The time course of temporal discrimination: An ERP study

Blocked versus interleaved: How range contexts modulate time perception and its EEG signatures

Accurate time perception is a crucial element in a wide range of cognitive tasks, including decision-making, memory, and motor control. One commonly observed phenomenon is that when given a range of time intervals to consider, people's estimates often cluster around the midpoint of those intervals. Previous studies have suggested that the range of these intervals can also influence our judgments, but the neural mechanisms behind this "range effect" are not yet understood. We used both behavioral tests and electroencephalographic (EEG) measures to understand how the range of sample time intervals affects the accuracy of people's subsequent time estimates. Study participants were exposed to two different setups: In the "blocked-range" (BR) session, short and long intervals were presented in separate blocks, whereas in the "interleaved-range" (IR) session, intervals of various lengths were presented randomly. Our findings indicated that the BR context led to more accurate time estimates compared to the IR context. In terms of EEG data, the BR context resulted in quicker buildup of contingent negative variation (CNV), which also reached higher amplitude levels and dissolved more rapidly during the encoding stage. We also observed an enhanced amplitude in the offset P2 component of the EEG signal. Overall, our results suggest that the variability in time intervals, as defined by their range, influences the neural processes that underlie time estimation.

Young adults and multisensory time perception: Visual and auditory pathways in comparison

The brain continuously encodes information about time, but how sensorial channels interact to achieve a stable representation of such ubiquitous information still needs to be determined. According to recent research, children show a potential interference in multisensory conditions, leading to a trade-off between two senses (sight and audition) when considering time-perception tasks. This study aimed to examine how healthy young adults behave when performing a time-perception task. In Experiment 1, we tested the effects of temporary sensory deprivation on both visual and auditory senses in a group of young adults. In Experiment 2, we compared the temporal performances of young adults in the auditory modality with those of two samples of children (sighted and sighted but blindfolded) selected from a previous study. Statistically significant results emerged when comparing the two pathways: young adults overestimated and showed a higher sensitivity to time in the auditory modality compared to the visual modality. Restricting visual and auditory input did not affect their time sensitivity. Moreover, children were more accurate at estimating time than young adults after a transient visual deprivation. This implies that as we mature, sensory deprivation does not constitute a benefit to time perception, and supports the hypothesis of a calibration process between senses with age. However, more research is needed to determine how this calibration process affects the developmental trajectories of time perception.

Common neural mechanisms supporting time judgements in humans and monkeys

There has been an increasing interest in identifying the biological underpinnings of human time perception, for which purpose research in non-human primates (NHP) is common. Although previous work, based on behaviour, suggests that similar mechanisms support time perception across species, the neural correlates of time estimation in humans and NHP have not been directly compared. In this study, we assess whether brain evoked responses during a time categorization task are similar across species. Specifically, we assess putative differences in post-interval evoked potentials as a function of perceived duration in human EEG (N = 24) and local field potential (LFP) and spike recordings in pre-supplementary motor area (pre-SMA) of one monkey. Event-related potentials (ERPs) differed significantly after the presentation of the temporal interval between "short" and "long" perceived durations in both species, even when the objective duration of the stimuli was the same. Interestingly, the polarity of the reported ERPs was reversed for incorrect trials (i.e., the ERP of a "long" stimulus looked like the ERP of a "short" stimulus when a time categorization error was made). Hence, our results show that post-interval potentials reflect the perceived (rather than the objective) duration of the presented time interval in both NHP and humans. In addition, firing rates in monkey's pre-SMA also differed significantly between short and long perceived durations and were reversed in incorrect trials. Together, our results show that common neural mechanisms support time categorization in NHP and humans, thereby suggesting that NHP are a good model for investigating human time perception.

Detecting how time is subjectively perceived based on event-related potentials (ERPs): a machine learning approach

Background and objective: Time perception is essential for the precise performance of many of our activities and the coordination between different modalities. But it is distorted in many diseases and disorders. Event-related potentials (ERP) have long been used to understand better how the human brain perceives time, but machine learning methods have rarely been used to detect a person's time perception from his/her ERPs. Methods: In this study, EEG signals of the individuals were recorded while performing an auditory oddball time discrimination task. After features were extracted from ERPs, data balancing, and feature selection, machine learning models were used to distinguish between the oddball durations of 400 ms and 600 ms from standard durations of 500 ms. ERP results showed that the P3 evoked by the 600 ms oddball stimuli appeared about 200 ms later than that of the 400 ms oddball tones. Classification performance results indicated that support vector machine (SVM) outperformed K-nearest neighbors (KNN), Random Forest, and Logistic regression models. Results: The accuracy of SVM was 91.24, 92.96, and 89.9 for the three used labeling modes, respectively. Another important finding was that most features selected for classification were in the P3 component range, supporting the observed significant effect of duration on the P3. Although all N1, P2, N2, and P3 components contributed to detecting the desired durations. Conclusion: Therefore, results of this study suggest the P3 component as a potential candidate to detect sub-second periods in future researches on brain-computer interface (BCI) applications.

