The inner sense of time: how the brain creates a representation of duration

Mindfulness and time perception: A systematic integrative review

Several recent studies have explored the relationships between mindfulness and time perception, an area of research that has become increasingly popular in the last 10-15 years. In this article, we present a systematic integrative review of the evidence on this subject. We also integrate the field's findings into a conceptual framework which considers the multifaceted nature of both mindfulness, and time perception research. To identify the relevant literature, we searched the following databases using relevant keywords: PsycINFO; Medline; EBSCO Host Psychology and Behavioral Sciences Collection; and Web of Science. These searches were last performed on the 4th of May 2022, and additional hand searches were also conducted. To be included, articles had to be in English and contain original data about the potential relationship(s) between mindfulness and time perception. Articles which did not present usable data about the relationship(s) between the variables of interest were excluded. In total, 47 research articles were included in the review (combined sample size of ∼5800 participants). Risks of bias in the selected studies were evaluated using two separate assessment tools designed for this purpose. Through an integrative narrative synthesis, this article reviews how mindfulness may relate to time perception for various reference frames, and for various time perception measures and methods. It also provides new insights by exploring how a wide range of findings can be integrated into a coherent whole, in light of some relevant time perception models and mindfulness theories. Altogether, the reviewed data suggest the existence of complex and multifaceted relationships between mindfulness and time perception, highlighting the importance of considering many factors when planning research or interpreting data in this field. Limitations of the current review include the scarceness of data for certain categories of findings, and the relatively low prevalence of studies with a randomized controlled design in the source literature. This research was partly funded by a grant from the Natural Science and Engineering Research Council of Canada.

A cerebellar granule cell-climbing fiber computation to learn to track long time intervals

In classical cerebellar learning, Purkinje cells (PkCs) associate climbing fiber (CF) error signals with predictive granule cells (GrCs) that were active just prior (∼150 ms). The cerebellum also contributes to behaviors characterized by longer timescales. To investigate how GrC-CF-PkC circuits might learn seconds-long predictions, we imaged simultaneous GrC-CF activity over days of forelimb operant conditioning for delayed water reward. As mice learned reward timing, numerous GrCs developed anticipatory activity ramping at different rates until reward delivery, followed by widespread time-locked CF spiking. Relearning longer delays further lengthened GrC activations. We computed CF-dependent GrC→PkC plasticity rules, demonstrating that reward-evoked CF spikes sufficed to grade many GrC synapses by anticipatory timing. We predicted and confirmed that PkCs could thereby continuously ramp across seconds-long intervals from movement to reward. Learning thus leads to new GrC temporal bases linking predictors to remote CF reward signals-a strategy well suited for learning to track the long intervals common in cognitive domains.

Parallel processes of temporal control in the supplementary motor area and the frontoparietal circuit

Durations in the several seconds' range are cognitively accessible during active timing. Functional neuroimaging studies suggest the engagement of the basal ganglia (BG) and supplementary motor area (SMA). However, their functional relevance and arrangement remain unclear because non-timing cognitive processes temporally coincide with the active timing. To examine the potential contamination by parallel processes, we introduced a sensory control and a motor control to the duration-reproduction task. By comparing their hemodynamic functions, we decomposed the neural activities in multiple brain loci linked to different cognitive processes. Our results show a dissociation of two cortical neural circuits: the SMA for both active timing and motor preparation, followed by a prefrontal-parietal circuit related to duration working memory. We argue that these cortical processes represent duration as the content but at different levels of abstraction, while the subcortical structures, including the BG and thalamus, provide the logistic basis of timing by coordinating the temporal framework across brain structures.

Impact of babyface schema on time perception: Insights from neutral and crying facial expressions

Facial expressions in infants have been noted to create a spatial attention bias when compared with adult faces. Yet, there is limited understanding of how adults perceive the timing of infant facial expressions. To investigate this, we used both infant and adult facial expressions in a temporal bisection task. In Experiment 1, we compared duration judgments of neutral infant and adult faces. The results revealed that participants felt that neutral infant faces lasted for a shorter time than neutral adult faces, independent of participant sex. Experiment 2 employed sad (crying) facial expressions. Here, the female participants perceived that the infants' faces were displayed for a longer duration than the adults' faces, whereas this distinction was not evident among the male participants. These findings highlight the influence of the babyface schema on time perception, nuanced by emotional context and sex-based individual variances.

Insular and prelimbic cortices control behavioral accuracy and precision in a temporal decision-making task in rats

The anterior insular cortex (AIC) comprises a region of sensory integration. It appears to detect salient events in order to guide goal-directed behavior, code tracking errors, and estimate the passage of time. Temporal processing in the AIC may be instantiated by the integration of representations of interoception. Projections between the AIC and the medial prefrontal cortex (mPFC) - found both in rats and humans - also suggest a possible role for these structures in the integration of autonomic responses during ongoing behavior. Few studies, however, have investigated the role of AIC and mPFC in decision-making and time estimation tasks. Moreover, their findings are not consistent, so the relationship between temporal decision-making and those areas remains unclear. The present study employed bilateral inactivations to explore the role of AIC and prelimbic cortex (PL) in rats during a temporal decision-making task. In this task, two levers are available simultaneously (but only one is active), one predicting reinforcement after a short, and the other after a long-fixed interval. Optimal performance requires a switch from the short to the long lever after the short-fixed interval elapsed and no reinforcement was delivered. Switch behavior from the short to the long lever was dependent on AIC and PL. During AIC inactivation, switch latencies became more variable, while during PL inactivation switch latencies became both more variable and less accurate. These findings point to a dissociation between AIC and PL in temporal decision-making, suggesting that the AIC is important for temporal precision, and PL is important for both temporal accuracy and precision.

