Biomedical subjects

J H Wearden

Publications and source records attributed to J H Wearden.

At least 19 recordsLinked to original sources

PubMed2006

About Skinner and time: behavior-analytic contributions to research on animal timing.

The article discusses two important influences of B. F. Skinner, and later workers in the behavior-analytic tradition, on the study of animal timing. The first influence is methodological, and is traced from the invention of schedules imposing temporal constraints or periodicities on animals in The Behavior of Organisms, through the rate differentiation procedures of Schedules of Reinforcement, to modern temporal psychophysics in animals. The second influence has been the development of accounts of animal timing that have tried to avoid reference to internal processes of a cognitive sort, in particular internal clock mechanisms. Skinner's early discussion of temporal control is first reviewed, and then three recent theories-Killeen & Fetterman's (1988) Behavioral Theory of Timing; Machado's (1997) Learning to Time; and Dragoi, Staddon, Palmer, & Buhusi's (2003) Adaptive Timer Model-are discussed and evaluated.

Animals↗

PubMed2005

"The stone which the builders rejected...": Delay of reinforcement and response rate on fixed-interval and related schedules.

The article deals with response rates (mainly running and peak or terminal rates) on simple and on some mixed-FI schedules and explores the idea that these rates are determined by the average delay of reinforcement for responses occurring during the response periods that the schedules generate. The effects of reinforcement delay are assumed to be mediated by a hyperbolic delay of reinforcement gradient. The account predicts that (a) running rates on simple FI schedules should increase with increasing rate of reinforcement, in a manner close to that required by Herrnstein's equation, (b) improving temporal control during acquisition should be associated with increasing running rates, (c) two-valued mixed-FI schedules with equiprobable components should produce complex results, with peak rates sometimes being higher on the longer component schedule, and (d) that effects of reinforcement probability on mixed-FI should affect the response rate at the time of the shorter component only. All these predictions were confirmed by data, although effects in some experiments remain outside the scope of the model. In general, delay of reinforcement as a determinant of response rate on FI and related schedules (rather than temporal control on such schedules) seems a useful starting point for a more thorough analysis of some neglected questions about performance on FI and related schedules.

Animals↗

PubMed2005

Episodic temporal generalization: a developmental study.

Groups of 5-year-olds, 10-year-olds, and adults completed either an episodic temporal generalization task, in which no stimuli were repeated, or a repeated standard temporal generalization task, in which there was a fixed standard that was repeated on every trial. Significant developmental improvements were found on both tasks. In both tasks, gradients of performance over two different stimulus ranges superimposed well when plotted on the same relative scale. Performance was similar for the adults and 10-year-olds across tasks, but the 5-year-olds performed better on the repeated standard task. These findings suggest that perceptual processes are a source of scalar variability in timing, and that there are developmental changes in levels of such variability.

Adult↗

PubMed2004

Reinforcer concentration effects on a fixed-interval schedule.

Four rats received training on a mixed FI 30-s FI 150-s schedule, where the different FI values were associated with different levers. During baseline, the reinforcer was a 30% concentration of condensed milk. During subsequent testing sessions, the reinforcer concentration was varied within sessions over values of 10, 30, 50, and 70%. Measures of behaviour were taken from the FI 30-s lever during trials where the reinforcer was delivered for responses on the other lever. Increasing the reinforcer concentration which began the interval (a) increased the time to start responding in the interval, and (b) increased the location of the response peak on the FI 30-s lever (often to values well above 30s). Response rate at the peak, and spread of the response rate versus time function, changed much less with reinforcer concentration. The data are discussed relative to predictions derived from Scalar Expectancy Theory, the Behavioural Theory of Timing, and the Tuned-trace model.

Animals↗

PubMed2004

Double standards: memory loading in temporal reference memory.

Three experiments compared human performance on temporal generalization tasks with either one or two different, and distinct, standard durations encoded. In the first two experiments participants received presentations of two different standards at the beginning of each trial block and were instructed to encode either one or both of them. When instructed to encode one standard they then had to judge whether each of a number of comparison stimuli was or was not that standard. When instructed to encode both they were then tested using just one of the standards but the participants were unaware, at the time of encoding, which standard would later be used as a reference. No marked effect of the number of temporal standards encoded was found. In Experiment 3 participants received either one or two temporal standards and had to use both when two were presented. This manipulation produced flatter generalization gradients when two standards were encoded than when just one was, and modelling attributed this difference mainly to an increase in reference memory variability in the double-standard case. This suggests that the variability of representation of durations in temporal reference memory can be systematically increased by increasing temporal reference memory load.

Adolescent↗

PubMed2003

Multiple-interval timing in rats: Performance on two-valued mixed fixed-interval schedules.

