The context of temporal processing is represented in the multidimensional relationships between timing tasks

In the present study we determined the performance interrelations of ten different tasks that involved the processing of temporal intervals in the subsecond range, using multidimensional analyses. Twenty human subjects executed the following explicit timing tasks: interval categorization and discrimination (perceptual tasks), and single and multiple interval tapping (production tasks). In addition, the subjects performed a continuous circle-drawing task that has been considered an implicit timing paradigm, since time is an emergent property of the produced spatial trajectory. All tasks could be also classified as single or multiple interval paradigms. Auditory or visual markers were used to define the intervals. Performance variability, a measure that reflects the temporal and non-temporal processes for each task, was used to construct a dissimilarity matrix that quantifies the distances between pairs of tasks. Hierarchical clustering and multidimensional scaling were carried out on the dissimilarity matrix, and the results showed a prominent segregation of explicit and implicit timing tasks, and a clear grouping between single and multiple interval paradigms. In contrast, other variables such as the marker modality were not as crucial to explain the performance between tasks. Thus, using this methodology we revealed a probable functional arrangement of neural systems engaged during different timing behaviors.     

Dissociating explicit timing from temporal expectation with fMRI

Explicit timing is engaged whenever subjects make a deliberate estimate of discrete duration in order to compare it with a previously memorised standard. Conversely, implicit timing is engaged, even without a specific instruction to time, whenever sensorimotor information is temporally structured and can be used to predict the duration of future events. Both emergent timing (motor) and temporal expectation (perceptual) are forms of implicit timing. Recent fMRI studies demonstrate discrete neural substrates for explicit and implicit timing. Specifically, basal ganglia are activated almost invariably by explicit timing, with co-activation of prefrontal, premotor and cerebellar areas being more context-dependent. Conversely, implicit perceptual timing (or "temporal expectation") recruits cortical action circuits, comprising inferior parietal and premotor areas, highlighting its role in the optimisation of prospective behaviour.     

Tracking of food quantity by coyotes (Canis latrans)

Previous studies have demonstrated that Weber's Law mediates quantitative discrimination abilities across various species. Here, we tested coyotes’ (Canis latrans) ability to discriminate between various quantities of food and investigated whether this ability conforms to predictions of Weber's Law. We demonstrate herein that coyotes are capable of reliably discriminating large versus small quantities of discrete food items. As predicted by Weber's Law, coyotes’ quantitative discrimination abilities are mediated by the ratio between the large and small quantities of food and exhibit scalar variability. Furthermore, in this task coyotes were not discriminating large versus small quantities based on olfactory cues alone.     

Counting in a time discrimination task in children and adults

The present study investigated in 5- and 8-year-olds, as well as in adults, the effect of verbal counting on temporal discrimination behavior in a generalization task with two duration ranges in order to test the scalar timing property. The results showed that counting improved temporal sensitivity in all age groups, although sensitivity to time remained lower in the younger children. Furthermore, in the 5-year-olds, the temporal generalization behavior conformed well to the scalar property of variance both in the counting and the non-counting condition. However, this conformity to the scalar timing property disappeared when counting was used in the 8-year-olds and the adults. The development of the ability to count time at a constant rhythm is discussed as the major reason for this departure of temporal behavior from the scalar property of variance when counting is employed.     

Relative timing: from behaviour to neurons

Processing of temporal information is critical to behaviour. Here, we review the phenomenology and mechanism of relative timing, ordinal comparisons between the timing of occurrence of events. Relative timing can be an implicit component of particular brain computations or can be an explicit, conscious judgement. Psychophysical measurements of explicit relative timing have revealed clues about the interaction of sensory signals in the brain as well as in the influence of internal states, such as attention, on those interactions. Evidence from human neurophysiological and functional imaging studies, neuropsychological examination in brain-lesioned patients, and temporary disruptive interventions such as transcranial magnetic stimulation (TMS), point to a role of the parietal cortex in relative timing. Relative timing has traditionally been modelled as a ‘race’ between competing neural signals. We propose an updated race process based on the integration of sensory evidence towards a decision threshold rather than simple signal propagation. The model suggests a general approach for identifying brain regions involved in relative timing, based on looking for trial-by-trial correlations between neural activity and temporal order judgements (TOJs). Finally, we show how the paradigm can be used to reveal signals related to TOJs in parietal cortex of monkeys trained in a TOJ task.     