Induction of altered states of consciousness during Floatation-REST is associated with the dissolution of body boundaries and the distortion of subjective time

Floatation-REST (Reduced Environmental Stimulation Therapy) minimizes stimulation of the nervous system by immersing subjects in an environment without sound or light while they effortlessly float in thermoneutral water supersaturated with Epsom salt. Here we investigated the relationship between altered states of consciousness (ASC) and its association with the affective changes induced by Floatation-REST. Using a within-subject crossover design, 50 healthy subjects were randomized to 60 min of Floatation-REST or 60 min of Bed-REST (an active control condition that entailed lying supine on a warm waterbed in a dark and quiet room). Following Floatation-REST, subjects felt significantly more relaxed, less anxious, and less tired than after Bed-REST. Floatation-REST also induced significantly more pronounced ASC characterized by the dissolution of body boundaries and the distortion of subjective time. The loss of body boundaries mediated the loss of anxiety, revealing a novel mechanism by which Floatation-REST exerts its anxiolytic effect.

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.

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.

The Effect of Emotion on Time Perception in Youth Athletes with Different Alerting Efficiencies

Purpose

Time perception plays a critical role in executing movements in various competitions. However, less research has been conducted on the alerting component of attention in the processing of time perception, and that the effects of emotion on the alerting network show inconsistent effects. This study is aimed to explore the factors that may influence time perception in youth athletes and these relationships.

Methods

A total of 225 participants were recruited to assess alerting efficiency using the Attention Network Test and were divided into high and low alerting efficiency groups based on the front and back 27% of the ranked alerting scores as a dividing metric, and subsequently participants completed Time replication task under different emotionally induced conditions.

Results

Alerting efficiency had a significant effect on time perception, with the high alerting efficiency subjects having higher time estimation accuracy [F (1106) = 6.32, p = 0.013, η2p = 0.10] and being more inclined to overestimate time perception [F (1106) = 12.64, p = 0.001, η2 p = 0.11]. An interaction was found between emotion and alerting efficiency on time replication ratio [F (2106) = 3.59, p = 0.031, η2p = 0.08], and further simple effects analyses found that the low alerting efficiency subjects tended to overestimate time in the anger state relative to the happy and neutral states [F (2106) = 5.93, p < 0.01, η2p = 0.10].

Conclusion

These findings suggest that high alerting efficiency in youth athletes is associated with greater time perception response advantage; The time perception of low alerting efficiency youth athletes was more likely to be affected by emotions. This study provides a reference for the training of time perception and specialized perceptual ability of youth athletes, enriches the index system of psychological selection of youth athletes.

Superior Attentional Efficiency of Auditory Cue via the Ventral Auditory-thalamic Pathway

Auditory commands are often executed more efficiently than visual commands. However, empirical evidence on the underlying behavioral and neural mechanisms remains scarce. In two experiments, we manipulated the delivery modality of informative cues and the prediction violation effect and found consistently enhanced RT benefits for the matched auditory cues compared with the matched visual cues. At the neural level, when the bottom-up perceptual input matched the prior prediction induced by the auditory cue, the auditory-thalamic pathway was significantly activated. Moreover, the stronger the auditory-thalamic connectivity, the higher the behavioral benefits of the matched auditory cue. When the bottom-up input violated the prior prediction induced by the auditory cue, the ventral auditory pathway was specifically involved. Moreover, the stronger the ventral auditory-prefrontal connectivity, the larger the behavioral costs caused by the violation of the auditory cue. In addition, the dorsal frontoparietal network showed a supramodal function in reacting to the violation of informative cues irrespective of the delivery modality of the cue. Taken together, the results reveal novel behavioral and neural evidence that the superior efficiency of the auditory cue is twofold: The auditory-thalamic pathway is associated with improvements in task performance when the bottom-up input matches the auditory cue, whereas the ventral auditory-prefrontal pathway is involved when the auditory cue is violated.

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.

A Second Introduction to the Neurobiology of Interval Timing

Time is a critical variable that organisms must be able to measure in order to survive in a constantly changing environment. Initially, this paper describes the myriad of contexts where time is estimated or predicted and suggests that timing is not a single process and probably depends on a set of different neural mechanisms. Consistent with this hypothesis, the explosion of neurophysiological and imaging studies in the last 10 years suggests that different brain circuits and neural mechanisms are involved in the ability to tell and use time to control behavior across contexts. Then, we develop a conceptual framework that defines time as a family of different phenomena and propose a taxonomy with sensory, perceptual, motor, and sensorimotor timing as the pillars of temporal processing in the range of hundreds of milliseconds.

Coordinate-Based Meta-Analyses of the Time Perception Network

The study of time perception has advanced over the past three decades to include numerous neuroimaging studies, most notably including the use of functional Magnetic Resonance Imaging (fMRI). Yet, with this increase in studies, there comes the desire to draw broader conclusions across datasets about the nature and instantiation of time in the human brain. In the absence of collating individual studies together, the field has employed the use of Coordinate-Based Meta-Analyses (CBMA), in which foci from individual studies are modeled as probability distributions within the brain, from which common areas of activation-likelihood are determined. This chapter provides an overview of these CBMA studies, the methods they employ, the conclusions drawn by them, and where future areas of inquiry lie. The result of this survey suggests the existence of a domain-general "timing network" that can be used both as a guide for individual neuroimaging studies and as a template for future meta-analyses.

