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Time is a universal psychological dimension, but time perception has often been studied and discussed in relative isolation. Increasingly, researchers are searching for unifying principles and integrated models that link time perception to other domains. In this review, we survey the links between temporal cognition and other psychological processes. Specifically, we describe how subjective duration is affected by nontemporal stimulus properties (perception), the allocation of processing resources (attention), and past experience with the stimulus (memory). We show that many of these connections instantiate a "processing principle," according to which perceived time is positively related to perceptual vividity and the ease of extracting information from the stimulus. This empirical generalization generates testable predictions and provides a starting-point for integrated theoretical frameworks. By outlining some of the links between temporal cognition and other domains, and by providing a unifying principle for understanding these effects, we hope to encourage time-perception researchers to situate their work within broader theoretical frameworks, and that researchers from other fields will be inspired to apply their insights, techniques, and theorizing to improve our understanding of the representation and judgment of time. (PsycINFO Database Record, ((c) 2016 APA, all rights reserved).)

Variations in both pitch and time are important in conveying meaning through speech and music, however, research is scant on perceptual interactions between these two domains. Using an ordinal comparison procedure, we explored how different pitch levels of flanker tones influenced the perceived duration of empty interstimulus intervals (ISIs). Participants heard monotonic, isochronous tone sequences (ISIs of 300, 600, or 1200 ms) composed of either one or five standard ISIs flanked by 500 Hz tones, followed by a final interval (FI) flanked by tones of either the same (500 Hz), higher (625 Hz), or lower (400 Hz) pitch. The FI varied in duration around the standard ISI duration. Participants were asked to determine if the FI was longer or shorter in duration than the preceding intervals. We found that an increase in FI flanker tone pitch level led to the underestimation of FI durations while a decrease in FI flanker tone pitch led to the overestimation of FI durations. The magnitude of these pitch-level effects decreased as the duration of the standard interval was increased, suggesting that the effect was driven by differences in mode-switch latencies to start/stop timing. Temporal context (One vs. Five Standard ISIs) did not have a consistent effect on performance. We propose that the interaction between pitch and time may have important consequences in understanding the ways in which meaning and emotion are communicated., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Humans share with other animals an ability to measure the passage of physical time and subjectively experience a sense of time passing. Subjective time has hallmark qualities, akin to other senses, which can be accounted for by formal, psychological, and neurobiological models of the internal clock. These include first-order principles, such as changes in clock speed and how temporal memories are stored, and second-order principles, including timescale invariance, multisensory integration, rhythmical structure, and attentional time-sharing. Within these principles there are both typical individual differences--influences of emotionality, thought speed, and psychoactive drugs--and atypical differences in individuals affected with certain clinical disorders (e.g., autism, Parkinson's disease, and schizophrenia). This review summarizes recent behavioral and neurobiological findings and provides a theoretical framework for considering how changes in the properties of the internal clock impact time perception and other psychological domains.

Healthy volunteers were tested on 7-s and 17-s peak-interval timing procedures following d-amphetamine (20mg-oral), haloperidol (2mg-oral), and placebo treatments in order to assess the dopaminergic regulation of temporal processing. Individual differences were observed in the drug effects such that two different patterns of timing behavior emerged. In the first pattern, d-amphetamine produced proportional leftward shifts of the timing functions while haloperidol produced proportional rightward shifts. This symmetrical pattern of results suggests that clock speed is regulated by the effective level of dopamine, i.e., d-amphetamine increases clock speed and haloperidol decreases clock speed. The second pattern was the opposite of the first pattern and was revealed by d-amphetamine producing proportional rightward shifts of the timing functions while haloperidol produced no reliable effect. This asymmetrical pattern of results is consistent with an explanation in which attention toward the stimulant-induced euphoria produced by d-amphetamine diminishes the attentional resources available for temporal processing, thereby diluting any drug-induced changes in clock speed. The result of increased competition and time-sharing between these two dimensions (e.g., attention towards feelings of euphoria versus attention towards the passage of time) leads to the underestimation/overproduction of temporal intervals. Interestingly, participants that displayed the 'clock-speed' pattern liked d-amphetamine significantly less than participants that displayed the 'attention' pattern and were more variable in a simple reaction time task than other participants. These results suggest that individuals with a higher degree of sensitivity to time are also more sensitive to their feelings of stimulant-induced euphoria and drug liking-suggesting that internal clock and reward pathways share common dopaminergic pathways., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

