Helga Lejeune

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.

Brain Activation Induced by Estimation of Duration: A PET Study

Duration information about a visual stimulus requires processing as do other visual features such as size or intensity. Using positron emission tomography, iterative H215O infusions, and statistical parametric mapping, we investigated the neural correlates of time processing. Nine normal subjects underwent six serial rCBF. Three tasks were studied: (a) A temporal generalization task (D task) in which the subjects had to judge (by pressing one of two keys) whether the duration of the illumination of a green LED was equal to or different from that of a previously presented standard; (b) An intensity generalization task (I task) in which the judgment concerned the intensity of the LED; and (c) A control task (C task) in which the subjects had to press one of the two keys at random in response to LED illumination. A significant increase in rCBF during the D task, compared to that during the C task, was observed in right prefontal cortex, right inferior parietal lobule, anterior cingulate cortex, vermis, and a region corresponding to the left fusiform gyrus. A significant increase in rCBF during the I task, compared to that during the C task, was observed in right prefontal cortex, right inferior parietal lobule, right extrastriate cortex, anterior cingulate cortex, left inferior parietal lobule, vermis, and two symmetrical regions corresponding to the fusiform gyri. No significant activation was observed in the D task when compared to that in the I task. We propose that these cortical maps are best explained by the recruitment of visual attention and memory structures, which play a major role in prospective time judgements as indicated by behavioral studies. The data also suggest that the temporal dimension of a visual stimulus is processed in the same areas as other visual attributes.

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.

The comparative psychology of fixed-interval responding: Some quantitative analyses

Abstract Data on variation in the average relative frequency of responding with elapsed time since reinforcement during various fixed-interval schedules were available from cats, rats, woodmice, pigeons, turtle doves, a fish species Tilapia, and fresh-water turtles. These data were analyzed in a uniform manner by fitting Gaussian curves to the response frequency versus time functions, with the curve peak forced to be at the fixed-interval value. This analysis yielded a curve coefficient of variation (curve standard deviation/peak location), a measure of the precision of within-interval temporal control. Overall, Gaussian curves fitted data well, and two general trends could be noted. First, curve coefficient of variation tended to increase with increases in the fixed-interval value (although for most species used a range of interval values could be noted over which the coefficient of variation remained approximately constant). Second, different species differed markedly with respect to the absolute value of coefficient of variation obtained, by implication the quality of temporal control manifested. Lowest values (i.e., best temporal control) were obtained in data from cats, rats, and mice (as well as data from monkeys taken from another study). Pigeons produced higher values, then fish, then turtle doves (whose temporal control was markedly worse than that exhibited by pigeons), and finally turtles. A simple model deriving responding during fixed intervals from a mixture of timing and nontiming processes predicted that curve coefficient of variation would increase with interval value, even if the sensitivity of an underlying timing mechanism were constant. The model thus reconciled an underlying scalar timing process with obtained behavior, which at first sight violated scalar timing. The model further suggested that different species probably did differ in their underlying timing capacity, as the amount of response generation resulting from nontiming processes would need to be implausibly large to reconcile all the obtained coefficients of variation with an underlying timing process of uniform senstivity.

The basic pattern of activation in motor and sensory temporal tasks: positron emission tomography data

Positron emission tomography (PET) data were obtained from subjects performing a synchronization task (target duration 2700 ms). A conjunction analysis was run to identify areas prominently activated both in this task and in a temporal generalization task (target duration 700 ms) used previously. The common pattern of activation included the right prefrontal, inferior parietal and anterior cingulate cortex, the left putamen and the left cerebellar hemisphere. These areas are assumed to play a major role in time processing, in relation to attention and memory mechanisms.

Changing Sensitivity to Duration in Human Scalar Timing: An Experiment, a Review, and Some Possible Explanations

Evidence from a number of studies of human timing, using temporal generalization and bisection tasks, suggests more sensitive behavioural adjustment to presented durations under conditions in which the timing task demands discriminations between more closely spaced stimuli. An experiment using temporal generalization demonstrated this effect, as discrimination between a 600-msec standard duration and non-standard stimuli both shorter and longer than 600 msec was better when non-standard stimuli were more closely spaced around 600 msec. A review showed similar effects in other temporal generalization tasks and in a number of bisection studies, where time discrimination improved as the ratio of the long and short standards on the bisection task decreased. A standard model of human temporal generalization explained the experimental data in terms of a decrease in the response threshold under more difficult conditions, rather than changes in the representation of the standard duration. On the other hand, data from bisection could be modelled by assuming the contrary; that representations of the short and long standards of the task were more precise under the more difficult conditions. Explanations of some of these effects in terms of attention to duration and/or arousal-induced changes in the speed of an internal clock were discussed.

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.

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.

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. The results conformed well to the linear-type timing consistent with scalar timing theory