Temporal Information Processing in the Cerebellum and Basal Ganglia

Temporal information processing in the range of a few hundred milliseconds to seconds involves the cerebellum and basal ganglia. In this chapter, we present recent studies on nonhuman primates. In the studies presented in the first half of the chapter, monkeys were trained to make eye movements when a certain amount of time had elapsed since the onset of the visual cue (time production task). The animals had to report time lapses ranging from several hundred milliseconds to a few seconds based on the color of the fixation point. In this task, the saccade latency varied with the time length to be measured and showed stochastic variability from one trial to the other. Trial-to-trial variability under the same conditions correlated well with pupil diameter and the preparatory activity in the deep cerebellar nuclei and the motor thalamus. Inactivation of these brain regions delayed saccades when asked to report subsecond intervals. These results suggest that the internal state, which changes with each trial, may cause fluctuations in cerebellar neuronal activity, thereby producing variations in self-timing. When measuring different time intervals, the preparatory activity in the cerebellum always begins approximately 500 ms before movements, regardless of the length of the time interval being measured. However, the preparatory activity in the striatum persists throughout the mandatory delay period, which can be up to 2 s, with different rate of increasing activity. Furthermore, in the striatum, the visual response and low-frequency oscillatory activity immediately before time measurement were altered by the length of the intended time interval. These results indicate that the state of the network, including the striatum, changes with the intended timing, which lead to different time courses of preparatory activity. Thus, the basal ganglia appear to be responsible for measuring time in the range of several hundred milliseconds to seconds, whereas the cerebellum is responsible for regulating self-timing variability in the subsecond range. The second half of this chapter presents studies related to periodic timing. During eye movements synchronized with alternating targets at regular intervals, different neurons in the cerebellar nuclei exhibit activity related to movement timing, predicted stimulus timing, and the temporal error of synchronization. Among these, the activity associated with target appearance is particularly enhanced during synchronized movements and may represent an internal model of the temporal structure of stimulus sequence. We also considered neural mechanism underlying the perception of periodic timing in the absence of movement. During perception of rhythm, we predict the timing of the next stimulus and focus our attention on that moment. In the missing oddball paradigm, the subjects had to detect the omission of a regularly repeated stimulus. When employed in humans, the results show that the fastest temporal limit for predicting each stimulus timing is about 0.25 s (4 Hz). In monkeys performing this task, neurons in the cerebellar nuclei, striatum, and motor thalamus exhibit periodic activity, with different time courses depending on the brain region. Since electrical stimulation or inactivation of recording sites changes the reaction time to stimulus omission, these neuronal activities must be involved in periodic temporal processing. Future research is needed to elucidate the mechanism of rhythm perception, which appears to be processed by both cortico-cerebellar and cortico-basal ganglia pathways.

A common timing mechanism across different millisecond domains: evidence from perceptual and motor tasks

Temporal information processing (TIP) constitutes a complex construct that underlies many cognitive functions and operates in a few hierarchically ordered time domains. This study aimed to verify the relationship between the tens of milliseconds and hundreds of milliseconds domains, referring to perceptual and motor timing, respectively. Sixty four young healthy individuals participated in this study. They underwent two auditory temporal order judgement tasks to assess their performance in the tens of milliseconds domain; on this basis, groups of high-level performers (HLP) and low-level performers (LLP) were identified. Then, a maximum tapping task was used to evaluate performance in the hundreds of milliseconds domain. The most remarkable result was that HLP achieved a faster tapping rate and synchronised quicker with their "internal clock" during the tapping task than did LLP. This result shows that there is a relationship between accuracy in judging temporally asynchronous stimuli and ability to achieve and maintain the pace of a movement adequate to one's internal pacemaker. This could indicate the strong contribution of a common timing mechanism, responsible for temporal organisation and coordination of behaviours across different millisecond domains.

Me, myself and you: How self-consciousness influences time perception

Several investigations have shown that the processing of self-relevant information differs from processing objective information. The present study aimed to investigate the effect of social stimuli on subjective time processing. Here, social stimuli are images of an unknown male and female person and an image of participants' self. Forty university students were tested with a time reproduction task in which they were asked to reproduce the duration of the stimulus previously presented. Images of others or themselves were used to mark the temporal intervals. Participants also performed questionnaires to evaluate the level of anxiety and depression as well as self-consciousness. A generalised linear mixed-effects model approach was adopted. Results showed that male participants with higher Private Self-Consciousness scores showed higher time perception accuracy than females. Also, female participants reported higher scores for the Public Self-Consciousness subscale than male participants. The findings are discussed in terms of social context models of how attention is solicited and arousal is generated by social stimuli, highlighting the effect of social context on subjective perception of time.

Time processing in neurological and psychiatric conditions

A central question in understanding cognition and pathology-related cognitive changes is how we process time. However, time processing difficulties across several neurological and psychiatric conditions remain seldom investigated. The aim of this review is to develop a unifying taxonomy of time processing, and a neuropsychological perspective on temporal difficulties. Four main temporal judgments are discussed: duration processing, simultaneity and synchrony, passage of time, and mental time travel. We present an integrated theoretical framework of timing difficulties across psychiatric and neurological conditions based on selected patient populations. This framework provides new mechanistic insights on both (a) the processes involved in each temporal judgement, and (b) temporal difficulties across pathologies. By identifying underlying transdiagnostic time-processing mechanisms, this framework opens fruitful avenues for future research.

Lost in time: Relocating the perception of duration outside the brain

It is well-accepted in neuroscience that animals process time internally to estimate the duration of intervals lasting between one and several seconds. More than 100 years ago, Henri Bergson nevertheless remarked that, because animals have memory, their inner experience of time is ever-changing, making duration impossible to measure internally and time a source of change. Bergson proposed that quantifying the inner experience of time requires its externalization in movements (observed or self-generated), as their unfolding leaves measurable traces in space. Here, studies across species are reviewed and collectively suggest that, in line with Bergson's ideas, animals spontaneously solve time estimation tasks through a movement-based spatialization of time. Moreover, the well-known scalable anticipatory responses of animals to regularly spaced rewards can be explained by the variable pressure of time on reward-oriented actions. Finally, the brain regions linked with time perception overlap with those implicated in motor control, spatial navigation and motivation. Thus, instead of considering time as static information processed by the brain, it might be fruitful to conceptualize it as a kind of force to which animals are more or less sensitive depending on their internal state and environment.

