Short-term memory for time intervals

The effect of intertrial interval, preset interval, and retention interval on the performance of rats in a time estimation task was described. On each trial a signal was presented for a duration of 2 to 8 sec. Eighteen rats were trained to press one lever (the short response) if the signal was shorter than 4 sec, and another lever (the long response) if the signal was longer than 4 sec. When trials were massed (Experiment 1), the percentage long response was affected by the classification of the previous signal, but not by its actual duration. This suggests that the animals remembered the response made on the previous trial, but not the signal duration. If a response was not permitted on the previous trial (Experiment 2), the duration or classification of the previous signal had no effect on performance. This supports the conclusion from the first experiment and suggests that an animal can reset its internal clock in less than 2 sec. In Experiment 3, the difference limen of the psychophysical function increased with the duration of the retention interval, but the point of subjective equality did not change. This suggests that resetting of the internal clock occurs on a non-time dimension.     

Image memorability across longer time intervals

You may find some images easier to remember than others. Recent studies of visual memory have found remarkable levels of consistency for this inter-item variability across observers, suggesting that memorability can be considered an intrinsic image property. The current study replicated and extended previous results, while adopting a more traditional visual long-term memory task with retention intervals of 20 min, one day, and one week, as opposed to the previously used repeat-detection task, which typically relied on short retention intervals (5 min). Our memorability rank scores show levels of consistency across observers in line with those reported in previous research. They correlate strongly with previous quantifications and appear stable over time. Furthermore, we show that the way consistency of memorability scores increases with the number of responses per image follows the Spearman–Brown formula. Interestingly, our results also seem to show an increase in consistency with an increase in retention interval. Supported by simulated data, this effect is attributed to a decrease of extraneous influences on recognition over time. Finally, we also provide evidence for a log-linear, rather than linear, decline of the raw memorability scores over time, with more memorable images declining less strongly.     

Discrimination of visually perceived intervals of time

The discrimination of short intervals of time, demarcated by a foveally presented spatially distinct double pulse of light, was studied under several conditions of pulse intensity, angular diameter, and duration. We defined temporal acuity as a measure of discrimination capacity in terms of d′ values. It is shown that the acuity mechanism uses largely integrated information—in the spatial and temporal domain, up to at least 56′ and 32 msec, respectively. Acuity increases slightly with increasing integrated pulse energy, but seems quite independent of the presence of an adapting field of appreciable brightness. Studies on the effect of the foveal site aimed at by the pulses of light have shown that temporal projections lead to significantly poorer acuity values than nasal projections. Monoptic and dichoptic stimulation, however, are fully equivalent.     

Pace alteration and estimation of time intervals

This experiment examined the effects on participants' estimates of interval duration of altering the pace of auditory stimuli contained within "filled" intervals. Because most previous studies on the filled interval effect have utilized visual displays, auditory stimuli were used to assess whether the effect would be present. In addition, previous studies compared two intervals, one of which was filled and the other unfilled. In the present study, both intervals were filled with tones at one of three rates (or "paces"): slow, medium, or fast. 25 participants (20 women) ages 18 to 29 years (M = 20.4, SD = 2.3) were recruited from psychology courses and programs. Participants first heard a "training" interval filled with tones at one of the three paces and then attempted to reproduce the duration of that training interval in the "test" interval. The pace of stimuli in each pair of training and test intervals was varied so participants received all possible combinations of paces of auditory stimuli during the training and test trial sets. Analysis showed that, when training pace was fast and test pace was medium or slow, participants' estimates were longer than the actual test interval durations. Conversely, when training pace was slow and test pace was medium or fast, participants' estimates were shorter than actual test interval durations. In addition, when judging shorter intervals, participants estimated more time had passed than actually had, while they estimated that less time had passed than actually had for longer intervals, thus providing support for Vierordt's law.     

Contrast influences perceived duration of brief time intervals

34 participants judged the duration of a 4-sec. interval which was preceded by a contextual interval of 2, 6, 10, or 14 sec. Underestimations of the test interval when the contextual intervals were longer suggested temporal durations are affected by a mechanism of comparing and contrasting analogous to the one producing some visual illusions.     