Three experiments studied timing in rats on 2-valued mixed-fixed-interval schedules, with equally probable components, Fixed-Interval S and Fixed-Interval L (FI S and FI L, respectively). When the L:S ratio was greater than 4, 2 distinct response peaks appeared close to FI S and FI L, and data could be well fitted by the sum of 2 Gaussian curves. When the L:S ratio was less than 4, only 1 response peak was usually visible, but nonlinear regression often identified separate sources of behavioral control, by FI S and FI L, although control by FI L dominated. Data were used to test ideas derived from scalar expectancy theory, the behavioral theory of timing, and learning to time.

Animals↗

PubMed2003

More is not necessarily better: Examining the nature of the temporal reference memory component in timing.

Three experiments compared the timing performance of humans on a modified temporal generalization task with 1, 3, or 5 presentations of the standard duration. In all three experiments subjects received presentations of a standard duration at the beginning of a trial block and then had to judge whether each of a number of comparison stimuli was or was not the standard. The duration of the standard changed between blocks. The three experiments varied the experimental design (between or within subjects), task difficulty (how closely the comparison stimuli were spaced around the standards), and presence or absence of feedback on performance accuracy. Number of presentations of the standard never affected the proportion of identifications of the standard when it was presented, nor other features of the temporal generalization gradients observed. The implications for the operation of reference memories within the scalar timing system were explored via models that made different assumptions about how the individual presentations of the standard were stored and used.

Generalization, Psychological↗

PubMed2002

Is subjective shortening in human memory unique to time representations?

Three experiments compared forgetting of the duration of a bar-like visual stimulus with forgetting of its length. The main aim of the experiments was to investigate whether subjective shortening (a decrease in the subjective magnitude of a stimulus as its retention interval increased) was observable in length judgements as well as in time judgements, where subjective shortening has been often observed previously. On all trials of the three experiments, humans received two briefly presented coloured bars, separated by a delay ranging from 1 to 10 s, and the bars could differ in length, duration of presentation, or both. In Experiment 1 two groups of subjects made either length or duration judgements, and subjective shortening-type forgetting functions were observed only for duration. Experiments 2 and 3 used the same general procedure, but the stimuli judged could differ both in length and duration within a trial, and different subject groups (Experiment 2) or the same subjects in two conditions (Experiment 3) made either length or duration judgements of stimuli, which were on average physically identical. Subjective shortening was only found with duration, and never with length, supporting the view that subjective shortening may be unique to time judgements.

Adult↗

PubMed2002

Traveling in time: a time-left analogue for humans.

Two experiments studied normal humans in an analogue of the time-left procedure of J. Gibbon and R. M. Church (1981). In Experiment 1 the "standard" alternative (S) was always half the length of the "comparison" time-left link (C), and S ranged from 4 to 8 s. Humans showed an increasing preference for the time-left alternative with increasing elapsed time in the interval, and indifference points strongly supported the idea of a linear, rather than a logarithmic, time scale. Experiment 2 used some conditions in which S was greater or less than C/2, and preference for the time-left alternative varied systematically with the S/C ratio. Data from both experiments showed reasonable superposition, suggesting underlying scalar timing processes in time left in humans.

Choice Behavior↗

PubMed2001

Temporal bisection in children.

Children aged 3, 5, and 8 years received training on a temporal bisection task, with standard short and long durations being presented as visual stimuli lasting 1 and 4 s or 2 and 8 s. Nonstandard comparison stimuli were spaced linearly between the standards. Psychophysical functions showed increasing proportions of "long" responses (responses appropriate to the long standard) with increasing stimulus duration, but were flatter in the younger children than in the 8-year-olds. Bisection points (the stimulus duration giving rise to 50% "long" responses) were close to the arithmetic mean of the short and long standards in most conditions. Statistical analyses and results from different theoretical models of the data all suggested that temporal sensitivity was higher in the 8-year-olds than in the younger groups, even when the possibility of random responding was controlled for.

Age Factors↗

PubMed2001

Scalar timing without reference memory? Episodic temporal generalization and bisection in humans.

Three experiments tested whether the scalar property of timing could occur when humans timed short durations under conditions in which it was unlikely that they developed reference memories of temporal "standards". Experiment 1 used an episodic version of a temporal generalization task where judgements were made of the potential equality of two durations presented on each trial. Unknown to the subject, one of these was always 200, 400, 600, or 800 ms, and the other was of variable duration. Temporal generalization gradients showed the scalar property of superimposition at standard values greater than 200 ms. Experiment 2 used a variant of the "roving bisection" method invented by Rodriguez-Girones and Kacelnik (1998) modified so that the scalar property of timing could be observed empirically. Data from bisection with short/long standard pairs of 100/400, 200/800, and 300/1,200 ms showed nearly perfect scalar-type superimposition. Experiment 3 again used episodic temporal generalization, but durations were never repeated and came from three distinct time ranges. Superimposition was found across these ranges except for the shortest visual stimuli timed. The data suggested that scalar timing could occur in humans in conditions where the formation of reference memories of temporal standards was highly improbable.

Generalization, Psychological↗

PubMed1998

Why "sounds are judged longer than lights": application of a model of the internal clock in humans.