The perception of time is heavily influenced by attention and memory, both of which change over the lifespan. In the current study, children (8 yrs), young adults (18-25 yrs), and older adults (60-75 yrs) were tested on a duration bisection procedure using 3 and 6-s auditory and visual signals as anchor durations. During test, participants were exposed to a range of intermediate durations, and the task was to indicate whether test durations were closer to the "short" or "long" anchor. All groups reproduced the classic finding that "sounds are judged longer than lights". This effect was greater for older adults and children than for young adults, but for different reasons. Replicating previous results, older adults made similar auditory judgments as young adults, but underestimated the duration of visual test stimuli. Children showed the opposite pattern, with similar visual judgments as young adults but overestimation of auditory stimuli. Psychometric functions were analyzed using the Sample Known Exactly-Mixed Memory quantitative model of the Scalar Timing Theory of interval timing. Results indicate that children show an auditory-specific deficit in reference memory for the anchors, rather than a general bias to overestimate time and that aged adults show an exaggerated tendency to judge visual stimuli as "short" due to a reduction in the availability of controlled attention., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Individuals time as if using a stopwatch that can be stopped or reset on command. Here, we review behavioural and neurobiological data supporting the time-sharing hypothesis that perceived time depends on the attentional and memory resources allocated to the timing process. Neuroimaging studies in humans suggest that timekeeping tasks engage brain circuits typically involved in attention and working memory. Behavioural, pharmacological, lesion and electrophysiological studies in lower animals support this time-sharing hypothesis. When subjects attend to a second task, or when intruder events are presented, estimated durations are shorter, presumably due to resources being taken away from timing. Here, we extend the time-sharing hypothesis by proposing that resource reallocation is proportional to the perceived contrast, both in temporal and non-temporal features, between intruders and the timed events. New findings support this extension by showing that the effect of an intruder event is dependent on the relative duration of the intruder to the intertrial interval. The conclusion is that the brain circuits engaged by timekeeping comprise not only those primarily involved in time accumulation, but also those involved in the maintenance of attentional and memory resources for timing, and in the monitoring and reallocation of those resources among tasks.

In two experiments, the peak-interval procedure was used with humans to test effects related to gaps in multisecond timing. In Experiment 1, peak times of response distributions were shorter when the gap occurred later during the encoding of the criterion time to be reproduced, suggesting that gap expectancy shortened perceived durations. Peak times were also positively related to objective target durations. Spreads of response distributions were generally related to estimated durations. In Experiment 2, peak times were shortest when gaps were expected but did not occur, confirming that the shortening effect of gap expectancy is independent of the gap occurrence. High positive start-stop correlations and moderate positive peak-time-spread correlations showed strong memory variability, whereas low and negative start-spread correlations suggest small response-threshold variability. Correlations seemed not to be influenced by expectancy. Overall, the peak-interval procedure with gaps provided relevant information on similarities and differences in timing in humans and other animals.

Our sense of time is altered by our emotions to such an extent that time seems to fly when we are having fun and drags when we are bored. Recent studies using standardized emotional material provide a unique opportunity for understanding the neurocognitive mechanisms that underlie the effects of emotion on timing and time perception in the milliseconds-to-hours range. We outline how these new findings can be explained within the framework of internal-clock models and describe how emotional arousal and valence interact to produce both increases and decreases in attentional time sharing and clock speed. The study of time and emotion is at a crossroads, and we outline possible examples for future directions.