Time bisection and reproduction: Evidence for a slowdown of the internal clock in right brain damaged patients

Previous studies show that the right hemisphere is involved in time processing, and that damage to the right hemisphere is associated with a tendency to perceive time intervals as shorter than they are, and to reproduce time intervals as longer than they are. Whether time processing deficits following right hemisphere damage are related and what is their neurocognitive basis is unclear. In this study, right brain damaged (RBD) patients, left brain damaged (LBD) patients, and healthy controls underwent a time bisection task and a time reproduction task involving time intervals varying between each other by milliseconds (short durations) or seconds (long durations). The results show that in the time bisection task RBD patients underestimated time intervals compared to LBD patients and healthy controls, while they reproduced time intervals as longer than they are. Time underestimation and over-reproduction in RBD patients applied to short but not long time intervals, and were correlated. Voxel-based lesion-symptom mapping (VLSM) showed that time underestimation was associated with lesions to a right cortico-subcortical network involving the insula and inferior frontal gyrus. A small portion of this network was also associated with time over-reproduction. Our findings are consistent with a slowdown of an 'internal clock' timing mechanism following right brain damage, which likely underlies both the underestimation and the over-reproduction of time intervals, and their (overlapping) neural bases.

Maximal and Submaximal Intensity Isometric Knee Extensions Induce an Underestimation of Time Estimates with Both Younger And Older Adults: A Randomized Crossover Trial

Our perception of time plays a critical role in nearly all daily activities and especially in sports. There are no studies that have investigated and compared time perception during exercise in young and older adults. Thus, this study aimed to compare the effects of exercise on time perception between younger and older adult populations. Thirty-three recreationally active participants were recruited and assigned to either the younger (university students, 9 males and 10 females) or older adults (>60 years, 8 males and 6 females). All participants completed four exercise conditions over two sessions on separate days: approximately 30-seconds of knee extensors 100%, 60% and 10% of maximum voluntary isometric contraction (MVIC), and control (no contractions). Prospective time perception was estimated (at 5-, 10-, 20-, and 30-seconds) at the beginning of each session and while performing the exercise. A main effect for condition (p < 0.001, d = 1.06) with subsequent post-hoc tests indicated participants significantly underestimated (estimated time was shorter than chronological time) time in all three exercise conditions compared to the control. There were no significant age group differences. In conclusion, exercise underestimated time estimates regardless of intensity or age. This questions the postulated intensity-dependent relationship between exercise and time perception. While older adults were expected to be less accurate in their time estimates, they may have been able to adopt alternative strategies for age-related changes in their internal clock, resulting in no significant age group differences.

The role of depressive symptoms in the interplay between aging and temporal processing

Temporal processing, the ability to mentally represent and process the dynamical unfolding of events over time, is a fundamental feature of cognition that evolves with advancing age. Aging has indeed been associated with slower and more variable performance in timing tasks. However, the role of depressive symptoms in age-related changes in temporal processing remains to be investigated. Therefore, the present work aims to shed light on the link between temporal processing and depressive symptoms, which are frequent with advancing age. We relied on the multicentric "Blursday Project" database, providing measures of temporal processing together with questionnaires investigating psychological wellbeing. Results reveal that aging influences several timing abilities, from the reproduction of short time intervals to verbal estimations of longer temporal distances. Furthermore, the slowing down of felt passage of time regarding the last few days with age was fully mediated by the intensity of depressive symptoms. Overall, these findings suggest that depressive symptoms may play a pivotal role in age-related temporal processing changes.

Autonomous sensory meridian response is associated with a larger heartbeat-evoked potential amplitude without differences in interoceptive awareness

Autonomous sensory meridian response (ASMR) describes the experience of a pleasant body sensation accompanied by a feeling of well-being and relaxation in response to specific audiovisual stimuli, such as whispers and personal attention. Previous work suggests a relationship between this experience with the processing of affective and body states; however, no research has explored differences in interoception between people experiencing ASMR and those who do not. We hypothesized that the ASMR experience is based on interoception processing. To test this, we assessed group differences across different dimensions of interoception: Interoceptive sensibility (IS), measured using the multidimensional assessment of interoceptive awareness (MAIA); Interoceptive accuracy score (IAS), measured by calculating performance in a heartbeat counting task (HCT), and the electrophysiological index of interoception, the heartbeat evoked potential (HEP), which was calculated during the HCT and an ASMR tingle reporting task (ASMR-TRT). Our results showed that IS and IAS, dimensions requiring conscious awareness, showed no differences between groups. However, HEP amplitude was larger in the ASMR group in both tasks. We concluded that the ASMR experience is based on an unconscious interoceptive mechanism, reflected by HEP, where exteroceptive social-affective stimuli are integrated to represent a body state of positive affective feelings and relaxation, as has been described for affective touch. The relevance of this finding relies on that interoceptive function, body regulation, and emotional/affective experiences are fundamental for well-being, and the relationship between ASMR and interoception opens the way to future research exploring the causal relationship between them and their potential clinical applications.

Patients with Disorders of Consciousness: Are They Nonconscious, Unconscious, or Subconscious? Expanding the Discussion

Unprecedented advancements in the diagnosis and treatment of patients with disorders of consciousness (DoC) have given rise to ethical questions about how to recognize and respect autonomy and a sense of agency of the personhood when those capacities are themselves disordered, as they typically are in patients with DoC. At the intersection of these questions rests the distinction between consciousness and unconsciousness. Indeed, evaluations of consciousness levels and capacity for recovery have a significant impact on decisions regarding whether to discontinue or prolong life-sustaining therapy for DoC patients. However, in the unconsciousness domain, there is the confusing array of terms that are regularly used interchangeably, making it quite challenging to comprehend what unconsciousness is and how it might be empirically grounded. In this opinion paper, we will provide a brief overview of the state of the field of unconsciousness and show how a rapidly evolving electroencephalogram (EEG) neuroimaging technique may offer empirical, theoretical, and practical tools to approach unconsciousness and to improve our ability to distinguish consciousness from unconsciousness and also nonconsciousness with greater precision, particularly in cases that are borderline (as is typical in patients with DoC). Furthermore, we will provide a clear description of three distant notions of (un)consciousness (unconsciousness, nonconsciousness, and subconsciousness) and discuss how they relate to the experiential selfhood which is essential for comprehending the moral significance of what makes life worth living.

