Scalar expectancy theory and peak-interval timing in humans.

The properties of the internal clock, temporal memory, and decision processes used to time short durations were investigated. The peak-interval procedure was used to evaluate the timing of 8-, 12-, and 21-s intervals, and analyses were conducted on the mean response functions and on individual trials. A distractor task prevented counting, and visual feedback on accuracy and precision was provided after each trial. Mean response distributions were (a) centered at the appropriate real-time criteria, (b) highly symmetrical, and (c) scalar in their variability. Analysis of individual trials indicated more memory variability relative to response threshold variability. Taken together, these results demonstrate that humans show the same qualitative timing properties that other animals do, but with some quantitative differences. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Simultaneous timing of multiple intervals: Implications of the scalar property.

Three experiments with pigeons are reported in which the scalar property in simultaneous timing tasks was studied. According to scalar expectancy theory, the scalar property should be maintained in simultaneous timing, but the behavioral theory of timing predicts that the scalar property should be evident only in independent timing. Experiment 1 showed that the appearance of distinct peaks at reinforcement times required about a 4:1 ratio between intervals. Experiment 2 (2-interval timing task) and Experiment 3 (3-interval timing task) used an individual trial analysis technique to examine high-rate responding segments bracketing the times of reinforcement. The standard deviations of the starting and stopping times of high-rate segments were linearly related to their means and to reinforcement time, supporting the scalar property in simultaneous timing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Systematic nonlinearities in the perception of temporal intervals

Rats judged time intervals in a choice procedure in which accuracy was maintained at approximately 75% correct. Sensitivity to time (d') was approximately constant for short durations 2.0-32.0 s with 1.0- or 2.0-s spacing between intervals (n = 5 in each group, Experiment 1), 2.0-50.0 s with 2.0-s spacing (n = 2, Experiment 1), and 0.1-2.0 s with 0.1- or 0.2-s spacing (n = 6 in each group, Experiment 2). However, systematic departures from average sensitivity were observed, with local maxima in sensitivity at approximately 0.3, 1.2, 10.0, 24.0, and 36.0 s. Such systematic departures from an approximately constant d' are predicted by a connectionist theory of time with multiple oscillators and may require a modification of the linear timing hypothesis of scalar timing theory.     

Scalar timing in temporal generalization in humans with longer stimulus durations

Three experiments investigated temporal generalization performance in humans by using stimulus durations similar to those previously used with rats. In most conditions, chronometric counting was prevented by concurrent shadowing of temporally irregular numbers. Experiment 1 examined performance with visual stimuli, when the standard was 4.0 s long and nonstandard stimuli were spaced either linearly or logarithmically around the standard. Generalization gradients were asymmetrical with linear spacing but symmetrical with logarithmic spacing, a result obtained previously with humans. Experiment 2 used auditory stimuli and varied the standard across values of 2.0, 4.0, 6.0, and 8.0 s. All gradients were asymmetrical, and good superposition was obtained, indicating conformity to scalar timing. Experiment 3 prevented or encouraged chronometric counting by changing instructions, and temporal generalization gradients differed when counting was and was not used.     

When to start explicit counting in a time-intervals discrimination task: A critical point in the timing process of humans.

Four interval discrimination experiments were conducted to determine the interval length at which explicit counting becomes a useful strategy. Experiment 1 showed that for intervals lasting about 1 s, there was no advantage to counting regardless of the counting strategy adopted. Experiment 2 showed that for 2.5-s intervals, performance was much better with an explicit-counting strategy. To study the functional relationship between variability and duration in the counting versus no-counting conditions, variability was estimated for base durations lasting 0.7–1.9 s in Experiment 3. This experiment showed that the generalized form of Weber's law applied well to data in the no-counting condition. Experiment 4 showed that variability remained the same for durations lasting 1.3–1.9 s when an explicit-counting strategy was adopted. Taken together, the experiments showed that it becomes useful to count explicitly when intervals are longer than 1.18 s. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perception and production of brief durations: Beat-based versus interval-based timing.

