase-locked to the flicker. Importantly, the longer reproduced duration was associated with a larger amplitude of the 10-Hz ERP component during the inter-stimulus interval, as well as during the presentation of the flicker. The correlation between the reproduced duration and the 10-Hz oscillation during the inter-stimulus interval suggested that the flicker-induced neural entrainment affected time dilation. While the 10-Hz flickering stimuli induced phase-locked entrainments at 10 Hz, we also observed event-related desynchronizations of spontaneous neural oscillations in the alpha-frequency range. These could be attributed to the activation of excitatory neurons while observing the flicker stimuli. In addition, neural activity at approximately the alpha frequency increased during the reproduction phase, indicating that flicker-induced neural entrainment persisted even after the offset of the flicker. In summary, our results suggest that the duration perception is mediated by neural oscillations, and that time dilation induced by flickering visual stimuli can be attributed to neural entrainment.

Periodic Fluctuation of Perceived Duration

In recent years, several studies have reported that the allocation of spatial attention fluctuates periodically. This periodic attention was revealed by measuring behavioral performance as a function of cue-to-target interval in the Posner cueing paradigm. Previous studies reported behavioral oscillations using target detection tasks. Whether the influence of periodic attention extends to cognitively demanding tasks remains unclear. To assess this, we examined the effects of periodic attention on the perception of duration. In the experiment, participants performed a temporal bisection task while a cue was presented with various cue-to-target intervals. Perceived duration fluctuated rhythmically as a function of cue-to-target interval at a group level but not at an individual level when the target was presented on the same side as the attentional cue. The results indicate that the perception of duration is influenced by periodic attention. In other words, periodic attention can influence the performance of cognitively demanding tasks such as the perception of duration.

Relative Time Compression for Slow-Motion Stimuli through Rapid Recalibration

A number of psychophysical studies have shown that moving stimuli appear to last longer than static stimuli. Here, we report that the perceived duration for slow moving stimuli can be shorter than for static stimuli under specific circumstances. Observers were tested using natural movies presented at various speeds (0.0× = static, 0.25× = slow, or 1.9× = fast, relative to original speed) and indicated whether test duration was perceived as longer or shorter than comparison movies presented at their original speed. While fast movies were perceived as longer than slow and static movies (in accordance with previous studies), we found that slow movies were perceived as shorter (i.e., time compressed) compared to static images. Similar results were obtained for artificial stimuli consisting of drifting gratings. However, time compression for slow stimuli disappeared if comparison stimuli were replaced by a white static disk that removed repetitive exposures to moving stimuli. Results suggest that duration estimation is modulated by contextual effects induced by the specific diet – or distribution – of prior visual stimuli to which observers are exposed. A simple model, which includes a rapid recalibration of human time estimation via adaptation to preceding stimuli, succeeds in reproducing our experimental data.

Flickering task-irrelevant distractors induce dilation of target duration depending upon cortical distance

Flickering stimuli are perceived to be longer than stable stimuli. This so-called “flicker-induced time dilation” has been investigated in a number of studies, but the factors critical for this effect remain unclear. We explored the spatial distribution of the flicker effect and examined how the flickering task-irrelevant distractors spatially distant from the target induce time dilation. In two experiments, we demonstrated that flickering distractors dilated the perceived duration of the target stimulus even though the target stimulus itself was stable. In addition, when the distractor duration was much longer than the target duration, a flickering distractor located ipsilateral to the target caused greater time dilation than did a contralateral distractor. Thus the amount of dilation depended on the distance between the cortical areas responsible for the stimulus locations. These findings are consistent with the recent study reporting that modulation of neural oscillators encoding the interval duration could explain flicker-induced time dilation.

On magnitudes in memory: An internal clock account of space-time interaction

Traditionally, research on time perception has diverged into a representational approach that focuses on the interaction between time and non-temporal magnitude information like spatial distance, and a mechanistic approach that emphasizes the workings and timecourse of components within an internal clock. We combined these approaches in order to identify the locus of space-time interaction effects in the mechanistic framework of the internal clock model. In three experiments, we contrasted the effects of spatial distance (a long- vs. short-distance line) on time perception with those of visual flicker (a flickering vs. static stimulus) in a duration reproduction paradigm. We found that both a flickering stimulus and a long-distance line lengthened reproduced time when presented during time encoding. However, when presented during time reproduction, a flickering stimulus shortened reproduced time but a long-distance line had no effect. The results thus show that, while visual flickers affects duration accumulation itself, spatial distance instead biases the memory of the accumulated duration. These findings are consistent with a clock-magnitude account of space-time interaction whereby both temporal duration and spatial distance are represented as mental magnitudes that can interfere with each other while being kept in memory, and places the locus of interaction between temporal and non-temporal magnitude dimensions at the memory maintenance stage of the internal clock model.