Pupillometric evidence for a temporal expectations-based account of persistence under temporal uncertainty

People often quit waiting for delayed rewards when the exact timing of those rewards is uncertain. This behavior often has been attributed to self-control failure. Another possibility is that quitting is the result of a rational decision-making process in the face of uncertainty, based on the decision-maker's expectations about the possible arrival times of the awaited reward. There are forms of temporal expectations (e.g., heavy-tailed) under which the expected time remaining until a reward arrives actually increases as time elapses. In those cases, the rational strategy is to quit waiting when the expected reward is no longer worth the expected time remaining. To arbitrate between the "limited self-control" and "temporal expectations" accounts of persistence, we measured pupil diameter during a persistence task, as a physiological marker of surprise (phasic responses) and effort (pre-decision diameter). Phasic pupil responses were elevated in response to reward receipt. Critically, the extent to which pupils dilated following rewards depended on the delay: people showed larger pupillary surprise responses the more delayed the reward was. This result suggests that people expect the reward less the longer they wait for it-a form of temporal expectations under which limiting persistence is rational. Moreover, predecision pupil diameter before quit events was not associated with how long the participant had been waiting, but rather, depended on how atypical the quit decision was compared with the participant's usual behavior. These data provide physiological evidence for a temporal expectations account of persistence under temporal uncertainty.

Why the clock ticks differently in Parkinson's disease: Insights from motor imagery and resting-state functional magnetic resonance imaging

In Parkinson's disease (PD), an impaired perception of suprasecond time intervals has been reported. From a neurobiological perspective, dopamine is thought to be an important mediator of timing. Nevertheless, it is still unclear whether timing deficits in PD occur mainly in the motor context and are associated with corresponding striatocortical loops. This study attempted to fill this gap by investigating time reproduction in the context of a motor imagery task, and its neurobiological correlates in resting-state networks of basal ganglia substructures in PD. Nineteen PD patients and 10 healthy controls therefore underwent two time reproduction tasks. In a motor imagery task, subjects were asked to walk down a corridor for 10 s and reproduce the time spent walking during motor imagery afterwards. In an auditory task, the subjects had to reproduce an acoustically presented time interval of 10 s. Subsequently, resting-state functional magnetic resonance imaging was performed and voxel-wise regressions were conducted between striatal functional connectivity and performance in the individual task at group level and compared between groups. Patients significantly misjudged the time interval in the motor imagery task and an auditory task in comparison to controls. Seed-to-voxel functional connectivity analysis of basal ganglia substructures revealed a significant association between striatocortical connectivity and motor imagery performance. PD patients showed a different pattern of associated striatocortical connections as indicated by significantly different regression slopes for connections of the right putamen and left caudate nucleus. In accordance with previous findings, our data confirm an impaired time reproduction of suprasecond time intervals in PD patients. Our data imply that deficits in time reproduction tasks are not specific to motor context but reflect a general time reproduction deficit. According to our findings, impaired performance in context of motor imagery is accompanied by a different configuration of striatocortical resting-state networks responsible for timing.

Embodying Consciousness through Interoception and a Balanced Time Perspective

This review presents current research and scientific knowledge in body mind sciences through the lens of interoception, as a representative of the body; and time perspective, as the representative of the mind. This intertwining dichotomy has been a subject of discourse in many fields, all having the common denominator of consciousness. Our aim is to expand on the congruities of these seemingly deconstructed worlds-of science and philosophy, of the body and the mind, to show that the place of consciousness lies in the zone between these two. Being aware of the body in the present moment. We introduce interoception and time perspective, focusing on how interoceptive signals are depicted in autonomic nervous system (ANS) regulation, and how this relates to the concept of a balanced time perspective (BTP), a highly adaptive psychological characteristic. Time perspective and interoception are also reviewed in the case of clinical conditions. We assess findings on interoceptive pathways in the body, finding convergence with balanced time perspective through the neuroanatomical lens. We conclude with findings that both dysregulated interoceptive states and a time perspective disbalance are recognized as defining features of mental disorders, proposing prospective practical therapeutic approaches, as well as implications for further research in the field.

Perceived time expands and contracts within each heartbeat

Perception of passing time can be distorted.¹ Emotional experiences, particularly arousal, can contract or expand experienced duration via their interactions with attentional and sensory processing mechanisms.^2,3 Current models suggest that perceived duration can be encoded from accumulation processes^4,5 and from temporally evolving neural dynamics.^6,7 Yet all neural dynamics and information processing ensue at the backdrop of continuous interoceptive signals originating from within the body. Indeed, phasic fluctuations within the cardiac cycle impact neural and information processing.^{8,9,10,11,12,13,14,15} Here, we show that these momentary cardiac fluctuations distort experienced time and that their effect interacts with subjectively experienced arousal. In a temporal bisection task, durations (200-400 ms) of an emotionally neutral visual shape or auditory tone (experiment 1) or of an image displaying happy or fearful facial expressions (experiment 2) were categorized as short or long.¹⁶ Across both experiments, stimulus presentation was time-locked to systole, when the heart contracts and baroreceptors fire signals to the brain, and to diastole, when the heart relaxes, and baroreceptors are quiescent. When participants judged the duration of emotionally neural stimuli (experiment 1), systole led to temporal contraction, whereas diastole led to temporal expansion. Such cardiac-led distortions were further modulated by the arousal ratings of the perceived facial expressions (experiment 2). At low arousal, systole contracted while diastole expanded time, but as arousal increased, this cardiac-led time distortion disappeared, shifting duration perception toward contraction. Thus, experienced time contracts and expands within each heartbeat-a balance that is disrupted under heightened arousal.