Electrophysiological signatures of temporal context in the bisection task

Despite having relatively accurate timing, subjective time can be influenced by various contexts, such as stimulus spacing and sample frequency. Several electroencephalographic (EEG) components have been associated with timing, including the contingent negative variation (CNV), offset P2, and late positive component of timing (LPCt). However, the specific role of these components in the contextual modulation of perceived time remains unclear. In this study, we conducted two temporal bisection experiments to investigate this issue. Participants had to judge whether a test duration was close to a short or long standard. Unbeknownst to them, we manipulated the stimulus spacing (Experiment 1) and sample frequency (Experiment 2) to create short and long contexts while maintaining consistent test ranges and standards across different sessions. The results revealed that the bisection threshold shifted towards the ensemble mean, and both CNV and LPCt were sensitive to context modulation. In the short context, the CNV exhibited an increased climbing rate compared to the long context, whereas the LPCt displayed reduced amplitude and latency. These findings suggest that the CNV represents an expectancy wave preceding a temporal decision process, while the LPCt reflects the decision-making process itself, with both components influenced by the temporal context.

Post-interval potentials in temporal judgements

Research suggests that post-stimulus positive deflections could be associated with timing. We compared offset-locked potentials N1, P2, N1P2, and late positive component (LPC) in temporal generalization and temporal bisection-with visual probe intervals. In both tasks, the LPC amplitude decreased with the duration of the current probe interval. A larger LPC was found after shorter intervals, whereas other ERP amplitudes did not change between tasks or across durations. We also found that the LPC for different responses indicates subjective time. We discussed our findings in relation to theories of human timing.

Temporal features of concepts are grounded in time perception neural networks: An EEG study

Experimental evidence suggests that modality-specific concept features such as action, motion, and sound partially rely on corresponding action/perception neural networks in the human brain.Little is known, however, about time-related features of concepts. We examined whether temporal features of concepts recruit networks that subserve time perception in the brain in an EEG study using event and object nouns. Results showed significantly larger ERPs for event duration vs object size judgments over right parietal electrodes, a region associated with temporal processing. Additionally, alpha/beta (10-15 Hz) neural oscillation showed a stronger desynchronization for event duration compared to object size in the right parietal electrodes. This difference was not seen in control tasks comparing event vs object valence, suggesting that it is not likely to reflect a general difference between event and object nouns. These results indicate that temporal features of words may be subserved by time perception circuits in the human brain.

Dynamic and static angry faces influence time perception differently-Evidence from ERPs

The dynamic characteristics of facial expressions might affect time perception. Compared with static emotional faces, dynamic emotional faces are more intense, have higher ecological validity, and contain time series information, which may lead to time overestimation. In the present study, we aimed at investigating how dynamic characteristics of angry facial expressions affect time perception, as measured using event-related potentials (ERPs). Dynamic and static angry and neutral faces with different durations (400, 600, 800, 1000, 1200, 1400, and 1600 ms) were presented in the classical temporal bisection paradigm. Participants were asked to judge whether the duration of the presented face was closer to 400 or 1600 ms. The behavioral results showed a significant overestimation effect for dynamic angry faces compared with static faces, both in terms of proportion of long and Bisection Point. The ERP results indicated that the processing mechanisms are significantly different between judging the duration of dynamic and static angry faces. Dynamic angry faces evoked a larger N2 and Late Positive Potential than did static faces, while the static angry faces evoked a larger P2 and Early Posterior Negativity. The Contingent Negative Variation showed a complex change pattern over time. Our results indicate that dynamic angry facial expressions influence time perception differently than do static faces. Static angry faces were processed earlier and were considered to cause an overestimation of time through early emotional arousal and attentional bias, while dynamic angry faces may have caused the overestimation of time through response inhibition and late sustained attention.

