Ratio judgments of empty durations with numeric scales

Individual differences in the perception of probability

In recent studies of humans estimating non-stationary probabilities, estimates appear to be unbiased on average, across the full range of probability values to be estimated. This finding is surprising given that experiments measuring probability estimation in other contexts have often identified conservatism: individuals tend to overestimate low probability events and underestimate high probability events. In other contexts, repulsive biases have also been documented, with individuals producing judgments that tend toward extreme values instead. Using extensive data from a probability estimation task that produces unbiased performance on average, we find substantial biases at the individual level; we document the coexistence of both conservative and repulsive biases in the same experimental context. Individual biases persist despite extensive experience with the task, and are also correlated with other behavioral differences, such as individual variation in response speed and adjustment rates. We conclude that the rich computational demands of our task give rise to a variety of behavioral patterns, and that the apparent unbiasedness of the pooled data is an artifact of the aggregation of heterogeneous biases.

Overestimation of the second time interval replaces time-shrinking when the difference between two adjacent time intervals increases

When the onsets of three successive sound bursts mark two adjacent time intervals, the second time interval can be underestimated when it is physically longer than the first time interval by up to 100 ms. This illusion, time-shrinking, is very stable when the first time interval is 200 ms or shorter (Nakajima et al., 2004, Perception, 33). Time-shrinking had been considered a kind of perceptual assimilation to make the first and the second time interval more similar to each other. Here we investigated whether the underestimation of the second time interval was replaced by an overestimation if the physical difference between the neighboring time intervals was too large for the assimilation to take place; this was a typical situation in which a perceptual contrast could be expected. Three experiments to measure the overestimation/underestimation of the second time interval by the method of adjustment were conducted. The first time interval was varied from 40 to 280 ms, and such overestimations indeed took place when the first time interval was 80–280 ms. The overestimations were robust when the second time interval was longer than the first time interval by 240 ms or more, and the magnitude of the overestimation was larger than 100 ms in some conditions. Thus, a perceptual contrast to replace time-shrinking was established. An additional experiment indicated that this contrast did not affect the perception of the first time interval substantially: The contrast in the present conditions seemed unilateral.

Human Processing of Short Temporal Intervals as Revealed by an ERP Waveform Analysis

To clarify the time course over which the human brain processes information about durations up to ∼300 ms, we reanalyzed the data that were previously reported by Mitsudo et al. (2009) using a multivariate analysis method. Event-related potentials were recorded from 19 scalp electrodes on 11 (nine original and two additional) participants while they judged whether two neighboring empty time intervals - called t1 and t2 and marked by three tone bursts - had equal durations. There was also a control condition in which the participants were presented the same temporal patterns but without a judgment task. In the present reanalysis, we sought to visualize how the temporal patterns were represented in the brain over time. A correlation matrix across channels was calculated for each temporal pattern. Geometric separations between the correlation matrices were calculated, and subjected to multidimensional scaling. We performed such analyses for a moving 100-ms time window after the t1 presentations. In the windows centered at <100 ms after the t2 presentation, the analyses revealed the local maxima of categorical separation between temporal patterns of perceptually equal durations versus perceptually unequal durations, both in the judgment condition and in the control condition. Such categorization of the temporal patterns was prominent only in narrow temporal regions. The analysis indicated that the participants determined whether the two neighboring time intervals were of equal duration mostly within 100 ms after the presentation of the temporal patterns. A very fast brain activity was related to the perception of elementary temporal patterns without explicit judgments. This is consistent with the findings of Mitsudo et al. and it is in line with the processing time hypothesis proposed by Nakajima et al. (2004). The validity of the correlation matrix analyses turned out to be an effective tool to grasp the overall responses of the brain to temporal patterns.

Time-shrinking: the process of unilateral temporal assimilation

Our previous research on auditory time perception showed that the duration of empty time intervals shorter than about 250 ms can be underestimated hugely if they are immediately preceded by shorter time intervals. We named this illusion 'time-shrinking' (TS). This study comprises four experiments in which the preceding interval, t1, was followed by a standard interval, t2. When t1 < or = 200 ms, and t1 < or = t2, the underestimation of t2 came into view clearly. The absolute difference between t2 and t1 was the crucial factor for the illusion to appear. The underestimation increased when t2 increased from t1 to t1 + 65 ms, stayed at about 45 ms when t2 was between t1 + 65 ms and t1 + 95 ms, and disappeared suddenly when t2 exceeded t1 + 95 ms. This pattern of results was observed across all values of t1 < or = 200 ms. A model was fit to the data to elucidate the underlying process of the illusion. The model states that the perceived duration difference between t1 and t2 is reduced by cutting mental processing time for t2; in other words, that t2 assimilates to t1.

Imagery and perception-action mediation in imitative actions

This paper describes two lines of research exploring a hypothetical function of imagery in the context of imitative actions: the mediation between perceptual and motor processes. Both experimental approaches, a sequence learning task and a timing imitation task, demonstrate that engagement into imagery as a temporally distinct activity between observation and performance is not required for accurate imitation. Moreover, evidence is provided that generative processes can take place during event observation itself, thus making a separate recoding stage redundant. Nevertheless, in the absence of a visual display, imagery of a movement sequence exerted similar learning effects as physical and observational practice, and visual and motor imagery were found to be equally effective rehearsal strategies for maintenance of temporal information in short-term memory.

Duration illusions in a train of visual stimuli

The first stimulus in a sequential train of identical flashes of light appears to last longer than those in the middle of the train. Four flashes (each 600 or 667 ms) were presented and the first was shortened until it appeared to have the same duration as that of the next. The duration of the first stimulus was found to be overestimated by about 50%. The illusion was unaffected by stimulus contrast, size, or interflash interval (between 100 and 600 ms). For some subjects, the last stimulus in the train also appeared to be about 50% longer than the penultimate flash. The results are discussed in terms of theories of how attention, arousal, and stimulus processing can affect duration perception. The mechanisms activated are peculiar to the visual system, since no similar illusion of duration was consistently experienced with a train of auditory tones.

Auditory isochrony: time shrinking and temporal patterns

It has previously been reported that the duration of short time intervals is conspicuously underestimated if they are preceded by shorter neighbouring time intervals. This illusion was called 'time shrinking' and it was argued that it strongly affects the perception of auditory rhythms. In the present study this supposition has been pursued in three experiments. In the first, temporal patterns consisting of two, three, and four intervals had to be judged for anisochrony, which was invoked by offsetting the last sound from its isochronous position. By a constant method, it was determined that the last sound of fast sequences (50 ms base interval) had to be delayed by about 30 ms in order for isochronous rhythms to be perceived. Another interesting finding was that for sound sequences with base intervals up to 200 ms it was the difference limen, rather than Weber's ratio, that was constant for anisochrony detection. In the second experiment, the temporal patterns comprised two intervals, presented serially or separately. The deviation of isochrony could be on either the first or the second interval. The data, gathered by an adaptive method, showed time shrinking to be effective even up to a base interval of 200 ms. The third experiment involved a constant method and anisochrony was implemented on the first interval of two interval patterns. Time shrinking affected perceived isochrony in sequences with base intervals of 50, 100, and 200 ms. It is argued that the paradoxical results of anisochrony detection can be explained in terms of time shrinking. Some anomalies of rhythm perception and production that are the result of time shrinking are discussed.(ABSTRACT TRUNCATED AT 250 WORDS)