Wrinkles in subsecond time perception are synchronized to the heart

The role of the heart in the experience of time has been long theorized but empirical evidence is scarce. Here, we examined the interaction between fine-grained cardiac dynamics and the momentary experience of subsecond intervals. Participants performed a temporal bisection task for brief tones (80-188 ms) synchronized with the heart. We developed a cardiac Drift-Diffusion Model (cDDM) that embedded contemporaneous heart rate dynamics into the temporal decision model. Results revealed the existence of temporal wrinkles-dilation or contraction of short intervals-in synchrony with cardiac dynamics. A lower prestimulus heart rate was associated with an initial bias in encoding the millisecond-level stimulus duration as longer, consistent with facilitation of sensory intake. Concurrently, a higher prestimulus heart rate aided more consistent and faster temporal judgments through more efficient evidence accumulation. Additionally, a higher speed of poststimulus cardiac deceleration, a bodily marker of attention, was associated with a greater accumulation of sensory temporal evidence in the cDDM. These findings suggest a unique role of cardiac dynamics in the momentary experience of time. Our cDDM framework opens a new methodological avenue for investigating the role of the heart in time perception and perceptual judgment.

Body and Time: Virtual Embodiment and its Effect on Time Perception

This article explores the effect of one's body representation on time perception. Time Perception is modulated by a variety of factors including, e.g., the current situation or activity, it can display significant disturbances caused by psychological disorders, and it is influenced by emotional and interoceptive states, i.e., "the sense of the physiological condition of the body". We investigated this relation between one's own body and the perception of time in a novel Virtual Reality (VR) experiment explicitly fostering user activity. Forty-Eight participants randomly experienced different degrees of embodiment: i) without an avatar (low), ii) with hands (medium), and iii) with a high-quality avatar (high). Participants had to repeatedly activate a virtual lamp and estimate the duration of time intervals as well as judge the passage of time. Our results show a significant effect of embodiment on time perception: time passes slower in the low embodiment condition compared to the medium and high conditions. In contrast to prior work, the study provides missing evidence that this effect is independent of the level of activity of participants: In our task, users were prompted to repeatedly perform body actions, thereby ruling-out a potential influence of the level of activity. Importantly, duration judgements in both the millisecond and minute ranges seemed unaffected by variations in embodiment. Taken together, these results lead to a better understanding of the relationship between the body and time.

Change in Time Perception Following the Place of Pre-Existence Technique

Time perception is closely related to spatial and bodily perception, yet little is known about how this interrelationship is impacted by meditation and biological sex. To examine this, we studied the effects of a stepwise application of three meditation techniques, from focused attention, to open monitoring to non-dual meditation, encompassed in the Place of Pre-Existence technique (PPEt) on the subjective perception of time, space and body using a pre-post research design. A total of 280 participants (mean age = 47.09 years; SD = 10.13; 127:153 males to females) completed the Subjective Time, Self, Space inventory before and after PPEt. Following PPEt, participants perceived time passing as slowing down, while time intensity, relaxation, 'awareness of space' and 'awareness of body' increased, suggesting heightened mindfulness to these constructs following the training. Awareness of space revealed to be modulated by biological sex and meditation expertise, with males showing a decrease of spatial awareness as a function of meditation expertise while females showed an opposite pattern. The speed and intensity of the experience of time both correlated with body and space awareness. In line with previous studies demonstrating a connection between relaxation and perception of time, a significant correlation was found between relaxation and the subjective experience of the intensity of time. The current results are discussed in the context of the embodied experience of time, and the Sphere Model of Consciousness.

Mnemonic Content and Hippocampal Patterns Shape Judgments of Time

Our experience of time can feel dilated or compressed, rather than reflecting true "clock time." Although many contextual factors influence the subjective perception of time, it is unclear how memory accessibility plays a role in constructing our experience of and memory for time. Here, we used a combination of behavioral and functional MRI measures in healthy young adults (N = 147) to ask the question of how memory is incorporated into temporal duration judgments. Behaviorally, we found that event boundaries, which have been shown to disrupt ongoing memory integration processes, result in the temporal compression of duration judgments. Additionally, using a multivoxel pattern similarity analysis of functional MRI data, we found that greater temporal pattern change in the left hippocampus within individual trials was associated with longer duration judgments. Together, these data suggest that mnemonic processes play a role in constructing representations of time.

Temporal scaling of human scalp-recorded potentials

Neural activity is traditionally thought to occur over fixed timescales. However, recent animal work has suggested that some neural responses occur over varying timescales. We extended this animal result to humans by detecting temporally scaled signals noninvasively at the scalp in four different tasks. Our results suggest that temporal scaling is an important feature of cognitive processes known to unfold over varying timescales.

Much of human behavior is governed by common processes that unfold over varying timescales. Standard event-related potential analysis assumes fixed-duration responses relative to experimental events. However, recent single-unit recordings in animals have revealed neural activity scales to span different durations during behaviors demanding flexible timing. Here, we employed a general linear modeling approach using a combination of fixed-duration and variable-duration regressors to unmix fixed-time and scaled-time components in human magneto-/electroencephalography (M/EEG) data. We use this to reveal consistent temporal scaling of human scalp–recorded potentials across four independent electroencephalogram (EEG) datasets, including interval perception, production, prediction, and value-based decision making. Between-trial variation in the temporally scaled response predicts between-trial variation in subject reaction times, demonstrating the relevance of this temporally scaled signal for temporal variation in behavior. Our results provide a general approach for studying flexibly timed behavior in the human brain.