The cognitive and emotional effects of amygdala or frontal cortex lesions were compared in rats trained to time both a 50-s visual signal paired with food and an embedded 10- or 20-s auditory signal that was paired with either appetitive (food) or aversive (footshock) outcomes. When both auditory and visual signals were paired with food, control and amygdalar-lesioned rats were able to divide attention and to time both signals simultaneously, whereas when the embedded auditory signal was paired with footshock, control rats were impaired in their ability to divide attention and were able to time only one signal at a time. In contrast, amygdalar inactivation blocked this fear-related impairment and allowed rats to time both signals simultaneously, whereas rats with frontal cortex lesions demonstrated sequential processing under all conditions. These results support the proposal that the frontal cortex exerts executive control over the allocation of attentional resources, but that under stressful conditions the amygdala is crucial for the emergence of fear-evoked increments in selective attention leading to deficits in the ability to time 2 or more signals simultaneously., (((c) 2007 APA, all rights reserved).)

In a series of three experiments, simple reaction time (RT) was characterized with respect to a variable preparatory interval (PI) in order to investigate the relationship between interval timing and RT. In Experiment 1, it was shown that RT decreases as a function of PI and that this effect varies with amount of training. In Experiment 2, RT was shown to increase during probe trials that used a novel 6.25s PI, suggesting that the specific durations of the PIs encoded during initial training contribute to the PI effect on RT. In Experiment 3, 100 microg/kg i.p. of raclopride proportionally slowed RT as a function of the PI. These results are discussed within the context of neuropsychological models of interval timing and support an underlying role for cortico-striatal dopaminergic function in temporal processing and simple RT measurements.

Gaps and distracters were presented during the timed signal to examine whether the stop/reset mechanism is activated by (a) changes in the timed signal (switch hypothesis), (b) ITI-like events (ambiguity hypothesis), or (c) processes concurrent with the timing process (time-sharing hypothesis). While the switch and ambiguity hypotheses predict that rats should time through (ignore) distracters, the time-sharing hypothesis predicts that extraneous events (e.g., gaps and distracters) delay timing by causing working memory to decay in proportion to the events' salience. The authors found that response functions were displaced by both gaps and distracters, in accord with the time-sharing hypothesis. Computer simulations show that the time-sharing and memory-decay hypotheses can mechanistically address present data, and reflect different levels of the same model.

Four hypotheses (switch, instructional-ambiguity, memory decay, and time sharing) were evaluated in a reversed peak-interval procedure with gaps by presenting distracter stimuli during the uninterrupted timed signal. The switch, instructional-ambiguity, and memory-decay hypotheses predict that subjects should time through the distracter and delay responding during gaps. The time-sharing hypothesis assumes that the internal clock shares attentional and working-memory resources with other processes, so that both gaps and distracters delay timing by causing working memory to decay. We found that response functions were displaced both by gaps and by distracters. Computer simulations show that when combined, the memory-decay and time-sharing hypotheses can mechanistically address present data, suggesting that these two hypotheses may reflect different levels of analysis of the same phenomenon.

A duration-bisection procedure was used to study the effects of signal modality and divided attention on duration classification in participants at high genetic risk for schizophrenia (HrSz), major affective disorder (HrAff), and normal controls (NC). Participants learned short and long target durations during training and classified probe durations during test. All groups classified visual signals as shorter than equivalent duration auditory signals. However, the difference between auditory and visual signal classification was significantly larger for the HrSz group than for the NC group. We posit a model in which there is a clock rate difference between auditory and visual signals due to an attentional effect at the level of a mode switch that gates pulses into an accumulator. This attentionally mediated clock rate difference was larger for the HrSz participants than for the NC participants, resulting in a larger auditory/visual difference for the HrSz group.

The authors hypothesized that during a gap in a timed signal, the time accumulated during the pregap interval decays at a rate proportional to the perceived salience of the gap, influenced by sensory acuity and signal intensity. When timing visual signals, albino (Sprague-Dawley) rats, which have poor visual acuity, stopped timing irrespective of gap duration, whereas pigmented (Long-Evans) rats, which have good visual acuity, stopped timing for short gaps but reset timing for long gaps. Pigmented rats stopped timing during a gap in a low-intensity visual signal and reset after a gap in a high-intensity visual signal, suggesting that memory for time in the gap procedure varies with the perceived salience of the gap, possibly through an attentional mechanism., (Copyright 2005 APA.)