When long appears short: Effects of auditory distraction on event-related potential correlates of time perception

Attentional models of time perception assume that the perceived duration of a stimulus depends on the extent to which attentional resources are allocated to its temporal information. Here, we studied the effects of auditory distraction on time perception, using a combined attentional-distraction duration-discrimination paradigm. Participants were confronted with a random sequence of long and short tone stimuli, most of which having a uniform (standard) pitch and only a few a different (deviant) pitch. As observed in previous studies, pitch-deviant tones impaired the discrimination of tone duration and triggered a sequence of event-related potentials (ERPs) reflecting a cycle of deviance detection, involuntary attentional distraction and reorientation (MMN, P3a, RON). Contrasting ERPs of short and long tone durations revealed that long tones elicited a more pronounced fronto-central contingent negative variation (CNV) in the time interval after the expected offset of the short tone as well as a more prominent centro-parietal late positive complex (LPC). Relative to standard-pitch tones, deviant-pitch tones especially impaired the correct discrimination of long tones, which was associated with a reduction of the CNV and LPC. These results are interpreted within the theoretical framework of resource-based models of time perception, in which involuntary distraction due to a deviant event led to a withdrawal of attentional resources from the processing of time information.

Post-interval EEG activity is related to task-goals in temporal discrimination

Studies investigating the neural mechanisms of time perception often measure brain activity while participants perform a temporal task. However, several of these studies are based exclusively on tasks in which time is relevant, making it hard to dissociate activity related to decisions about time from other task-related patterns. In the present study, human participants performed a temporal or color discrimination task of visual stimuli. Participants were informed which magnitude they would have to judge before or after presenting the two stimuli (S1 and S2) in different blocks. Our behavioral results showed, as expected, that performance was better when participants knew beforehand which magnitude they would judge. Electrophysiological data (EEG) was analysed using Linear Discriminant Contrasts (LDC) and a Representational Similarity Analysis (RSA) approach to investigate whether and when information about time and color was encoded. During the presentation of S1, we did not find consistent differences in EEG activity as a function of the task. On the other hand, during S2, we found that temporal and color information was encoded in a task-relevant manner. Taken together, our results suggest that task goals strongly modulate decision-related information in EEG activity.

Mapping Tonal Hierarchy in the Brain

In Western tonal music, pitches are organized hierarchically based on their perceived fit in a specific tonal context. This hierarchy forms scales that are commonly used in Western tonal music. The hierarchical nature of tonal structure is well established behaviourally; however, the neural underpinnings are largely unknown. In this study, EEG data and goodness-of-fit ratings were collected from 34 participants who listened to an arpeggio followed by a probe tone, where the probe tone could be any chromatic scale degree and the context any of the major keys. Goodness-of-fit ratings corresponded to the classic tonal hierarchy. N1, P2 and the Early Right Anterior Negativity (ERAN) were significantly modulated by scale degree. Furthermore, neural marker amplitudes and latencies were significantly correlated with similar magnitude to both pitch height and goodness-of-fit ratings. This is different from the clearer divide between pitch height correlating with early neural markers (100-200 ms) and tonal hierarchy correlating with late neural markers (200-1000 ms) reported by Sankaran et al. (2020) and Quiroga-Martinez et al. (2019). Finally, individual differences were greater than any main effects detected when pooling participants and brain-behavior correlations vary widely (i.e. r = -0.8 to 0.8).

Electrophysiological correlates of the somatotopically organized tactile duration aftereffect

Adaptation to sensory events of long or short duration leads to a negative aftereffect, in which a new target event (of median duration) following the adaptation will be perceived to be shorter or longer than is actually the case. This illusion has been observed in visual, auditory, and tactile modalities. This study used event-related potentials (ERPs) to examine the tactile duration aftereffect, using the contingent negative variation (CNV) and the late positive component (LPC) as a way to characterize the temporal processes. The tactile duration adaptation was found to induce a significant aftereffect within a somatotopic framework. Moreover, the CNV in the contralateral scalp and the LPC in the fronto-central scalp were both modulated by the tactile duration adaptation. Specifically, adaptation to a short tactile duration increased the CNV and LPC amplitudes, whereas adaptation to a long tactile duration decreased them. This modulation was contingent on the topographic distance between fingers, which was only observed when the adapting and test fingers were consistent or adjacent, but not homologous. In sum, these results reveal a coherent behavioral-electrophysiological link in the somatotopically organized tactile duration aftereffect.