Three experiments, using temporal generalization and verbal estimation methods, studied judgements of durations of auditory (500-Hz tone) and visual (14-cm blue square) stimuli. With both methods, auditory stimuli were judged longer, and less variable, than visual ones. The verbal estimation experiments used stimuli from 77 to 1183 msec in length, and the slope of the function relating mean estimate to real length differed between modalities (but the intercept did not), consistent with the idea that a pacemaker generating duration representations ran faster for auditory than for visual stimuli. The different variability of auditory and visual stimuli was attributed to differential variability in the operation of a switch of a pacemaker-accumulator clock, and experimental data suggested that such switch effects were separable from changes in pacemaker speed. Overall, the work showed how a clock model consistent with scalar timing theory, the leading account of animal timing, can address an issue derived from the classical literature on human time perception.

Attention↗

PubMed1998

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.

Adaptation, Psychological↗

PubMed1997

Adjusting to changes in the time of reinforcement: peak-interval transitions in rats.

Thirty rats received training on a peak-interval procedure, where a baseline with a 20-s time of reinforcement was interspersed among cyclic transitions to other reinforcement time values (10, 20, 30, or 40 s), each of which was either in force for only a single session or for 3 sessions. Peak times were close to the time of reinforcement on the 20-s baseline and tracked the new reinforcement times both closely (but not exactly) and very rapidly. Peak time during transitions was affected by the criterion value in force on the previous session, exhibiting a proactive interference effect. Analysis of individual peak times during a session showed that transitions from lower to higher reinforcement time values were usually characterized by abrupt jumps in peak time, whereas descending transitions were mostly smooth but rapid.

Animals↗

PubMed1997

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.

Animals↗

PubMed1997

Temporal bisection in humans with longer stimulus durations.

Normal adults were tested in eight temporal bisection conditions, using 500-Hz tones as stimuli. Stimulus lengths matched, or overlapped with, durations normally used in bisection experiments with animals, and chronometric counting was prevented by using a concurrent digit-shadowing task. Four experimental groups were used to investigate any effects of stimulus spacing, and stimuli were logarithmically or linearly spaced between standard "short" and "long" durations of 1 and 4, or 2 and 8 sec. A slight leftward shift of the psychophysical function was found in the logarithmic spacing condition, relative to linear spacing. Four other groups tested the conjecture that the ratio of the short and long standards might play some role in determining the location of the bisection point, and conditions with long/short ratios of 2:1 and 5:1 were used. In all cases the bisection point was close to the arithmetic mean of the short and long standards, rather than the geometric mean, as in animal studies. Overall, however, smaller long/short ratios (which may indicate more difficult temporal discriminations) produced more sensitive timing. When the long/short ratio was held constant, however, data showed nearly perfect superimposition, indicating conformity to scalar timing. In general, results were similar to those from experiments with humans that used much shorter durations, indicating the animal/human differences in bisection do not depend on the absolute lengths of the stimuli used.

Humans↗

PubMed1996

Speeding up an internal clock in humans? Effects of click trains on subjective duration.

Four experiments investigated the effect of trains of clicks (usually 5 s long and at 5 or 25 Hz) on subjective duration in humans, as previous research had suggested that such a manipulation would speed up the pacemaker of an internal clock by increasing participants' arousal. The four experiments used temporal generalization, pair comparison of duration, verbal estimation, and production of short durations. In all cases, preceding the durations to be judged by clicks changed their subjective length in a manner broadly consistent with the idea that pacemaker speed was increased, by an average of about 10%.

Acoustic Stimulation↗

PubMed1996

Stimulus range effects in temporal bisection by humans.

Two experiments with human subjects, using short-duration tones as stimuli to be judged, investigated the effect of the range of the stimulus set on temporal bisection performance. In Experiment 1, six groups of subjects were tested on a temporal bisection task, where each stimulus had to be classified as "short" or "long". For three groups, the difference between the longest (L) and shortest (S) durations in the to-be-bisected stimulus set was kept constant at 400 msec, and the L/S ratio was varied over values of 5:1 and 2:1. For three other groups, the L/S ratio was kept constant at 4:1 but the L-S difference varied from 300 to 600 msec. The bisection point (the stimulus value resulting in 50% "long" responses) was located closer to the arithmetic mean of L and S than the geometric mean for all groups except that for which the L/S ratio was 2:1, in which case geometric mean bisection was found. In Experiment 2, stimuli were spaced between L and S either linearly or logarithmically, and the L/S ratio took values of either 2:1 or 19:1. Geometric mean bisection was found in both cases when the L/S ratio was 2:1, but effects of stimulus spacing were found only when the L/S ratio was 19:1. Overall, the results supported a previous conjecture that the L/S ratio used in a bisection task played a critical role in determining the behaviour obtained. A theoretical model of bisection advanced by Wearden (1991) dealt appropriately with bisection point shifts discussed above but encountered difficulties with stimulus spacing effects.

Adult↗