Context-Dependent Neural Modulations in the Perception of Duration

Recent neuroimaging studies have revealed that distinct brain networks are recruited in the perception of sub- and supra-second timescales, whereas psychophysical studies have suggested that there are common or continuous mechanisms for perceiving these two durations. The present study aimed to elucidate the neural implementation of such continuity by examining the neural correlates of peri-second timing. We measured neural activity during a duration reproduction task using functional magnetic resonance imaging. Our results replicate the findings of previous studies in showing that separate neural networks are recruited for sub-versus supra-second time perception: motor systems including the motor cortex and the supplementary motor area for sub-second perception, and the frontal, parietal, and auditory cortical areas for supra-second perception. We further found that the peri-second perception activated both the sub- and supra-second networks, and that the timing system that processed duration perception in previous trials was more involved in subsequent peri-second processing. These results indicate that the sub- and supra-second timing systems overlap at around 1 s, and cooperate to optimally encode duration based on the hysteresis of previous trials.

What speeds up the internal clock? Effects of clicks and flicker on duration judgements and reaction time

Four experiments investigated the effect of pre-stimulus events on judgements of the subjective duration of tones that they preceded. Experiments 1 to 4 used click trains, flickering squares, expanding circles, and white noise as pre-stimulus events and showed that (a) periodic clicks appeared to "speed up" the pacemaker of an internal clock but that the effect wore off over a click-free delay, (b) aperiodic click trains, and visual stimuli in the form of flickering squares and expanding circles, also produced similar increases in estimated tone duration, as did white noise, although its effect was weaker. A fifth experiment examined the effects of periodic flicker on reaction time and showed that, as with periodic clicks in a previous experiment, reaction times were shorter when preceded by flicker than without.

Duration Adaptation Occurs Across the Sub- and Supra-Second Systems

After repetitive exposure to a stimulus of relatively short duration, a subsequent stimulus of long duration is perceived as being even longer, and after repetitive exposure to a stimulus of relatively long duration, a subsequent stimulus of short duration is perceived as being even shorter. This phenomenon is called duration adaptation, and has been reported only for sub-second durations. We examined whether duration adaptation also occurs for supra-second durations (Experiment 1) and whether duration adaptation occurs across sub- and supra-second durations (Experiment 2). Duration adaptation occurred not only for sub-second durations, but also for supra-second durations and across sub- and supra-second durations. These results suggest that duration adaptation involves an interval-independent system or two functionally related systems that are associated with both the sub- and supra-second durations.

A framework for the first-person internal sensation of visual perception in mammals and a comparable circuitry for olfactory perception in Drosophila

Perception is a first-person internal sensation induced within the nervous system at the time of arrival of sensory stimuli from objects in the environment. Lack of access to the first-person properties has limited viewing perception as an emergent property and it is currently being studied using third-person observed findings from various levels. One feasible approach to understand its mechanism is to build a hypothesis for the specific conditions and required circuit features of the nodal points where the mechanistic operation of perception take place for one type of sensation in one species and to verify it for the presence of comparable circuit properties for perceiving a different sensation in a different species. The present work explains visual perception in mammalian nervous system from a first-person frame of reference and provides explanations for the homogeneity of perception of visual stimuli above flicker fusion frequency, the perception of objects at locations different from their actual position, the smooth pursuit and saccadic eye movements, the perception of object borders, and perception of pressure phosphenes. Using results from temporal resolution studies and the known details of visual cortical circuitry, explanations are provided for (a) the perception of rapidly changing visual stimuli, (b) how the perception of objects occurs in the correct orientation even though, according to the third-person view, activity from the visual stimulus reaches the cortices in an inverted manner and (c) the functional significance of well-conserved columnar organization of the visual cortex. A comparable circuitry detected in a different nervous system in a remote species-the olfactory circuitry of the fruit fly Drosophila melanogaster-provides an opportunity to explore circuit functions using genetic manipulations, which, along with high-resolution microscopic techniques and lipid membrane interaction studies, will be able to verify the structure-function details of the presented mechanism of perception.