Differences in the temporal processing between identification and categorization of durations: A behavioral and ERP study

This study examined how different forms of decision-making modulate time perception. Participants performed temporal bisection and generalization tasks, requiring them to either categorize a stimulus duration as more similar to short or long standards (bisection), or identify whether or not a duration was the same as a previously-presented standard (generalization). They responded faster in the bisection task than in the generalization one for long durations. This behavioral effect was accompanied by modulation of event-related potentials (ERPs). More specifically, between 500 ms and 600 ms after stimulus offset, a late positive component (LPC), appearing in the centro-parietal region, showed lower amplitude in the bisection task than in the generalization one, for long durations, mirroring the behavioral result. Before (200-500 ms) and after (600-800 ms) this window, the amplitude of the LPC was globally larger in the generalization paradigm, independently of the presented duration. Finally, the LPC amplitude was higher for long durations than for shorter ones at the beginning of the component (between 200 and 300 ms after stimulus extinction) and was then higher for short durations than for longer ones (between 300 and 600 ms after offset), indicating that the decision about the former stimuli was made earlier than for the latter ones. Taken together, these results indicate that the categorization of durations engages fewer cognitive resources than their identification.

Oscillation patterns of local field potentials in the dorsal striatum and sensorimotor cortex during the encoding, maintenance, and decision stages for the ordinal comparison of sub- and supra-second signal durations

Ordinal comparison of successively presented signal durations requires (a) the encoding of the first signal duration (standard), (b) maintenance of temporal information specific to the standard duration in memory, and (c) timing of the second signal duration (comparison) during which a comparison is made of the first and second durations. Rats were first trained to make ordinal comparisons of signal durations within three time ranges using 0.5, 1.0, and 3.0-s standard durations. Local field potentials were then recorded from the dorsal striatum and sensorimotor cortex in order to investigate the pattern of neural oscillations during each phase of the ordinal-comparison process. Increased power in delta and theta frequency ranges was observed during both the encoding and comparison stages. Active maintenance of a selected response, "shorter" or "longer" (counter-balanced across left and right levers), was represented by an increase of theta and delta oscillations in the contralateral striatum and cortex. Taken together, these data suggest that neural oscillations in the delta-theta range play an important role in the encoding, maintenance, and comparison of signal durations.

The time is "right:" Electrophysiology reveals right parietal electrode dominance in time perception

In the present study, healthy undergraduates were asked to identify if a visual stimulus appeared on screen for the same duration as a memorized target (2 s) while event-related potentials (ERP) were recorded. Trials consisted of very short (1.25 s), short (1.6 s), target (2 s), long (2.5 s) or very long (3.125 s) durations, and a yes or no response was required on each trial. We examined behavioral response as signal detection (d') and response bias via a Generalized Accuracy Coefficient (GAC). We examined the mean amplitude as well as the change in amplitude of the initial Contingent Negative Variation (iCNV) and overall CNV (oCNV) and P350 (a P300-like component that follows stimulus extinction) potentials in paired, lateralized posterior electrodes. Results showed a bias to identifying shorter trials as the target more than longer trials via negative GAC scores. The slope and amplitudes of the iCNV and oCNV were consistently greater in right parietal electrodes. Also in right parietal electrodes, the iCNV correlated to d' scores while greater P350 amplitudes in the short condition correlated with more negative GAC scores. The results indicate dominance in the right hemisphere in temporal processing for durations exceeding 1 s. The P350 should also be studied further.

Different cortical source activation patterns in children with attention deficit hyperactivity disorder during a time reproduction task

Several neurocognitive studies have indicated that children with attention-deficit/hyperactivity disorder (ADHD) exhibit cognitive deficits in perceptual timing functions; however, only a few electroencephalographic studies have investigated their time reproduction abilities. In the present research, 15 children with ADHD were studied along with 19 age-matched control subjects (aged 7-11 years) as they attempted to reproduce shorter (1000 ms) and longer (2200 ms) time intervals. Trial-mean event-related potential (ERP) and event-related spectral perturbation measures were used to compare the electroencephalography (EEG) source-level activity patterns of the ADHD and control subjects during the time-encoding and reproduction phases. For both short and long intervals, the performance of subjects with ADHD was significantly less accurate and more variable than that of the age-matched controls. During the encoding phase, the ADHD and control ERPs differed significantly for the midfrontal source cluster. The midfrontal P300 amplitude evoked by the onset of the encoding phase was significantly higher for the ADHD group. Similarly, the amplitude of contingent negative variation for the ADHD group was lower for the midfrontal independent component (IC) cluster during long-interval encoding. Theta event-related synchronization in the right occipital cluster also differed between groups during both the encoding and reproduction phases. Moreover, children with ADHD failed to show a frontal selection positivity component in the reproduction phase. Significant differences were found in the mean alpha power for the prefrontal source cluster during the time reproduction phase. These results suggest electrophysiological evidence for time perception deficiencies, selective visual processing disturbances, and working memory impairment in children with ADHD.