The failure of Weber's law in time perception and production

Weber's law--constancy of the coefficient of variation--is an apparently ubiquitous feature of time perception, and forms the foundation of several theories of timing. We sought evidence for Weber's law in temporal production and categorization experiments. The production task required pigeons to switch between keys within a specified temporal window. The categorization task required them to classify a stimulus duration as either short or long. Weber fractions did not descend to a horizontal asymptote, but were U-shaped: they decreased as a function of target duration, and increased again at intermediate and long durations. This pattern conforms neither to Weber's law, nor to its generalized form (Getty, D.J., 1975. Discrimination of short temporal intervals: a comparison of two models. Percept. Psychophys. 18, 1-8). A model of counter failure accommodated the U-shaped pattern.     

The Cerebellum Predicts the Temporal Consequences of Observed Motor Acts

It is increasingly clear that we extract patterns of temporal regularity between events to optimize information processing. The ability to extract temporal patterns and regularity of events is referred as temporal expectation. Temporal expectation activates the same cerebral network usually engaged in action selection, comprising cerebellum. However, it is unclear whether the cerebellum is directly involved in temporal expectation, when timing information is processed to make predictions on the outcome of a motor act. Healthy volunteers received one session of either active (inhibitory, 1Hz) or sham repetitive transcranial magnetic stimulation covering the right lateral cerebellum prior the execution of a temporal expectation task. Subjects were asked to predict the end of a visually perceived human body motion (right hand handwriting) and of an inanimate object motion (a moving circle reaching a target). Videos representing movements were shown in full; the actual tasks consisted of watching the same videos, but interrupted after a variable interval from its onset by a dark interval of variable duration. During the ‘dark’ interval, subjects were asked to indicate when the movement represented in the video reached its end by clicking on the spacebar of the keyboard. Performance on the timing task was analyzed measuring the absolute value of timing error, the coefficient of variability and the percentage of anticipation responses. The active group exhibited greater absolute timing error compared with the sham group only in the human body motion task. Our findings suggest that the cerebellum is engaged in cognitive and perceptual domains that are strictly connected to motor control.     

Large Scale Brain Functional Networks Support Sentence Comprehension: Evidence from Both Explicit and Implicit Language Tasks

Previous studies have indicated that sentences are comprehended via widespread brain regions in the fronto-temporo-parietal network in explicit language tasks (e.g., semantic congruency judgment tasks), and through restricted temporal or frontal regions in implicit language tasks (e.g., font size judgment tasks). This discrepancy has raised questions regarding a common network for sentence comprehension that acts regardless of task effect and whether different tasks modulate network properties. To this end, we constructed brain functional networks based on 27 subjects’ fMRI data that was collected while performing explicit and implicit language tasks. We found that network properties and network hubs corresponding to the implicit language task were similar to those associated with the explicit language task. We also found common hubs in occipital, temporal and frontal regions in both tasks. Compared with the implicit language task, the explicit language task resulted in greater global efficiency and increased integrated betweenness centrality of the left inferior frontal gyrus, which is a key region related to sentence comprehension. These results suggest that brain functional networks support both explicit and implicit sentence comprehension; in addition, these two types of language tasks may modulate the properties of brain functional networks.     

Unequal interval time-place learning

In time-place learning tasks food availability depends upon both spatial and temporal variables. For example, food might be first available at location one, then location two, then location three, and finally location four. To date, the duration of food availability at each of the locations have been identical (e.g. for 4 min). The major purpose of the present experiment was to determine if rats can successfully learn a time-place task in which four locations provided food for different durations. Lever 1 intermittently produced food for 6 min, then Lever 2 produced food for 4 min. Lever 3 and 4 provided food for 2 and 8 min, respectively. Rats were able to learn this unequal interval time-place task. However, their behavior on this unequal interval time-place task was not in agreement with Scalar Expectancy Theory/Weber's Law.     

Interrupting timing in interval production and discrimination: similarities and differences

Interruptions in human timing have been studied in the last few years using temporal production and discrimination tasks. Expecting a break shortened perceived duration in both paradigms but manipulating break duration affected time production only, suggesting that preparatory processes might not take place in time discrimination. In time production, using cues revealed that providing information about the break may modulate the effect of break expectancy. For example, time was perceived as shorter when a break was expected in trials with no breaks, but forewarning participants of the break absence with a cue almost abolished the effect. In the present experiment, a tone was classified as "short" or "long" in a discrimination task. Location and duration of breaks were varied and cues were provided in some trials with no breaks. Results showed an effect of break expectancy: perceived duration shortened with increasing pre-break duration. Reducing expectancy with cues in uninterrupted tones decreased the proportion of "short" responses in long-tone trials, but not in short-tone trials. As in previous discrimination experiments, perceived duration was unaffected by varying break duration. Similarities and differences in results as well as in their interpretation when breaks are used in time production and time discrimination tasks are discussed.     