Two experiments examined whether timing of short intervals is beat- or interval-based. In Experiment 1, subjects heard a sequence of standard tones followed by 2 test tones; they compared the interval between test tones to the interval between the standards. If optimal precision required beat-based timing, performance should be best in blocks in which the interval between standard and test reliably matched the standard interval. No such effect was observed. In Experiment 2, subjects heard 2 test tones and reproduced the intertone interval by producing 2 keypress responses. Entrainment to the beat was apparent: First-response latency clustered around the standard interval and was positively correlated with the produced interval. However, responses occurring on or near the beat showed no better temporal fidelity than off-beat responses. One plausible interpretation of these findings is that the brain always times brief intervals with an interval timer; however, this timer can be used in a cyclic fashion to trigger rhythmic responses. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sex differences, context preexposure, and the immediate shock deficit in Pavlovian context conditioning with mice.

The acquisition of context fear in rats is affected by variables such as the sex of the animal, the placement to shock interval (PSI), and preexposure to the context. The current experiments assessed the effects of these variables on context conditioning in mice (C57BL/6). In Experiment 1, mice were placed in a chamber and received a single shock 5 s, 20 s, 40 s, 60 s, 180 s, or 720 s later. Increasing the PSI produced corresponding increases in conditional freezing during the context test. In addition, male mice acquired more context conditioning than female mice did but only at intermediate PSIs. In Experiment 2, preexposure to the context before training alleviated the sex difference found with an intermediate PSI. The results are discussed in terms of configural learning theory and are argued to be contrary to the predictions of scalar expectancy theory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Circadian time perception.

The variability of anticipating a meal was investigated. Sprague-Dawley rats earned food by inspecting a food source during a 3-hr interval. Food was not available at other times. In Experiment 1, the meal started 3 or 7 hr after light offset in a 12-hr light-dark cycle. Experiment 2 was conducted in constant darkness with 14-, 22-, 22.5-, 24-, 25.5-, 26-, or 34-hr intermeal intervals. Inspections increased before the meal. Rats timed intervals in the circadian range (22–26 hr) with lower variability than that for intervals outside this range (3–14 and 34 hr). Higher precision in timing selected intervals violates the scalar property. Proximity to a circadian oscillator improves timing precision. Variability may be used to identify oscillators with noncircadian periods. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Impaired timing precision produced by striatal D2 receptor overexpression is mediated by cognitive and motivational deficits.

Increased striatal dopamine D2 receptor activity is thought to contribute to the pathophysiology of schizophrenia. To model this condition in mice, Kellendonk et al. (2006) generated transgenic mice that selectively overexpress the D2 receptor in striatum (D2OE). Drew et al. (2007) reported that D2OE mice display deficits in interval timing and motivation. The present study further explored the impaired timing in D2OE mice. Experiment 1 assessed the role of motivation in producing timing deficits in the peak procedure and found that performance in D2OE mice was improved by increasing motivation. In addition, performance was impaired in control mice when motivation was decreased. In Experiment 2, we found that D2OE mice have no timing impairment when tested using the bisection task, a procedure in which the measure of timing performance is less influenced by motivation to respond. In Experiment 3, we also used the bisection task and found selective impairment in timing of long durations in D2OE mice. These results suggest that striatal D2 overexpression impairs timing by decreasing motivation and through its impact on working memory and/or sustained attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perception and production of temporal intervals across a range of durations: Evidence for a common timing mechanism.

Study participants performed time perception and production tasks over a set of 4 intervals ranging from 325 to 550 ms. In 3 experiments, variability on both the production and perception tasks was found to be linearly related to the square of the target intervals. If the perception and production of short temporal intervals use a common timing mechanism, the slopes of the functions for the 2 tasks should be identical. The results of Experiment 1 failed to support this prediction. However, when the 2 tasks were made more similar by providing a single (Experiment 2) or multiple (Experiment 3) presentations of the target interval per judgment or production, the perception and production functions were nearly identical. The results suggest that temporal judgments and productions are based on an integrated internal representation of the target interval rather than reference to an internal oscillatory process. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Strain distribution of mice in discriminated Y-maze avoidance learning: Genetic and procedural differences.

The current study was conducted to characterize discriminated avoidance learning in mice by using a Y-maze task. In Experiment 1, the task parameters were manipulated, including the amount of time spent in the start arm, the amount of time to make the avoidance response, and the intertrial interval (ITI) using C57?×?SJL F1 hybrid mice. Avoidance performance was significantly improved with longer times to avoid the shock and longer ITIs. In Experiment 2, mice from 4 inbred strains (BALB/cByJ, DBA/2J, C57BL/6J, and SJL/J), an F1 hybrid (C57?×?SJL), and 1 outbred strain (CD1) were tested with various ITIs. Strain differences were observed in avoidance learning, with BALB, DBA, C57?×?SJL and CD1 mice showing significantly better avoidance learning than C57 mice, which were better than SJL mice. These data demonstrate that Y-maze performance is significantly influenced by the genetic background of the mouse and the parameters of the task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Precision and accuracy in the reproduction of simple tone sequences.