The impact of a concurrent motor task on auditory and visual temporal discrimination tasks

Previous studies have shown the presence of an interference effect on temporal perception when participants are required to simultaneously execute a nontemporal task. Such interference likely has an attentional source. In the present work, a temporal discrimination task was performed alone or together with a self-paced finger-tapping task used as concurrent, nontemporal task. Temporal durations were presented in either the visual or the auditory modality, and two standard durations (500 and 1,500 ms) were used. For each experimental condition, the participant's threshold was estimated and analyzed. The mean Weber fraction was higher in the visual than in the auditory modality, but only for the subsecond duration, and it was higher with the 500-ms than with the 1,500-ms standard duration. Interestingly, the Weber fraction was significantly higher in the dual-task condition, but only in the visual modality. The results suggest that the processing of time in the auditory modality is likely automatic, but not in the visual modality.

Contingent negative variation (CNV) associated with sensorimotor timing error correction

INTRODUCTION

Detection and subsequent correction of sensorimotor timing errors are fundamental to adaptive behavior. Using scalp-recorded event-related potentials (ERPs), we sought to find ERP components that are predictive of error correction performance during rhythmic movements.

METHOD

Healthy right-handed participants were asked to synchronize their finger taps to a regular tone sequence (every 600 ms), while EEG data were continuously recorded. Data from 15 participants were analyzed. Occasional irregularities were built into stimulus presentation timing: 90 ms before (advances: negative shift) or after (delays: positive shift) the expected time point. A tapping condition alternated with a listening condition in which identical stimulus sequence was presented but participants did not tap.

RESULTS

Behavioral error correction was observed immediately following a shift, with a degree of over-correction with positive shifts. Our stimulus-locked ERP data analysis revealed, 1) increased auditory N1 amplitude for the positive shift condition and decreased auditory N1 modulation for the negative shift condition; and 2) a second enhanced negativity (N2) in the tapping positive condition, compared with the tapping negative condition. In response-locked epochs, we observed a CNV (contingent negative variation)-like negativity with earlier latency in the tapping negative condition compared with the tapping positive condition. This CNV-like negativity peaked at around the onset of subsequent tapping, with the earlier the peak, the better the error correction performance with the negative shifts while the later the peak, the better the error correction performance with the positive shifts.

DISCUSSION

This study showed that the CNV-like negativity was associated with the error correction performance during our sensorimotor synchronization study. Auditory N1 and N2 were differentially involved in negative vs. positive error correction. However, we did not find evidence for their involvement in behavioral error correction. Overall, our study provides the basis from which further research on the role of the CNV in perceptual and motor timing can be developed.

Source analysis of electrophysiological correlates of beat induction as sensory-guided action

In this paper we present a reanalysis of electrophysiological data originally collected to test a sensory-motor theory of beat induction (Todd et al., 2002; Todd and Seiss, 2004; Todd and Lee, 2015). The reanalysis is conducted in the light of more recent findings and in particular the demonstration that auditory evoked potentials contain a vestibular dependency. At the core of the analysis is a model which predicts brain dipole source current activity over time in temporal and frontal lobe areas during passive listening to a rhythm, or active synchronization, where it dissociates the frontal activity into distinct sources which can be identified as respectively pre-motor and motor in origin. The model successfully captures the main features of the rhythm in showing that the metrical structure is manifest in an increase in source current activity during strong compared to weak beats. In addition the outcomes of modeling suggest that: (1) activity in both temporal and frontal areas contribute to the metrical percept and that this activity is distributed over time; (2) transient, time-locked activity associated with anticipated beats is increased when a temporal expectation is confirmed following a previous violation, such as a syncopation; (3) two distinct processes are involved in auditory cortex, corresponding to tangential and radial (possibly vestibular dependent) current sources. We discuss the implications of these outcomes for the insights they give into the origin of metrical structure and the power of syncopation to induce movement and create a sense of groove.