Perceived duration is reduced by repetition but not by high-level expectation

A repeated stimulus is judged as briefer than a novel one. It has been suggested that this duration illusion is an example of a more general phenomenon-namely that a more expected stimulus is judged as briefer than a less expected one. To test this hypothesis, we manipulated high-level expectation through the probability of a stimulus sequence, through the regularity of the preceding stimuli in a sequence, or through whether a stimulus violates an overlearned sequence. We found that perceived duration is not reduced by these types of expectation. Repetition of stimuli, on the other hand, consistently reduces perceived duration across our experiments. In addition, the effect of stimulus repetition is constrained to the location of the repeated stimulus. Our findings suggest that estimates of subsecond duration are largely the result of low-level sensory processing.

Opposite Distortions in Interval Timing Perception for Visual and Auditory Stimuli with Temporal Modulations

When an object is presented visually and moves or flickers, the perception of its duration tends to be overestimated. Such an overestimation is called time dilation. Perceived time can also be distorted when a stimulus is presented aurally as an auditory flutter, but the mechanisms and their relationship to visual processing remains unclear. In the present study, we measured interval timing perception while modulating the temporal characteristics of visual and auditory stimuli, and investigated whether the interval times of visually and aurally presented objects shared a common mechanism. In these experiments, participants compared the durations of flickering or fluttering stimuli to standard stimuli, which were presented continuously. Perceived durations for auditory flutters were underestimated, while perceived durations of visual flickers were overestimated. When auditory flutters and visual flickers were presented simultaneously, these distortion effects were cancelled out. When auditory flutters were presented with a constantly presented visual stimulus, the interval timing perception of the visual stimulus was affected by the auditory flutters. These results indicate that interval timing perception is governed by independent mechanisms for visual and auditory processing, and that there are some interactions between the two processing systems.

Vibrotactile timing: Are vibrotactile judgements of duration affected by repetitive stimulation?

Timing in the vibrotactile modality was explored. Previous research has shown that repetitive auditory stimulation (in the form of click-trains) and visual stimulation (in the form of flickers) can alter duration judgements in a manner consistent with a "speeding up" of an internal clock. In Experiments 1 and 2 we investigated whether repetitive vibrotactile stimulation in the form of vibration trains would also alter duration judgements of either vibrotactile stimuli or visual stimuli. Participants gave verbal estimates of the duration of vibrotactile and visual stimuli that were preceded either by five seconds of 5-Hz vibration trains, or, by a five-second period of no vibrotactile stimulation, the end of which was signalled by a single vibration pulse (control condition). The results showed that durations were overestimated in the vibrotactile train conditions relative to the control condition; however, the effects were not multiplicative (did not increase with increasing stimulus duration) and as such were not consistent with a speeding up of the internal clock, but rather with an additive attentional effect. An additional finding was that the slope of the vibrotactile psychometric (control condition) function was not significantly different from that of the visual (control condition) function, which replicates a finding from a previous cross-modal comparison of timing.

Temporal frequency of events rather than speed dilates perceived duration of moving objects

In everyday life moving objects often follow irregular or repetitive trajectories for which distinctive events are potentially noticeable. It is known that the perceived duration of moving objects is distorted, but whether the distortion is due to the temporal frequency of the events or to the speed of the objects remains unclear. Disentangling the contribution of these factors to perceived duration distortions is ecologically relevant: if perceived duration were dependent on speed, it should contract with the distance from the observer to the moving objects. Here, we asked observers to estimate the perceived duration of an object rotating at different speeds and radii and found that perceived duration dilated with temporal frequency of rotations, rather than speed (or perceived speed, which we also measured). We also found that the dilation was larger for two than for one object, but the increase was not large enough to make perceived duration independent of the number of objects when expressed as a function of the local frequency (the number of times an object crossed a given location per time unit). These results suggest that perceived duration of natural stimuli containing distinctive events doesn't depend on the distance of the events to the observer.