In four experiments we investigated the precision and accuracy with which amateur musicians are able to reproduce sequences of tones varied only temporally, so as to have tone and rest durations constant over sequences, and the tempo varied over the musically meaningful range of 5–0.5 tones per second. Experiments 1 and 2 supported the hypothesis of attentional bias toward having the attack moments, rather than the departure moments, precisely timed. Experiment 3 corroborated the hypothesis that inaccurate timing of short interattack intervals is manifested in a lengthening of rests, rather than tones, as a result of larger motor activity during the reproduction of rests. Experiment 4 gave some support to the hypothesis that the shortening of long interattack intervals is due to mnemonic constraints affecting the rests rather than the tones. Both theoretical and practical consequences of the various findings, particularly with respect to timing in musical performance, are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Estradiol modulation of the speed of an internal clock.

Estradiol significantly influences dopamine (DA) activity in the striatum (e.g., J. B. Becker, 1990b), and researchers have strongly implicated striatal DA in the regulation of temporal integration in the seconds-to-minutes range (e.g., W. H. Meck, 1996). In the current experiment, the author examines the effect of acute estradiol administered prior to testing on a peak-interval (PI) timing task. The administration of 5 μg of estradiol 30 min prior to testing resulted in an immediate and proportional leftward shift in the timing functions relative to the PI functions obtained following the administration of the oil vehicle. The precision of the response functions was increased in a manner commensurate with the scalar property of interval timing without significant alteration of peak response rates. When timing behavior was assessed 3 days following estradiol or oil administration, no differences were found in the peak time of responding or in the precision of responding between estradiol- and oil-treated rats, indicating that the effects of estradiol on these measures of interval timing are short lived. Together, these findings indicate that estradiol selectively increases the speed of an internal clock, perhaps through facilitating striatal DA activity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Peak procedure performance in young adult and aged rats: acquisition and adaptation to a changing temporal criterion

Twenty-four-month-old and 4-month-old rats were trained on a peak-interval procedure, where the time of reinforcement was varied twice between 20 and 40 sec. Peak times from the old rats were consistently longer than the reinforcement time, whereas those from younger animals tracked the 20- and 40-sec durations more closely. Different measures of performance suggested that the old rats were either (1) systematically misremembering the time of reinforcement or (2) using an internal clock with a substantially greater latency to start and stop timing than the younger animals. Old rats also adjusted more slowly to the first transition from 20 to 40 sec than did the younger ones, but not to later transitions. Correlations between measures derived from within-trial patterns of responding conformed in general to detailed predictions derived from scalar expectancy theory. However, some correlation values more closely resembled those derived from a study of peak-interval performance in humans and a theoretical model developed by Cheng and Westwood (1993), than those obtained in previous work with animals, for reasons that are at present unclear.     

Timing and classifying brief acoustic stimuli by songbirds and humans.

The durations of animals' brief vocalizations provide conspecifics with important recognition cues. In the present experiments, zebra finches and humans (trained musicians) were rewarded for responding after S+ (standard) auditory signals from 56 to 663 ms; and not for responding, after shorter or longer S– (comparison) durations from 10 to 3684 ms. With either a single standard (Experiment 1) or multiple standards (Experiment 2), both zebra finches and humans timed brief signals to about the same level of accuracy. The results were in qualitative agreement with predictions from scalar timing theory and its connectionist implementation in both experiments. The connectionist model provides a good quantitative account of temporal gradients with a single standard (Experiment 1) but not with multiple standards (Experiment 2). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The perching response and the laws of animal timing.