Repetition enhancement and memory effects for duration

A remarkable aspect of conscious perception is that moments carryover from one to the next, also known as temporal continuity. This ability is thus crucial for detecting regularities, such as in speech and music, and may rely on an accurate perception of time. Investigations of human time perception have detailed two electroencephalographic (EEG) components associated with timing, the contingent negative variation (CNV) and late positive component of timing (LPCt); however, the precise roles of these components in timing remain elusive. Recently, we demonstrated that the perception of duration is influenced by durations presented on prior trials, which we explained by the creation of an implicit memory standard that adapts to local changes in sequence presentation. Here, we turn to the neural basis of this effect. Human participants performed a temporal bisection task in which they were required to classify the duration of auditory stimuli into short and long duration categories; crucially, the presentation order was first-order counterbalanced, allowing us to measure the effect of each presented duration on the next. EEG recordings revealed that the CNV and LPCt signals both covaried with the duration presented on the current trial, with CNV predicting reaction time and LPCt predicting choice. Additionally, both signals covaried with the duration presented in the prior trial but in different ways, with the CNV amplitude reflecting the change in the memory standard and the LPCt reflecting decision uncertainty. Furthermore, we observed a repetition enhancement effect of duration only for the CNV, suggesting that this signal additionally indexes the similarity of successive durations. These findings demonstrate dissociable roles for the CNV and LPCt, and demonstrate that both signals are continuously updated on a trial-by-trial basis that reflects shifts in temporal decisions.

Oscillatory multiplexing of neural population codes for interval timing and working memory

Interval timing and working memory are critical components of cognition that are supported by neural oscillations in prefrontal-striatal-hippocampal circuits. In this review, the properties of interval timing and working memory are explored in terms of behavioral, anatomical, pharmacological, and neurophysiological findings. We then describe the various neurobiological theories that have been developed to explain these cognitive processes - largely independent of each other. Following this, a coupled excitatory - inhibitory oscillation (EIO) model of temporal processing is proposed to address the shared oscillatory properties of interval timing and working memory. Using this integrative approach, we describe a hybrid model explaining how interval timing and working memory can originate from the same oscillatory processes, but differ in terms of which dimension of the neural oscillation is utilized for the extraction of item, temporal order, and duration information. This extension of the striatal beat-frequency (SBF) model of interval timing (Matell and Meck, 2000, 2004) is based on prefrontal-striatal-hippocampal circuit dynamics and has direct relevance to the pathophysiological distortions observed in time perception and working memory in a variety of psychiatric and neurological conditions.

The duration of disgusted and fearful faces is judged longer and shorter than that of neutral faces: the attention-related time distortions as revealed by behavioral and electrophysiological measurements

Time perception has been shown to be altered by emotions. This study employed event-related potentials (ERPs) to examine the effects of two threat-related emotions on the judgment of time intervals in the range of 490–910 ms. We demonstrated that disgust and fear have distinct influences on time perception. At the behavioral level, disgusted faces were estimated longer and fearful faces were estimated shorter (i.e., the generalization gradient for the disgusted faces was shifted left while the generalization gradient for the fearful faces was shifted right) when compared with neutral faces. Accordingly, the contingent negative variation, an online ERP index of timing, displayed larger area in disgust and smaller area in fear conditions when compared with neutral condition (disgust = 1.94 ± 2.35 μV_•s, neutral = 1.40 ± 2.5 μV_•s, and fear = 1.00 ± 2.26 μV_•s). These findings indicated that specific neural mechanisms may underlie the attention effects of different subtypes of threat-related emotions on timing; compared with neutral faces, fearful faces are likely to attract more attentional resources while disgusted faces may attract less attentional resources for emotional processing. The major contribution of the current study is to provide neural correlates of fear vs. disgust divergence in the aspect of time perception and to demonstrate beyond the behavioral level that the categorization of threat-related emotions should be refined so to highlight the adaptability of the human defense system.