The lifespan of time intervals in reference memory

To further explore how memory influences time judgments, we conducted two experiments on the lifespan of temporal representations in memory. Penney et al (2000, Journal of Experimental Psychology Human Perception and Performance 26 1770-1787) reported that the perceived duration of auditorily and visually marked intervals differs only when both marker-type intervals are compared directly. This finding can be explained by a 'memory-mixing' process, whereby the memory trace of previous intervals influences the perception of upcoming ones, which are then added to the memory content. In the experiments discussed here, we manipulated the mixing mode of auditory/visual signal presentations. In experiment 1, signals from the same modality were either grouped by blocks or randomised within blocks. The results showed that the auditory/visual difference decreased but remained present when modalities were grouped by blocks. In experiment 2, we used a line-segmentation task. The results showed that, after a training block was performed in one modality, the perceived duration of signals from the other modality was distorted for at least 30 trials and that the magnitude of the difference decreased as the block went on. The results of both experiments highlight the influence of memory on time judgments, providing empirical support to, and quantitative portrayal of, the memory-mixing process.     

Discrimination of time intervals bounded by tone bursts

Trained listeners had to discriminate, in a four-level 2AFC paradigm, the duration of a time interval bounded by pairs of brief tone bursts. The time intervals ranged from 10 to 100 msec. When the tone-burst markers were similar in their intensity (86 dB SPL) and frequency (1 kHz), the just noticeable time difference was found to be monotonically related to the base interval. On the other hand, when the intensity of the first marker was severely attenuated (by 50 dB) or when a large (2-octave) difference was introduced between the frequencies of the two markers, the time discrimination functions became nonmonotonic. A similar, albeit slight, departure from monotonicity was also achieved by making the second marker much longer than the first (300 msec vs. 10 msec). The nonmonotonicity of these time discrimination functions is compared to the well-documented nonmonotonicity that may be observed for voice onset time (VOT) discrimination functions.     

The indifference argument

I argue against motivational internalism. First I recharacterise the issue over moral motivation. Second I describe the indifference argument against motivation internalism. Third I consider appeals to irrationality that are often made in the face of this argument, and I show that they are ineffective. Lastly, I draw the motivational externalist conclusion and reflect on the nature of the issue. Thanks for helpful comments to Philippa Foot and especially to an anonymous referee. Distant ancestors of the paper were given as talks in an American Philosophical Association conference in New Orleans and in St Andrews.     

Perception of acoustically presented time series with varied intervals

Data from three experiments on serial perception of temporal intervals in the supra-second domain are reported. Sequences of short acoustic signals (“pips”) separated by periods of silence were presented to the observers. Two types of time series, geometric or alternating, were used, where the modulus 1 + δ of the inter-pip series and the base duration T_b (range from 1.1 to 6 s) were varied as independent parameters. The observers had to judge whether the series were accelerating, decelerating, or uniform (3 paradigm), or to distinguish regular from irregular sequences (2 paradigm). “Intervals of subjective uniformity” (isus) were obtained by fitting Gaussian psychometric functions to individual subjects' responses. Progression towards longer base durations (T_b = 4.4 or 6 s) shifts the isus towards negative δs, i.e., accelerating series. This finding is compatible with the phenomenon of “subjective shortening” of past temporal intervals, which is naturally accounted for by the lossy integration model of internal time representation. The opposite effect observed for short durations (T_b = 1.1 or 1.5 s) remains unexplained by the lossy integration model, and presents a challenge for further research.     

Judgment of short time intervals while performing mathematical tasks

Ornstein (1969) suggested that the apparent duration of a time interval depended upon the memory storage size. This experiment tests this theory by studying duration estimates made while performing different types of information processing. Twenty Ss, introductory psychology students, served in each of the 30 conditions of the experiment. The six time intervals estimated by the method of reproduction were of lengths of 10, 12, 14, 16, 18, and 20 sec, and the five intervening tasks were doing nothing, reading numbers, adding, multiplying, and adding and multiplying in a random order. The results show that fewer items were output in the three arithmetic conditions, as compared with the reading condition, and also show that the duration estimates were shorter for these three conditions. Estimates of duration are related to amount of output, and also appear to be related to the type of processing done to produce this output.     

Information processing and estimation of short time intervals.

Duration estimates were assessed by the method of reproduction with filled reproduction intervals. Mental arithmetic, reading and mirror-image drawing were used in pairs as initial and/or reproduction tasks. All nine possible pairs of tasks were used in a 9 X 5 X 5 mixed design with five Ss per task pair and five interruption intervals for each initial task. Results indicated that, when arithmetic was used as the initial task, Ss underestimated the duration of the initial interval. When arithmetic was used as the reproduction task, Ss overestimated the duration of the initial interval. A significant correlation was obtained between arithmetic outputs and the lengths of the duration estimates. Results are interpreted as supportive of Burnside's (1971) interpretation of Ornstein's (1969) storage-size hypothesis.     