Homing pigeons were trained under differential-reinforcement-of-low-rate (DRL) or differential-reinforcement-of-response-duration (DRRD) schedules using a perching response. Schedule values ranged from 10 s to 70 s for DRL and from 12 s to 40 s for DRRD. In general, mean interresponse times or response durations were very close to the schedule requirement at all schedule values. A linear relation between mean response measure and schedule value described the data well, but power functions fared even better. The data also conformed well to the generalized Weber law; standard deviations of response measures varied as a linear function of the mean. Overall, the perching response produced data that conformed much more accurately to the schedule requirement—particularly at the longer schedule values—than did data from previous studies with both rats and pigeons. The results conformed well to the linear-type timing consistent with scalar timing theory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Traumatic brain injury causes delayed motor and cognitive impairment in a mutant mouse strain known to exhibit delayed Wallerian degeneration

Delayed Wallerian degeneration after neuronal injury is a feature of the C57BL/Wld(s) mouse mutant. In the present study, we examined the effect of unilateral controlled cortical impact (CCI) on motor and cognitive performance in C57BL/6 and C57BL/Wld(s) mice. Performance on a beam-walking task was impaired in both injured groups over the first 3 weeks; however, between 28 and 35 days post injury, C57BL/6 mice continued to improve whereas C57BL/Wld(s) mice showed increased footfaults. In a spatial learning task, C57BL/Wld(s) animals performed consistently better than C57BL/6 mice when tested 7-10 days and 14-17 days following CCI. C57BL/Wld(s) mice also demonstrated improved working memory performance as compared with C57BL/6 mice when trained on days 21-22 after injury; this effect was lost on days 23 and 24, and was not evident in other animals tested in the same task at 28-31 days following injury. These results indicate a marked delay in motor and cognitive impairment following CCI in C57BL/Wld(s) mice compared with injured C57BL/6 controls. This is consistent with previous work showing delayed temporal evolution of neuronal degeneration in C57BL/Wld(s) mice and suggests CCI may be a suitable model for examining the functional consequences of traumatic brain injury (TBI) in genetically altered mice.     

Ontogeny of eyeblink conditioned response timing in rats.

Eyeblink conditioned response (CR) timing was assessed in adult and infant rats. In Experiment 1, adult rats were trained with a 150-ms tone conditioned stimulus (CS) paired with a periorbital shock unconditioned stimulus (US; presented at 200- or 500-ms interstimulus intervals [ISIs]). The rats acquired CRs with 2 distinct peaks that occurred just before the US onset times. Experiments 2 and 3 examined developmental changes in CR timing in pups trained on Postnatal Days 24-26 or 32-34. Experiment 3 used a delay conditioning procedure in which the tone CS continued throughout the ISIs. Pups of both ages exhibited robust conditioning. However, there were age-related increases in the percentage of double-peaked CRs and in CR timing precision. Ontogenetic changes in eyeblink CR timing may be related to developmental changes in cerebellar cortical or hippocampal function. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Latent timing in human conditioned avoidance.

Four experiments explored signal timing in human conditioned avoidance. Participants received discrimination training with different duration signals that announced the outcome (S+) or not (S-). Temporal discrimination and superposition of performance to S+ signals of different length (3, 6, or 9 s) was found both in within-subjects (Experiment 1a) and between-subjects (Experiment 1b) designs. S- signals also produced a temporal discrimination and superposition effect during a single test trial conducted after the meaning of the signals was reversed through instructions. Experiments 2a and 2b replicated these results in a situation in which (a) the durations of the S+ and S- signals were different (4.5 or 9 s) to prevent any temporal generalization between them (Experiment 2a), and (b) only S- signals were presented during training, precluding developing of inhibition to S- (Experiment 2b). These results show that participants time both S+ and S- signals in human conditioned avoidance, and they further suggest that the timing of a cue is independent of reinforcement. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modeling the effects of the NMDA receptor antagonist MK-801 on timing in rats.

The NMDA receptor antagonist MK-801 produces different effects on timing tasks. In particular, MK-801 produces an underestimation of duration when animals are tested with the differential reinforcement of low rate of responding (DRL) schedule and an overestimation of duration when animals are tested with the peak-interval (PI) procedure. The goal of this study was to develop a model-based explanation for this discrepancy. Two computer simulations were conducted via an implementation of scalar expectancy theory (SET). In Simulation 1, SET was used to provide a quantitative account of PI timing data. Simulation 2 used parameter estimates from Simulation 1 to predict effects of MK-801 on the DRL task. DRL predictions provided a close match to previous empirical data. Results of the simulations suggest that differences in the literature are likely due to inherent differences between PI and DRL tasks, rather than fundamental differences in timing. Overall, the role of NMDA receptors in timing appears to be multifaceted, impacting perception, memory, and decision processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)