Do rats represent time logarithmically or linearly?

This study examined two possible psychophysical time scales, a logarithmic representation of time with constant variability and a linear representation of time with scalar variability. Twenty-four rats were tested on a modified temporal bisection procedure in which multiple responses could occur in a 10-s time window after the termination of a stimulus. The number of “long” or “short” responses was used as a measure of the rats’ certainty of the duration of the presented interval. Data were analyzed with signal detection theory, and straight lines were fit to the zROC curves with the assumptions of a logarithmic representation of time with constant variability and a linear representation of time with scalar variability. The logarithmic representation of time with constant variability provided a better fit to the data than the linear representation of time with scalar variability.     

Influence of the interstimulus interval on temporal processing and learning: testing the state-dependent network model

The ability to determine the interval and duration of sensory events is fundamental to most forms of sensory processing, including speech and music perception. Recent experimental data support the notion that different mechanisms underlie temporal processing in the subsecond and suprasecond range. Here, we examine the predictions of one class of subsecond timing models: state-dependent networks. We establish that the interval between the comparison and the test interval, interstimulus interval (ISI), in a two-interval forced-choice discrimination task, alters the accuracy of interval discrimination but not the point of subjective equality—i.e. while timing was impaired, subjective time contraction or expansion was not observed. We also examined whether the deficit in temporal processing produced by short ISIs can be reduced by learning, and determined the generalization patterns. These results show that training subjects on a task using a short or long ISI produces dramatically different generalization patterns, suggesting different forms of perceptual learning are being engaged. Together, our results are consistent with the notion that timing in the range of hundreds of milliseconds is local as opposed to centralized, and that rapid stimulus presentation rates impair temporal discrimination. This interference is, however, decreased if the stimuli are presented to different sensory channels.     

The role of superior temporal cortex in auditory timing

Recently, there has been upsurge of interest in the neural mechanisms of time perception. A central question is whether the representation of time is distributed over brain regions as a function of stimulus modality, task and length of the duration used or whether it is centralized in a single specific and supramodal network. The answers seem to be converging on the former, and many areas not primarily considered as temporal processing areas remain to be investigated in the temporal domain. Here we asked whether the superior temporal gyrus, an auditory modality specific area, is involved in processing of auditory timing. Repetitive transcranial magnetic stimulation was applied over left and right superior temporal gyri while participants performed either a temporal or a frequency discrimination task of single tones. A significant decrease in performance accuracy was observed after stimulation of the right superior temporal gyrus, in addition to an increase in response uncertainty as measured by the Just Noticeable Difference. The results are specific to auditory temporal processing and performance on the frequency task was not affected. Our results further support the idea of distributed temporal processing and speak in favor of the existence of modality specific temporal regions in the human brain.     

Speed-accuracy tradeoff in olfaction

The basic psychophysical principle of speed-accuracy tradeoff (SAT) has been used to understand key aspects of neuronal information processing in vision and audition, but the principle of SAT is still debated in olfaction. In this study we present the direct observation of SAT in olfaction. We developed a behavioral paradigm for mice in which both the duration of odorant sampling and the difficulty of the odor discrimination task were controlled by the experimenter. We observed that the accuracy of odor discrimination increases with the duration of imposed odorant sampling, and that the rate of this increase is slower for harder tasks. We also present a unifying picture of two previous, seemingly disparate experiments on timing of odorant sampling in odor discrimination tasks. The presence of SAT in olfaction provides strong evidence for temporal integration in olfaction and puts a constraint on models of olfactory processing.     

A neurocomputational model for optimal temporal processing

Humans can estimate the duration of intervals of time, and psychophysical experiments show that these estimations are subject to timing errors. According to standard theories of timing, these errors increase linearly with the interval to be estimated (Weber's law), and both at longer and shorter intervals, deviations from linearity are reported. This is not easily reconciled with the accumulation of neuronal noise, which would only lead to an increase with the square root of the interval. Here, we offer a neuronal model which explains the form of the error function as a result of a constrained optimization process. The model consists of a number of synfire chains with different transmission times, which project onto a set of readout neurons. We show that an increase in the transmission time corresponds to a superlinear increase of the timing errors. Under the assumption of a fixed chain length, the experimentally observed error function emerges from optimal selection of chains for each given interval. Furthermore, we show how this optimal selection could be implemented by competitive spike-timing dependent plasticity in the connections from the chains to the readout network, and discuss implications of our model on selective temporal learning and possible neural architectures of interval timing.     

