Yuki Murai

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.

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.

The centralized and distributed nature of adaptation-induced misjudgments of time

Whether the neural representation of time is modality-independent or modality-specific is still under debate. However, temporal adaptation has recently been shown to induce perceptual misjudgments of time, which can transfer across sensory modalities for some temporal features. Indeed, recent psychophysical studies indicate that temporal frequency adaptation transfers across sensory modalities, whereas duration adaptation does not. We reviewed two neural timing models, the channel-based model and the striatal beat-frequency model, from the perspective of temporal adaptation and multisensory integration of temporal information. This paper highlights the recent developments in understanding time perception and proposes future research directions for the field.

Timescale- and Sensory Modality-Dependency of the Central Tendency of Time Perception.

When individuals are asked to reproduce intervals of stimuli that are intermixedly presented at various times, longer intervals are often underestimated and shorter intervals overestimated. This phenomenon may be attributed to the central tendency of time perception, and suggests that our brain optimally encodes a stimulus interval based on current stimulus input and prior knowledge of the distribution of stimulus intervals. Two distinct systems are thought to be recruited in the perception of sub- and supra-second intervals. Sub-second timing is subject to local sensory processing, whereas supra-second timing depends on more centralized mechanisms. To clarify the factors that influence time perception, the present study investigated how both sensory modality and timescale affect the central tendency. In Experiment 1, participants were asked to reproduce sub- or supra-second intervals, defined by visual or auditory stimuli. In the sub-second range, the magnitude of the central tendency was significantly larger for visual intervals compared to auditory intervals, while visual and auditory intervals exhibited a correlated and comparable central tendency in the supra-second range. In Experiment 2, the ability to discriminate sub-second intervals in the reproduction task was controlled across modalities by using an interval discrimination task. Even when the ability to discriminate intervals was controlled, visual intervals exhibited a larger central tendency than auditory intervals in the sub-second range. In addition, the magnitude of the central tendency for visual and auditory sub-second intervals was significantly correlated. These results suggest that a common modality-independent mechanism is responsible for the supra-second central tendency, and that both the modality-dependent and modality-independent components of the timing system contribute to the central tendency in the sub-second range.

Spatial distortion related to time compression during spatiotemporal production in Parkinson's disease

&NA; To produce coordinated manual actions within specific space and time, their relationship must be properly dealt with in a sensorimotor system. This study examined how such a coordination system might be impaired in normal aging and in Parkinsons disease (PD). Using a tablet device, young participants, elderly participants, and patients with PD were tested for concurrent production of distance and duration as well as single production of distance or duration alone. Results were analyzed in relation to deficiency of presynaptic dopamine transporter (DaT) in the striatum. We observed different patterns of impairment between normal aging and PD. Elderly participants exhibited duration overproduction when they had to produce distance and duration concurrently, but were normal in single production of either distance or duration. In contrast, PD patients exhibited normal distance production and marked underproduction of duration when either distance or duration was produced alone, but both duration and distance were underproduced when they were concurrently produced. These findings suggest that aging yields impaired performances in both elderly people and PD patients, but that temporal underproduction in PD patients entrains spatial production as if the distance to be produced were made consistent with their duration underproduction. We also observed that striatal DaT deficit was correlated with the extent of duration underproduction in PD patients. The deficit may be associated with the severe time compression and the entrainment during spatiotemporal production in PD patients. HighlightsUsing a tablet, we examined spatiotemporal production in Parkinsons disease (PD).PD exhibited normal distance and underproduced duration in single production.The duration in PD entrained spatial production during spatiotemporal processing.The duration and the entrainment were linked to dopamine transporter deficit in PD.

Optimal multisensory integration leads to optimal time estimation

Our brain compensates sensory uncertainty by combining multisensory information derived from an event, and by integrating the current sensory signal with the prior knowledge about the statistical structure of previous events. There is growing evidence that both strategies are statistically optimal; however, how these two stages of information integration interact and shape an optimal percept remains an open question. In the present study, we investigated the perception of time as an amodal perceptual attribute. The central tendency, a phenomenon of biasing the current percept toward previous stimuli, is used to quantify and model how the prior information affects the current timing behavior. We measured the timing sensitivity and the central tendency for unisensory and multisensory stimuli with sensory uncertainty systematically manipulated by adding noise. Psychophysical results demonstrate that the central tendency increases as the uncertainty increases, and that the multisensory timing improves both the timing sensitivity and the central tendency bias compared to the unisensory timing. Computational models indicate that the optimal multisensory integration precedes the optimal integration of prior information causing the central tendency. Our findings suggest that our brain incorporates the multisensory information and prior knowledge in a statistically optimal manner to realize precise and accurate timing behavior.

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.

The flash-lag effect and the flash-drag effect in the same display

Visual motion distorts the perceived position of a stimulus. In the flash-drag effect (FDE), the perceived position of a flash appears to be shifted in the direction of nearby motion. In the flash-lag effect (FLE), a flash adjacent to a moving stimulus appears to lag behind. The FLE has been explained by several models, including the differential latency hypothesis, that a moving stimulus has a shorter processing latency than a flash does. The FDE even occurs when the flash is presented earlier than the moving stimulus, and it has been discussed whether this temporal property can be explained by the differential latency model. In the present study, we simultaneously quantified the FDE and FLE using the random jump technique (Murakami, 2001b) and compared their temporal properties. While the positional offset between a randomly jumping stimulus and a flashed stimulus determined the FLE, a drifting grating appeared next to the flash at various stimulus-onset asynchronies to induce the FDE. The grating presented up to 200 ms after the flash onset induced the FDE, whose temporal tuning was explained by a simple convolution model incorporating stochastic fluctuations of differential latency estimated from the FLE data and a transient-sustained temporal profile of motion signals. Thus, a common temporal mechanism to compute the stimulus position in reference to surrounding stimuli governs both the FDE and the FLE.

Context-dependent neural modulations in the perception of duration, revealed by fMRI

Recent neuroimaging studies have revealed that two distinct brain networks are recruited in the perception of sub-second and supra-second durations. The aim of this study is to examine how intermediate duration between sub- and supra-second, that is, around one second duration, is processed in our brain. We hypothesized that durations around one second can be processed either by the sub-second system or by the supra-second system in a context-dependent matter; when the one-second stimuli are presented in the context of sub-second processing, the one-second stimuli would be processed by the sub-second system, and when they are presented in the context of supra-second processing, then, they would be processed by the supra-second system. To test our hypothesis, we measured neural correlates during the perception of duration by using functional magnetic resonance imaging (fMRI). Seventeen subjects were asked to reproduce durations of the visually presented stimuli by pressing a button. The stimulus duration was either sub-second, one-second, or supra-second. In half of the scans, trials of the one-second duration were intermixed with the trials of the sub-second durations, and in another half of the scans, trials of the one-second duration were intermixed with the trials of the supra-second durations. Firstly, we replicated previous studies by showing the separate neural networks recruited for the sub- and supra-second perceptions; visual cortex, premotor, SMA, and cerebellum for the sub-second perception, and insula and basal ganglia for the supra-second perception. Secondly, when one-second stimulus was presented with the sub-second stimulus, the visual cortex and cerebellum exhibited greater activations compared to when the stimulus was presented with the supra-second stimulus. The present results suggest that the durations around one-second could be processed either by the sub- and the supra- second system, and the visual cortex plays a part in such context-dependent modulations. Meeting abstract presented at VSS 2015.