Decoupling interval timing and climbing neural activity: a dissociation between CNV and N1P2 amplitudes

It is often argued that climbing neural activity, as for example reflected by the contingent negative variation (CNV) in the electroencephalogram, is the signature of the subjective experience of time. According to this view, the resolution of the CNV coincides with termination of subjective timing processes. Paradoxically, behavioral data indicate that participants keep track of timing even after the standard interval (SI) has passed. This study addresses whether timing continues after CNV resolution. In Experiment 1, human participants were asked to discriminate time intervals while evoked potentials (EPs) elicited by the sound terminating a comparison interval (CI) were measured. As the amplitude of N1P2 components increases as a function of the temporal distance from the SI, and the latency of the P2 component followed the hazard rate of the CIs, timing processes continue after CNV resolution. Based on a novel experimental paradigm, statistical model comparisons and trial-by-trial analyses, Experiment 2 supports this finding as subjective time is more accurately indexed by the amplitude of early EPs than by CNV amplitude. These results provide the first direct evidence that subjective timing of multisecond intervals does not depend on climbing neural activity as indexed by the CNV and that the subjective experience of time is better reflected by distinct features of post-CI evoked potentials.

Probing interval timing with scalp-recorded electroencephalography (EEG)

Humans, and other animals, are able to easily learn the durations of events and the temporal relationships among them in spite of the absence of a dedicated sensory organ for time. This chapter summarizes the investigation of timing and time perception using scalp-recorded electroencephalography (EEG), a non-invasive technique that measures brain electrical potentials on a millisecond time scale. Over the past several decades, much has been learned about interval timing through the examination of the characteristic features of averaged EEG signals (i.e., event-related potentials, ERPs) elicited in timing paradigms. For example, the mismatch negativity (MMN) and omission potential (OP) have been used to study implicit and explicit timing, respectively, the P300 has been used to investigate temporal memory updating, and the contingent negative variation (CNV) has been used as an index of temporal decision making. In sum, EEG measures provide biomarkers of temporal processing that allow researchers to probe the cognitive and neural substrates underlying time perception.

The passive CNV: carving out the contribution of task-related processes to expectancy

In this perspective article, I summarized certain theoretical and methodological issues concerning the investigation of the contribution of cognitive and motor processes to the electrophysiological stimulus-preceding activity. In particular, the question of whether the contingent negative variation (CNV) is a marker reflecting both cognitive expectancy and motor preparation in the S1-S2 paradigms was discussed. New evidence suggests that it is possible to isolate an automatic temporal expectancy-related cognitive mechanism relying on a passive CNV after ruling out the contribution of task-related processes, including motor and decisional processes, to it. This can be achieved by simply manipulating the trial temporal structure according to a probabilistic, oddball distribution. The scientific value of this finding is framed within a historical perspective in the attempt to bridge together the classic literature linking the CNV to stimulus preparation and the more recently published literature linking the CNV to temporal processing.

Automatic temporal expectancy: a high-density event-related potential study

How we compute time is not fully understood. Questions include whether an automatic brain mechanism is engaged in temporally regular environmental structure in order to anticipate events, and whether this can be dissociated from task-related processes, including response preparation, selection and execution. To investigate these issues, a passive temporal oddball task requiring neither time-based motor response nor explicit decision was specifically designed and delivered to participants during high-density, event-related potentials recording. Participants were presented with pairs of audiovisual stimuli (S1 and S2) interspersed with an Inter-Stimulus Interval (ISI) that was manipulated according to an oddball probabilistic distribution. In the standard condition (70% of trials), the ISI lasted 1,500 ms, while in the two alternative, deviant conditions (15% each), it lasted 2,500 and 3,000 ms. The passive over-exposition to the standard ISI drove participants to automatically and progressively create an implicit temporal expectation of S2 onset, reflected by the time course of the Contingent Negative Variation response, which always peaked in correspondence to the point of S2 maximum expectation and afterwards inverted in polarity towards the baseline. Brain source analysis of S1- and ISI-related ERP activity revealed activation of sensorial cortical areas and the supplementary motor area (SMA), respectively. In particular, since the SMA time course synchronised with standard ISI, we suggest that this area is the major cortical generator of the temporal CNV reflecting an automatic, action-independent mechanism underlying temporal expectancy.