Perceptual confidence of visual stimulus features is associated with duration perception

It has been shown that the perceived duration of an object in the subsecond range is closely associated with its nontemporal perceptual properties, the mechanism under which remains unclear. Previous studies have revealed a modulatory effect of early visual feature processing on the apparent duration. Here, we further examined the relationship between perceptual confidence and subjective time by asking participants to simultaneously perform temporal and nontemporal perceptual judgments. The results revealed a significant effect on confidence levels. When participants' confidence in judging the coherent motion direction or relative dot numerosity increases, their perceived duration of the stimulus also appears longer. These results are discussed in the context of perceptual evidence accumulation and evaluation for the decision-making of perceptual properties. They suggest a profound contribution of object processing to the computation of subjective time and provide further insights into the mechanism of event timing.

Time in schizophrenia: a link between psychopathology, psychophysics and technology

It has been widely demonstrated that time processing is altered in patients with schizophrenia. This perspective review delves into such temporal deficit and highlights its link to low-level sensory alterations, which are often overlooked in rehabilitation protocols for psychosis. However, if temporal impairment at the sensory level is inherent to the disease, new interventions should focus on this dimension. Beyond more traditional types of intervention, here we review the most recent digital technologies for rehabilitation and the most promising ones for sensory training. The overall aim is to synthesise existing literature on time in schizophrenia linking psychopathology, psychophysics, and technology to help future developments.

Mystical Experience

This paper proposes to study mystical experience by contrasting it with “ordinary” experience, i.e., with standard consciousness. It emphasises the construed nature of standard consciousness and the role that the mutual connectedness of mental contents plays in its construction. It then shows that removal of the factors that are responsible for the “making” of standard consciousness accounts for the principal features of mystical experience; these features are, therefore, mainly negative. Understanding mystical experience as the suppression of factors that contribute to the construction of standard consciousness, along with a discussion of the mechanism that makes this possible, permits answers to some frequently asked questions, such as: Why is mystical experience ineffable? What is its epistemic status? Does it have implications for our understanding of mind, consciousness, and self?

Memory for the Future: Psychodynamic Approach to Time and Self Through the Default Network

Time exists in us, and our self exists in time. Our self is affected and shaped by time to the point that a better understanding of the former can aid the understanding of the latter. Psychoanalysis works through self and time, where the self is composed of the biopsychosocial history (the past) of the individual and able to map a trajectory for the future. The psychoanalytic relationship starts from a "measurement": an active process able to alter the system being measured-the self-continuously built over time. This manuscript, starts from the philosophical and scientific tradition of a proximity between time and self, suggesting a neural overlapping at the Default Network. A historical and scientific background will be introduced, proposing a multidisciplinary dimension that has characterized the birth of psychoanalysis (its past), influencing its present and future in the dialogue with physics and neuroscience. After a historical scientific introduction, a neural entanglement between past and future at the Default Network level will be proposed, tracing a link with the self at the level of this network. This hypothesis will be supported by studies in cognitive neurosciences and functional neuroimaging which have used the resting state functional Magnetic Resonance Imaging. The ontogenetic development of time perception will be discussed, consistent with self-development and the Default Network's function. The most common form of dementia, the Alzheimer's Disease, in which the perception of time is brutally impaired together with a loss of the self's functions will be proposed to support this idea. Finally, the potential theoretical and clinical significance for psychoanalysis and psychodynamic neurosciences, will be discussed.

Mindfulness and Nondual Well-Being – What is the Evidence that We Can Stay Happy?

Research into subjective well-being (SWB) focuses on conducive life conditions, healthy cognitive-affective processes and adaptive behaviours, however, in this model, well-being fluctuates based on changing mental and physical phenomena. This inquiry explores the possibility that we can have a nondual experience of well-being that is unaffected by such movements and investigates if the literature supports this. The assertion in traditional mindfulness that the sense of self is constructed and responsible for such fluctuations is explored, along with what evidence there is that mindfulness practices deliver relevant cognitive and behavioural correlates associated with such a way of being. Proposed preconditions include (a) nondual awareness or the perception of no-self; (b) increased positive affect, decreased negative affect, and increased self-lessness; (c) increased capacity to maintain (or protect) well-being including heightened emotional self-regulation and resilience to aversive stimuli. Research findings provide some evidence that the sense of self can be both constructed and deconstructed, and that mindfulness training may target psychological dimensions that could contribute to an experience of well-being that transcends the impact of life conditions. Recommendations are made for a collaborative relationship between SWB research and mindfulness to expand the inquiry into possible causes and conditions of ‘nondual well-being’.

Brain–Heart Interaction and the Experience of Flow While Playing a Video Game

The flow state – an experience of complete absorption in an activity – is linked with less self-referential processing and increased arousal. We used the heart-evoked potential (HEP), an index representing brain–heart interaction, as well as indices of peripheral physiology to assess the state of flow in individuals playing a video game. 22 gamers and 21 non-gamers played the video game Thumper for 25 min while their brain and cardiorespiratory signals were simultaneously recorded. The more participants were absorbed in the game, the less they thought about time and the faster time passed subjectively. On the cortical level, the fronto-central HEP amplitude was significantly lower while playing the game compared to resting states before and after the game, reflecting less self-referential processing while playing. This HEP effect corresponded with lower activity during gameplay in brain regions contributing to interoceptive processing. The HEP amplitude predicted the level of absorption in the game. While the HEP amplitude was overall lower during the gaming session than during the resting states, within the gaming session the amplitude of HEP was positively associated with absorption. Since higher absorption was related to higher performance in the game, the higher HEP in more absorbed individuals reflects more efficient brain–heart interaction, which is necessary for efficient game play. On the physiological level, a higher level of flow was associated with increased overall sympathetic activity and less inhibited parasympathetic activity toward the end of the game. These results are building blocks for future neurophysiological assessments of flow.