A growing body of research supports the view that choline is an essential nutrient during early development that has long-lasting effects on memory and attentional processes throughout the lifespan. This review describes the known effects of alterations in dietary choline availability both in adulthood and during early development. Although modest effects of choline on cognitive processes have been reported when choline is administered to adult animals, we have found that the perinatal period is a critical time for cholinergic organization of brain function. Choline supplementation during this period increases memory capacity and precision of the young adult and appears to prevent age-related memory and attentional decline. Deprivation of choline during early development leads to compromised cognitive function and increased decline with age. We propose that this organizational effect of choline availability may be due to relatively permanent alterations in the functioning of the cholinergic synapse, which we have called 'metabolic imprinting'.

The ability of organisms to time and coordinate temporal sequences of events and to select particular aspects of their internal and external environments to which they will attend is vital to the organism's ability to adapt to the world around them. Numerous psychological theories have been proposed that describe how organisms might accomplish such stimulus selection and represent discrete temporal events as well as rhythm production. In addition, a large number of studies have demonstrated that damage to the frontostriatal circuitry appears to compromise the ability of organisms to successfully shift attention and behavior to adapt to changing temporal contexts. This suggests that frontostriatal circuitry is involved in the ability to make such shifts and to process temporal intervals. A selective review is accomplished in this article which focuses upon the specific neural mechanisms that may be involved in interval timing and set shifting. It is concluded that prefrontal cortex, substantia nigra pars compacta, pedunculopontine nucleus, and the direct and indirect pathways from the caudate to the thalamus may provide the neuroanatomical and neurophysiological substrates that underlie the organism's ability to shift its attention from one temporal context to another., (Copyright 2001 Elsevier Science (USA).)

Age-related changes in attention and interval timing as a function of time of day were examined using a temporal bisection task with single and compound auditory and visual stimuli. Half of the participants in each age group were tested in the morning, and half were tested in the afternoon. Duration judgments were found to be shorter for visual signals than for auditory signals. This discrepancy was greater in the morning than in the afternoon and larger for the older than for the younger adults. Young adults showed equal sensitivity to signal duration for single and compound trials and higher sensitivity in the afternoon than in the morning for both signal modalities. In contrast, older adults showed impaired sensitivity on compound trials and the greatest sensitivity overall to single visual trials in the morning. These results suggest that age-related reductions in attentional resources may cause older adults to focus on signals that require controlled attention during specific phases of the circadian cycle.

Nicotine has been shown to improve attentiveness in smokers and attenuate attentional deficits in Alzheimer's disease patients, schizophrenics and adults with attention-deficit/hyperactivity disorder (ADHD). The current study was conducted to determine whether nicotine administered via transdermal patches would improve attentiveness in non-smoking adults without attentional deficits. The subjects underwent the nicotine and placebo exposure in a counterbalanced double-blind manner. Measures of treatment effect included the Profile of Mood States (POMS), Conners' computerized Continuous Performance Test (CPT) of attentiveness and a computerized interval-timing task. The subjects were administered a 7 mg/day nicotine transdermal patch for 4.5 h during a morning session. Nicotine significantly increased self-perceived vigor as measured by the POMS test. On the CPT, nicotine significantly decreased the number of errors of omission without causing increases in either errors of commission or correct hit reaction time. Nicotine also significantly decreased the variance of hit reaction time and the composite measure of attentiveness. This study shows that, in addition to reducing attentional impairment, nicotine administered via transdermal patches can improve attentiveness in normal adult non-smokers.