Parietal influence on temporal encoding indexed by simultaneous transcranial magnetic stimulation and electroencephalography

Previous studies have suggested that contingent negative variation (CNV), as recorded by electroencaphalography (EEG), may serve as an index of temporal encoding. The interpretation of these studies is complicated by the fact that, in a majority of studies, the CNV signal was obtained at a time when subjects were not only registering stimulus duration but also making decisions and preparing to act. Previously, we demonstrated that repetitive transcranial magnetic stimulation (rTMS) of the right supramarginal gyrus (rSMG) in humans lengthened the perceived duration of a visual stimulus (Wiener et al., 2010a), suggesting the rSMG is involved in basic encoding processes. Here, we report a replication of this effect with simultaneous EEG recordings during the encoding of stimulus duration. Stimulation of the rSMG led to an increase in perceived duration and the amplitude of N1 and CNV components recorded from frontocentral sites. Furthermore, the size of the CNV amplitude, but not N1, positively correlated with the size of the rTMS effect but negatively correlated with bias (the baseline tendency to report a comparison stimulus as shorter), suggesting that the CNV indexes stimulus duration. These results suggest that a feedforward mechanism from parietal to prefrontal regions mediates temporal encoding and demonstrate a dissociation between early and late phases of encoding processes.

Functional imaging of the cerebellum and basal ganglia during predictive motor timing in early Parkinson's disease

BACKGROUND AND PURPOSE

The basal ganglia and the cerebellum have both emerged as important structures involved in the processing of temporal information.

METHODS

We examined the roles of the cerebellum and striatum in predictive motor timing during a target interception task in healthy individuals (HC group; n = 21) and in patients with early Parkinson's disease (early stage PD group; n = 20) using functional magnetic resonance imaging.

RESULTS

Despite having similar hit ratios, the PD failed more often than the HC to postpone their actions until the right moment and to adapt their behavior from one trial to the next. We found more activation in the right cerebellar lobule VI in HC than in early stage PD during successful trials. Successful trial-by-trial adjustments were associated with higher activity in the right putamen and lobule VI of the cerebellum in HC.

CONCLUSIONS

We conclude that both the cerebellum and striatum are involved in predictive motor timing tasks. The cerebellar activity is associated exclusively with the postponement of action until the right moment, whereas both the cerebellum and striatum are needed for successful adaptation of motor actions from one trial to the next. We found a general ''hypoactivation'' of basal ganglia and cerebellum in early stage PD relative to HC, indicating that even in early stages of the PD there could be functional perturbations in the motor system beyond striatum.

Temporal accumulation and decision processes in the duration bisection task revealed by contingent negative variation

The duration bisection paradigm is a classic task used to examine how humans and other animals perceive time. Typically, participants first learn short and long anchor durations and are subsequently asked to classify probe durations as closer to the short or long anchor duration. However, the specific representations of time and the decision rules applied in this task remain the subject of debate. For example, researchers have questioned whether participants actually use representations of the short and long anchor durations in the decision process rather than merely a response threshold that is derived from those anchor durations. Electroencephalographic (EEG) measures, like the contingent negative variation (CNV), can provide information about the perceptual and cognitive processes that occur between the onset of the timing stimulus and the motor response. The CNV has been implicated as an electrophysiological marker of interval timing processes such as temporal accumulation, representation of the target duration, and the decision that the target duration has been attained. We used the CNV to investigate which durations are involved in the bisection categorization decision. The CNV increased in amplitude up to the value of the short anchor, remained at a constant level until about the geometric mean (GM) of the short and long anchors, and then began to resolve. These results suggest that the short anchor and the GM of the short and long anchors are critical target durations used in the bisection categorization decision process. In addition, larger mean N1P2 amplitude differences were associated with larger amplitude CNVs, which may reflect the participant’s precision in initiating timing on each trial across a test session. Overall, the results demonstrate the value of using scalp-recorded EEG to address basic questions about interval timing.

Slow potentials in time estimation: the role of temporal accumulation and habituation

Numerous studies have shown that contingent negative variation (CNV) measured at fronto-central and parietal-central areas is closely related to interval timing. However, the exact nature of the relation between CNV and the underlying timing mechanisms is still a topic of discussion. On the one hand, it has been proposed that the CNV measured at supplementary motor area (SMA) is a direct reflection of the unfolding of time since a perceived onset, whereas other work has suggested that the increased amplitude reflects decision processes involved in interval timing. Strong evidence for the first view has been reported by Macar et al. (1999), who showed that variations in temporal performance were reflected in the measured CNV amplitude. If the CNV measured at SMA is a direct function of the passing of time, habituation effects are not expected. Here we report two replication studies, which both failed to replicate the expected performance-dependent variations. Even more powerful linear-mixed effect analyses failed to find any performance related effects on the CNV amplitude, whereas habituation effects were found. These studies therefore suggest that the CNV amplitude does not directly reflect the unfolding of time.