From indifference to goodness

In this paper, delivered as the 1995 Philip Hallie Memorial Lecture at Wesleyan University's College of Letters, the author reflects on Hallie's philosophical legacy and introduces clinical pragmatism as a method for moral problem-solving in medicine and medical ethics. director of medical ethics at The New York Hospital, and associate for medicine at the Hastings Center.     

Hedonic arousal, time intervals, and excitation transfer

Zillmann’s (1978, 1983) excitation transfer theory was tested in relation to arousal processes opposite in hedonic valence. Sixty female subjects, randomly assigned to six experimental conditions, were initially exposed either to arousal stimulation positive in hedonic valence (sexual humor), or to arousal stimulation negative in hedonic valence (insulting remarks), or to a neutral unarousing task. In each condition, half of the subjects rated mildly arousing positively valenced male models’ photographs on several scales either immediately or with a 4 minute delay following prior arousal. In support of Zillmann’s theory, subjects in the positive hedonic arousal condition gave significantly lower photograph ratings on the arousal-related scales at the immediate, than at the delayed, rating time. However, contrary to Zillmann’s theory, the pattern of these ratings was reversed in the negative hedonic arousal condition, with the significantly higher ratings at the immediate, rather than delayed, rating time. Also, there were significant differences in these ratings among all three conditions both at the immediate and at the delayed rating time, but, as predicted, no significant differences were obtained for these ratings between the rating times in the control unarousing condition. The differences in excitation transfer between arousal processes positive and negative in hedonic valence may be due to their differences on a temporal dimension with regard to the speed of accumulation and the speed of dissipation of each arousal type.     

Pigeons group time intervals according to their relative duration

In the present research, we asked whether pigeons tended to judge time intervals not only in terms of their absolute value but also relative to a duration from which they must be discriminated (i.e., longer or shorter). Pigeons were trained on two independent temporal discriminations. In one discrimination, sample durations of 2 and 8 sec were associated with, for example, red and green hue comparisons, respectively, and in the other discrimination, sample durations of 4 and 16 sec were associated with vertical and horizontal line comparisons, respectively. If pigeons are trained on a temporal discrimination and tested with intermediate durations, the subjective midpoint typically occurs close to the geometric mean of the two trained values. The 4- and 8-sec values were selected to be the geometric mean of the two values in the other discrimination. When a 4-sec test sample was presented with the comparisons from the 2- and 8-sec discrimination, the pigeons preferred the comparison associated with the shorter sample. Similarly, when an 8-sec test sample was presented with the comparisons from the 4-and 16-sec discrimination, the pigeons preferred the comparison associated with the longer sample. Thus, a relative grouping effect was found. That is, durations that should have produced indifferent choice were influenced by their relative durations (shorter than or longer than the alternative) during training.     

Judging the relative duration of multimodal short empty time intervals

Three experiments address the cause of the different performance levels found in time discrimination of empty intervals with durations near 250 msec. Performance differed according to the kind of sensory modality that marked the intervals. With a procedure in which the type of marker was randomized from trial to trial, it was shown that variability of discrimination judgments could not be attributed entirely to the variability of the criterion on which a judgment was based. Such a randomization slightly affects discrimination but provokes a reorganization related to marker conditions of the probabilities of judging an interval to be short or long. Moreover, it was shown that within intramodal conditions, physical characteristics of markers influence the discrimination performances. To account for the results generated with different marker-type intervals at 250 msec, we propose that two types of processor may be involved in duration discrimination: one is specifically related to a given sensory modality, whereas the other is aspecific and responsible for discrimination of intermodal intervals.     

Variations in perception of short time intervals during menstrual cycle

The hypothesis that women experience heightened sensitivity and responsivity premenstrually was tested by asking 10 women to produce short time intervals at four phases of the menstrual cycle. 10 men were assigned to "pseudo-cycles" and tested as a control. The test was based on the assumption that a greater sensitivity to stimuli is reflected in a "slowing down" of subjective time. The women produced the shortest time intervals three to four days before menses, confirming the hypothesis.