Two experiments tested an interval segmentation explanation of duration judgment. In Experiment 1, a 170-sec time interval was filled with 27 unrelated words and three highpriority events (HPEs). These HPEs were clustered at the beginning of the interval (unsegmented condition) or distributed throughout the interval (segmented condition). Both recognition and recall of list information were measured, in addition to duration estimates. While no differences in memory performance were found, duration estimates were greater in the the segmented condition. Experiment 2 also tested the effects of interval segmentation but used 35 words and eight HPEs, a longer clock duration, and also measured the remembered number of events (RNE) in the interval. As in Experiment 1, the segmented condition produced longer duration estimates in the absence of memory performance and RNE differences. A segmentation hypothesis seems a better explanation of these results than previously proposed storage size or amount-of-processing models of duration judgment.Researchers who examine factors affecting psychological duration frequently demonstrate that periods that are "filled" with stimuli are judged to be longer than intervals that are relatively "empty." The "storage size" hypothesis (Ornstein, 1969) is one possible explanation for this phenomenon. According to this metaphor, retrospective duration estimates are based on the quantity of information stored du ring the period and accessible when the duration judgment is made. Other investigators have emphasized the amount of processing or the level of attention required by interval events (Underwood, 1975;Vroon, 1970). The relationship between these variables and time estimates is not always consistent, however. Vroon (1970) has demonstrated that the relationship between amount of processing and duration judgments can be negative or positive, depending upon whether overt responses are required. Regarding the storage size notion, Avant and Lyman (1975) and Block and Reed (1978) have demonstrated differences in judged duration that either are not related or are inversely related to measures of subjects' memory for interval events.The effect of filler events on estimates of duration could also be explained by proposing that fillers are temporal markers that serve to segment experience; a filled interval might therefore seem longer than an empty one, not because of the amount of processing or storage space the intervening events require, but because processing these events generates temporal referents in memory with which to mentally reconstruct the duration of the time period. A very similar notion that focuses on the amount of change experienced du ring the judged interval has recently been proposed and studied by Block and Reed (1978). These experiments dem onstrated that time periods during which subjects performed alternating types of processing were perceived as 77 longer than those during which a single type of processing was performed. These results were interpreted as supporting the...

Predictions based on storage size, processing effort, and change models of time estimation were tested in five experiments. The first of these presented subjects with stimulus patterns that varied on dimensions of sensory-event number and uncertainty. Subjects estimated the duration of time periods using the reproduction method. Duration estimates were most accurately predicted by the number of sensory events in each pattern. This relationship was generally positive, although the specific function relating these variables was dependent upon clock duration. The change model seemed to fit these data best. Experiment 2 demonstrated that the relationship between sensory change and judged duration was not due to the total time of sensory input. Experiments 3, 4, and 5 tested the effects of several different types of change. In Experiments 3 and 4, the number C1f sensory events was held constant, but the regularity of their spatial presentation was varied. In both experiments, duration judgments were positively related to the number of changes that occurred. Because the manipulations used in these experiments produced differences in the visual complexity of stimulus patterns, the argument could be made that storage size or processing effort accounted for the size of duration judgments. Experiment 5 tested the effects of change while holding the visual complexity of stimulus patterns constant. A positive relationship between duration judgments and number of changes was again found. 548Given the ubiquity of man-made clocks in modern societies, it seems clear that humans frequently rely on nonorganismic mechanisms to measure the temporal extent of events. Apart from these timekeeping devices, however, we still experience something metaphorically referred to as "time passage," and can also generate estimates of duration using organismic processes. Although time perception has been the topic of scientific investigation for at least 90 years, a clear understanding of the psychological mechanisms of duration estimation is still forthcoming.Some of the earliest researchers proposed that the experience of duration was based on the output of a biological clock (e.g., Francois, 1927;Hoagland, 1933). Recent models have emphasized the role of cognitive activity rather than metabolic functioning. This cognitive approach has the advantage of being able to explain why the quantity of stimulus information in an interval of clock time can affect its apparent duration. When increasesThe manuscript is based on the first author's doctoral dissertation. Reprint requests should be addressed to W. Douglas

The purpose of this study was to examine individual differences in eye-movement behavior. Six metrics (Fixation Rate, Duration, and Size; Saccade Amplitude; Micro-Saccade Rate and Amplitude) were used to measure individuals' eye-movement behavior profiles (EmBP). We replicate previous research (Andrews & Coppola, 1999; Castelhano & Henderson, 2008) by finding consistent individual differences in fixation duration and saccade amplitude across tasks, and present new findings of stable idiosyncrasies in measures of fixational eye-movement (Fixation Size, Micro-Saccade Rate and Amplitude). Moreover, we observed consistent inter-metric correlations across tasks (e.g., individuals that exhibited relatively high Fixation Rates also presented relative low Micro-Saccade Rates and relatively high Micro-Saccade Amplitudes). Factor Analysis linked the six EmBP metrics together with a single factor, which we speculate might be related to the operational effectiveness of the attentional system, given that individual factor scores were correlated with scores on a self-report measure of attentional function. Normal subjects with relatively high scores on this attention-deficit measure exhibited relatively frequent fixations of short duration and large spatial extent, and relatively infrequent micro-saccades of large amplitude. This EmBP is similar to a general pattern of eye-movement behavior observed with ADHD individuals - difficulty controlling eye movements, maintaining fixation, and inhibiting intrusive saccades. Results of this study indicate that normal individuals exhibit idiosyncratic EmBPs that are quite stable across tasks and are related to attentional ability.

A small difference in the size of the two pupils is common in healthy individuals, a condition termed benign or physiologic anisocoria (BA). Past research indicates that BA is probably caused by asymmetry in sympathetic nervous system (SNS) function [e.g., Rosenberg (2008). Physiologic anisocoria: A manifestation of a physiologic sympathetic asymmetry. Neuro-Ophthalmology, 32, 147-149]. This study is the first to show that BA varies with psychological factors linked to brain asymmetry and autonomic arousal, including gender, attention, and personality. Males exhibited a more directional BA than females, consistent with greater hemispheric lateralization in males. BA also varied with a self-report measure of attentional function, consistent with evidence of hemispheric asymmetry in visuospatial attention networks. Finally, BA varied with personality traits linked to autonomic arousal. Individuals exhibiting higher Meanness and Boldness, and lower Empathy scores tended to show more directional BA. This link between personality traits and BA may be related to brain asymmetries in autonomic arousal and emotion-related processing. If future studies employing direct measures of lateralized brain activity confirm the link between BA and SNS asymmetries, this new metric may prove useful in discovering new relationships between brain organization and psychological function, and how these relationships vary across individuals.

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