J. H. Wearden

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 duration 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 datasuggested 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.

Scalar properties in human timing: Conformity and violations

The article reviews data from animal subjects on a range of timing tasks (including fixed-interval and temporal differentiation schedules, stimulus timing, aversive conditioning, and Pavlovian methods) with respect to conformity to the two scalar properties of timing behaviour: mean accuracy and scalar (Weberian) variance. Systematic deviations were found in data from temporal differentiation schedules, timing of very short (<100 ms) or very long (>100 s) durations, effects of “task difficulty”, and some special cases where circadian and interval timing seemed to interact, or where some specific durations seemed to be timed more precisely than others. Theoretical reconciliation of some of these deviations with underlying scalar timing can be achieved, but a number of problematical cases remain unexplained.

Stimulus spacing 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.

Do humans possess an internal clock with scalar timing properties

Abstract The question of whether humans possess an internal clock with scalar timing properties was discussed with reference to three sorts of experiments. First, evidence from experiments on interval production was presented which showed that interval production by humans that is not based on chronometric counting exhibited approximate scalar properties as (i) mean times produced increased linearly with real time, and (ii) coefficients of variation of times produced varied unsystematically (in the range 0.10 to 0.16) as the time produced varied. Second, an experiment measuring the intercount units used by subjects in chronometric counting revealed that count units exhibited approximate scalar properties, with their coefficient of variation remaining roughly constant (in the range 0.10 to 0.14) as intercount interval changed. A simple model of chronometric counting based on scalar properties of count units was shown to be compatible with the declining coefficients of variation with increases in interval produced found in the overall time judgments based on chronometric counting. Finally, two experiments with normal humans which were analogs of animal experiments on interval bisection and temporal generalization were discussed. Here, human performance differed from that found in animals in both cases, suggesting that the way humans make judgments about intervals differs systematically from the judgmental processes of animals, but models of behavior consistent with underlying scalar representations of duration could be developed. Overall, all three sorts of experiments produced evidence suggesting that human timing can, in some circumstances, be described well by a scalar timing mechanism.

Speeding up an Internal Clock in Children? Effects of Visual Flicker on Subjective Duration:

Children of 3, 5, and 8 years of age were trained on a temporal bisection task where visual stimuli in the form of blue circles of 200 and 800 ms or 400 and 1600 ms duration, preceded by a 5-s white circle, served as the short and long standards. Following discrimination training between the standards, stimuli in the ranges 200-800 ms or 400-1600 ms were presented with the white circle either constant or flickering. Relative to the constant white circle, the flicker (1) increased the proportion of “long” responses (responses appropriate to the long standard), (2) shifted the psychophysical functions to the left, (3) decreased bisection point values, at all ages, and (4) did not systematically affect measures of temporal sensitivity, such as difference limen and Weber ratio. The results were consistent with the idea that the repetitive flicker had increased the speed of the pacemaker of an internal clock in children as young as 3 years. The “pacemaker speed” interpretation of the results was further strengthened by a greater effect of flicker in the 400/1600-ms condition than in the 200/800-ms condition.

Feeling the Heat: Body Temperature and the Rate of Subjective Time, Revisited

Experiments investigating timing behaviour in humans under conditions where body temperature was raised or (much more rarely) lowered, dating from 1927 to 1993, were reviewed. These tested the hypothesis that humans possess a temperature-sensitive chemical or biological internal clock. Most studies used conditions in which subjects produced or estimated durations less than 100 sec long, probably using chronometric counting, but other experimental paradigms were sometimes employed. Data from each study were expressed in a uniform fashion, as plots of changes in the rate of subjective time (estimated from changes in timing behaviour) against changes in body temperature. In almost all cases, rate of subjective time increased when body temperature increased above normal, and decreased when body temperature was lowered below normal, although observations of the latter type were rare. The data also suggested a parametric effect of body temperature, with higher temperatures generally producing faster subjective time. Some possible mechanisms for the effects obtained were discussed, with the most promising explanation probably being that the temperature manipulation produces changes in arousal.

''Beyond the fields we know...'': exploring and developing scalar timing theory

The article discusses three areas that appear neglected or underdeveloped in current treatments of scalar timing theory (SET). In particular, questions about where variance in the SET system comes from, and how memory and decision processes operate within SET are discussed. The article suggests a number of possible experiments with humans, some based on pilot work which is described, that may clarify all three areas to some degree. Methods derived from conventional studies of memory are suggested as providing techniques for investigating the operation of memory and decision processes within the SET model, both areas previously considered somewhat inaccessible. In general, the tripartite division of SET into clock, memory, and decision processes is advocated as a useful general framework for studying timing, including questions related to its neurobiological basis, whether or not data always conform to SET predictions, although more needs to be known about how all three parts of the SET system operate.

Across the Great Divide Animal Psychology and Time in Humans

A substantial proportion of current research on the experimental psychology of time is conducted with animals, and a large body of data and theory derived from animal studies has been collected. Commentators disagree about how useful such data and theories are for understanding human timing. The paper discusses advantages and limitations of animal studies. The limitations are (i) some human timing phenomena are outside the scope of investigations with animals, for both psychological and methodological reasons, and (ii) even when data from humans and animals are similar there is no guarantee of similarity of psychological processes. Nevertheless, some striking examples of the fruitfulness of animal/human timing comparisons have been found in areas of interval production, judgements of stimulus duration, and memory for duration.

Vierordt's The Experimental Study of the Time Sense (1868) and its legacy

The paper discusses the results from Vierordts 1868 book Der Zeitsinn nach Versuchen [The Experimental Study of the Time Sense]. Illustrations of “Vierordts Law”, the proposition that short durations are judged as longer than they really are, whereas long durations are judged as shorter, with an “indifference point” in between, are provided, mainly from reproduction experiments where Vierordt and his students or colleagues served as experimental participants. Other work from Der Zeitsinn including time discrimination and categorical timing procedures is also presented. Some subsequent research on Vierordts Law and the “indifference point” is discussed with respect to some issues in contemporary timing theory.

Age and IQ effects on stimulus and response timing

Normal older participants (aged 60-79 years), with known scores on the Culture Fair Intelligence Test, were tested on 4 timing tasks (i.e., temporal generalization, bisection, differential threshold, and interval production). The data were related to the theoretical framework of scalar timing theory and ideas about information processing and aging. In general, increasing age and decreasing IQ tended to be associated with increasing variability of judgments of duration, although in all groups events could be timed on average accurately. In some cases (e.g., bisection), performance differences between the older participants and students nearly 50 years younger used in other studies were negligible.