Linear vector models of time perception account for saccade and stimulus novelty interactions

Various models (e.g., scalar, state-dependent network, and vector models) have been proposed to explain the global aspects of time perception, but they have not been tested against specific visual phenomena like perisaccadic time compression and novel stimulus time dilation. Here, in two separate experiments (N = 31), we tested how the perceived duration of a novel stimulus is influenced by 1) a simultaneous saccade, in combination with 2) a prior series of repeated stimuli in human participants. This yielded a novel behavioral interaction: pre-saccadic stimulus repetition neutralizes perisaccadic time compression. We then tested these results against simulations of the above models. Our data yielded low correlations against scalar model simulations, high but non-specific correlations for our feedforward neural network, and correlations that were both high and specific for a vector model based on identity of objective and subjective time. These results demonstrate the power of global time perception models in explaining disparate empirical phenomena and suggest that subjective time has a similar essence to time's physical vector.

Sub- and Supra-Second Timing in Auditory Perception: Evidence for Cross-Domain Relationships

Previous studies indicate that there are at least two levels of temporal processing: the sub- and supra-second domains. The relationship between these domains remains unclear. The aim of this study was to test whether performance on the sub-second level is related to that on the supra-second one, or whether these two domains operate independently. Participants were 118 healthy adults (mean age = 23 years). The sub-second level was studied with a temporal-order judgment task and indexed by the Temporal Order Threshold (TOT), on which lower values corresponded to better performance. On the basis of TOT results, the initial sample was classified into two groups characterized by either higher temporal efficiency (HTE) or lower temporal efficiency (LTE). Next, the efficiency of performance on the supra-second level was studied in these two groups using the subjective accentuation task, in which participants listened to monotonous sequences of beats and were asked to mentally accentuate every n-th beat to create individual rhythmic patterns. The extent of temporal integration was assessed on the basis of the number of beats being united and better performance corresponded to longer units. The novel results are differences between groups in this temporal integration. The HTE group integrated beats in significantly longer units than did the LTE group. Moreover, for tasks with higher mental load, the HTE group relied more on a constant time strategy, whereas the LTE group relied more on mental counting, probably because of less efficient temporal integration. These findings provide insight into associations between sub- and supra-second levels of processing and point to a common time keeping system, which is active independently of temporal domain.

Neural substrates of accurate perception of time duration: A functional magnetic resonance imaging study

Time duration, an essential feature of the physical world, is perceived and cognitively interpreted subjectively. While this perception is deeply connected with arousal and interoceptive signals, the underlying neural mechanisms remain elusive. As the insula is critical for integrating information from the external world with the organism's inner state, we hypothesized that it might have a central role in the perception of time duration and contribute to its estimation accuracy. We conducted a functional magnetic resonance imaging study with 27 healthy participants performing temporal duration and pitch bisection tasks that used the same stimuli. By comparison with two referents with short and long duration in the time range of 1 s (close to the heart rate period), or low and high pitch, participants had to decide whether target stimuli were closer in duration or pitch to the referent stimuli. The temporal bisection point between short and long duration perception was obtained through a psychometric response curve analysis for each participant. The deviation between the bisection point and the average of reference stimuli durations was used as a marker of duration accuracy. Duration discrimination-specific activation, contrasted to pitch discrimination, was found in the dorsomedial prefrontal cortex, bilateral cerebellum, and right anterior insular cortex (AIC), extending to the inferior frontal gyrus (IFG), inferior parietal lobule, and frontal pole. The activity in the right AIC and IFG was positively correlated with the accuracy of duration discrimination. The right AIC is known to be related to the reproduction of duration, whereas the right IFG is involved in categorical decisions. Thus, the comparison between the referent durations reproduced in the AIC and the target duration may occur in the right IFG. We conclude that the right AIC and IFG contribute to the accurate perception of temporal duration.

Unpredictable fearful stimuli disrupt timing activities: Evidence from event-related potentials

The present study investigated the effect of an imminent fearful stimulus on an ongoing temporal task. Participants judged the duration of a blank temporal interval followed by a fearful or a neutral image. Results showed an underestimation of the duration in the fearful condition relative to the neutral condition, but only when the occurrence of the fearful image was difficult to predict. ERPs results for the blank temporal interval found no effect of the fearful stimulus on the contingent negative variation (CNV) amplitude in the clock stage. However, after the image onset, there was a larger P1 for the fearful relative to the neutral condition. Although this effect was indistinguishable regardless of whether the fearful event could be easily predicted, a late positive potential (LPP) component displayed larger amplitude only for unpredictable fearful stimuli. The time-frequency results showed enhanced delta-theta power (0.5-7.5 Hz) for the unpredictable fearful stimuli in the late stage. Importantly, the enhanced delta-theta rhythm correlated negatively with the duration judgments. Together, these results suggest that an unpredictable fearful event might divert more attention away from the counting process in the working memory stage, resulting in missing ticks and temporal underestimation.

Perception of Happening: How the Brain Deals with the No-History Problem

In physics, the temporal dimension has units of infinitesimally brief duration. Given this, how is it possible to perceive things, such as motion, music, and vibrotactile stimulation, that involve extension across many units of time? To address this problem, it is proposed that there is what is termed an "information construct of happening" (ICOH), a simultaneous representation of recent, temporally differentiated perceptual information on the millisecond time scale. The main features of the ICOH are (i) time marking, semantic labeling of all information in the ICOH with ordinal temporal information and distance from what is informationally identified as the present moment, (ii) vector informational features that specify kind, direction, and rate of change for every feature in a percept, and (iii) connectives, information relating vector informational features at adjacent temporal locations in the ICOH. The ICOH integrates products of perceptual processing with recent historical information in sensory memory on the subsecond time scale. Perceptual information about happening in informational sensory memory is encoded in semantic form that preserves connected semantic trails of vector and timing information. The basic properties of the ICOH must be supported by a general and widespread timing mechanism that generates ordinal and interval timing information and it is suggested that state-dependent networks may suffice for that purpose. Happening, therefore, is perceived at a moment and is constituted by an information structure of connected recent historical information.

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.