Dissociable Neural Systems for Timing: Evidence from Subjects with Basal Ganglia Lesions

Background

The neural basis of timing remains poorly understood. Although controversy persists, many lines of evidence, including studies in animals, functional imaging studies in humans and lesion studies in humans and animals suggest that the basal ganglia are important for temporal processing [1].

Methodology/Principal Findings

We report data from a wide range of timing tasks from two subjects with disabling neurologic deficits caused by bilateral lesions of the basal ganglia. Both subjects perform well on tasks assessing time estimation, reproduction and production tasks. Additionally, one subject performed normally on psychophysical tasks requiring the comparison of time intervals ranging from milliseconds to seconds; the second subject performed abnormally on the psychophysical task with a 300ms standard but did well with 600ms, 2000ms and 8000ms standards. Both subjects performed poorly on an isochronous rhythm production task on which they are required to maintain rhythmic tapping.

Conclusions/Significance

As studies of subjects with brain lesions permit strong inferences regarding the necessity of brain structures, these data demonstrate that the basal ganglia are not crucial for many sub- or supra-second timing operations in humans but are needed for the timing procedures that underlie the production of movements. This dissociation suggests that distinct and dissociable processes may be employed to measure time intervals. Inconsistencies in findings regarding the neural basis of timing may reflect the availability of multiple temporal processing routines that are flexibly implemented in response to task demands.     

Manipulating decision processes in the human scalar timing system

Two experiments attempted to manipulate the decision processes used in a temporal generalisation task with humans. In Experiment 1, payoffs (points awarded or deducted) were used to try to alter behaviour when the standard duration was 400ms, and the comparison durations ranged from 100 to 700ms in 100ms steps. Two conditions which either encouraged or discouraged the subject to identify a comparison duration as the standard were compared with a neutral condition. Encouraging identifications of the standard increased the proportion of identifications of the standard, whereas the discouraging manipulation had more ambiguous effects. Using the "modified Church and Gibbon" model, it was shown that the effect of the encourage manipulation was an increase in the response threshold, consistent with the information-processing version of scalar timing theory. A second experiment compared encourage and discourage manipulations with a more difficult discrimination (comparison durations spaced in 50ms steps around the 400ms standard), and with more distinct payoff differences for the different conditions. Behavioural effects were much more marked in Experiment 2, with the encourage condition producing more identifications of a comparison duration as the standard for all comparison durations except the shortest, compared with the discourage condition. Modelling showed that the main theoretical difference between the two conditions was in a change in the response threshold, in a manner consistent with the scalar timing model.     

Pigeons' timing of an arbitrary and a naturalistic auditory stimulus: tone versus cooing

Previous animal research has traditionally used arbitrary stimuli to investigate timing in a temporal bisection procedure. The current study compared the timing of the duration of an arbitrary, auditory stimulus (a 500-Hz tone) to the timing of the duration of a naturalistic, auditory stimulus (a pigeon cooing). In the first phase of this study, temporal perception was assessed by comparing psychophysical functions for the duration of tone and cooing signals. In the first set of tests, the point of subjective equality (PSE) was significantly lower for the tone than for the cooing stimulus, indicating that tones were judged longer than equivalent durations of cooing. In the second set of tests, gaps were introduced in the tone signal to match those present in the cooing signal, and no significant difference in the PSE for the tone or the cooing signal was found. A repetition of the testing conducted with gaps removed from the tone signal, failed to replicate the difference in the PSEs for the tone and cooing signals originally obtained. In the second phase of the study, memory for the duration of tone and cooing was examined, and a choose-long bias was found for both signals. Based on these results, it appears that, for pigeons, there may be no significant differences in either temporal perception or temporal memory for arbitrary, auditory signals and more complex, naturalistic, auditory signals.     

Prospective timing under dual-task paradigms: attentional and contextual-change mechanisms

The effect of a concurrent memory task on prospective time estimates by human participants was investigated in two experiments. The objective was to isolate task effects from those of participant timing strategy (self-paced counting) and number of contextual changes during the temporal stimulus. Accordingly, self-paced counting was suppressed by requiring participants to perform a word-reading task during the temporal stimuli, while number of stimulus changes presented during temporal stimuli was controlled. Presence versus absence of the concurrent memory task was manipulated in Experiment 1, and instruction to focus on timing or to focus on memory was manipulated in Experiment 2. There was no significant effect of presence versus absence of the concurrent memory task on time estimates; however, time estimates were shorter when participants were instructed to focus on memory versus timing. In both experiments, time estimates were positively correlated with participants' estimates of the number of words presented during the interval, even though number of words presented was invariant. These findings were generally consistent with resource-allocation attentional accounts of concurrent task effects; however, support for a contextual-change model of timing was also obtained.