Our purpose was to infer the characteristics of the internal clock, temporal memory, and decision processes involved in temporal generalization behavior on the basis of the analysis of individual trials. Three groups of 10 rats each were trained on a peak procedure with reinforcement at 15, 30, or 60 s, with several nonfood trial durations. On nonfood trials, the mean response rate gradually increased to a maximum near the time that reinforcement sometimes occurred and then gradually decreased. Individual trials were characterized by a period of high response rate, preceded and followed by a low response rate. The covariance pattern among measures of the temporal characteristics of the high response rate (start, stop, middle, and spread) supported a parallel, scalar timing model in which animals used on each trial a single sample from memory of the time of reinforcement and separate response thresholds to decide when to start and stop responding. An alternative model, the quasi-serial model (J. Gibbon & R. M. Church, 1992), was not consistent with the obtained relationships between covariances or with the scalar property seen across different nonfood signal durations.

Postreinforcement signal processing by rats was demonstrated in six experiments that used a discrete-trials choice procedure. Experiment 1 assessed the extent to which rats are able to transfer knowledge about associations between postreinforcement signal durations and choice responses to conditions where a particular signal duration preceded the opportunity to make a choice response. In Experiment 2 the generality of the transfer effect was demonstrated by using both signal duration and signal modality as relevant stimulus attributes for the postreinforcement signals. The role of the relative durations of the reinforcement-signal gap and the intertrial interval was investigated in Experiment 3. In order to assess the effects of within-trial and between-trial signal relations on the acquisition of a temporal discrimination, both pre-and postreinforcement signals were presented on each trial in Experiments 4 and 5. The effects of pre- and postreinforcement signal relations on the steady-state performance of a temporal bisection task across three different signal ranges were studied in Experiment 6. The conclusion is that rats readily process various stimulus attributes of postreinforcement signals and that relations between postreinforcement signals, choice responses, and prereinforcement signals are major determinants of choice behavior.

The brain mechanisms involved in attention and memory were examined by testing rats in temporal discriminations designed to emphasize these cognitive processes. Normal rats were able to time each of two stimuli whether they were presented alone or together. Rats with lesions of the frontal cortex (FC) or nucleus basalis magnocellularis (NBM) were able to time each stimulus when it was presented alone, but not when it was presented together with another stimulus. Rather, these rats timed only the intruding stimulus and ignored the other, demonstrating a failure of divided attention. Rats with lesions of the fimbria-fornix (FF) or medial septal area (MSA) performed the divided attention task normally, but failed to remember the duration of a stimulus that had been terminated temporarily earlier in the trial, demonstrating a failure of working memory. These results provide another informative dissociation between the functions of the frontal and hippocampal systems, emphasizing frontal involvement in attention, and hippocampal involvement in working memory.

Both the presentation of unbalanced stimulus probabilities and the insertion of a predictive cue prior to the signal on each trial apparently induces a strong bias to use a particular stimulus modality in order to select a temporal criterion and response rule. This attentional bias toward one modality is apparently independent of the modality of the stimulus being timed and is strongly influenced by stimulus probabilities or prior warning cues. These techniques may be useful to control trial-by-trial sequential effects that influence a subject's perceptual and response biases when signals from more than one modality are used in duration discrimination tasks. Cross-procedural generality of the effects of attentional bias was observed. An asymmetrical modality effect on the latency to begin timing was observed with both the temporal bisection and the peak procedure. The latency to begin timing light signals, but not the latency to begin timing sound signals, was increased when the signal modality was unexpected. This asymmetrical effect was explained with the assumption that sound signals close the mode switch automatically, but that light signals close the mode switch only if attention is directed to the light. The time required to switch attention is reflected in a reduction of the number of pulses from the pacemaker that enter the accumulator. One positive aspect of this work is the demonstration that procedures similar to those used to study human cognition can be used with animal subjects with similar results. Perhaps these similarities will stimulate animal research on the physiological basis of various cognitive capacities. Animal subjects would be preferred for such physiological experimentation if it were established that they possessed some of the cognitive processes described by investigators of human information processing. One of the negative aspects of this work is that only one combination of modalities was used and variables such as stimulus intensity, stimulus probability, and range of signal durations have not been adequately investigated at present. Future work might test additional combinations of modalities and vary stimulus intensity and stimulus probability within a signal detection theory (SDT) framework to determine the effects of these variables on attentional bias.