Temporal bisection is influenced by ensemble statistics of the stimulus set

Although humans are well capable of precise time measurement, their duration judgments are nevertheless susceptible to temporal context. Previous research on temporal bisection has shown that duration comparisons are influenced by both stimulus spacing and ensemble statistics. However, theories proposed to account for bisection performance lack a plausible justification of how the effects of stimulus spacing and ensemble statistics are actually combined in temporal judgments. To explain the various contextual effects in temporal bisection, we develop a unified ensemble-distribution account (EDA), which assumes that the mean and variance of the duration set serve as a reference, rather than the short and long standards, in duration comparison. To validate this account, we conducted three experiments that varied the stimulus spacing (Experiment 1), the frequency of the probed durations (Experiment 2), and the variability of the probed durations (Experiment 3). The results revealed significant shifts of the bisection point in Experiments 1 and 2, and a change of the sensitivity of temporal judgments in Experiment 3—which were all well predicted by EDA. In fact, comparison of EDA to the extant prior accounts showed that using ensemble statistics can parsimoniously explain various stimulus set-related factors (e.g., spacing, frequency, variance) that influence temporal judgments.

The psychophysics of visual search with heterogeneous distractors

Visual search is one of the most ecologically important perceptual task domains. One research tradition has studied visual search using simple, parametric stimuli and a signal detection theory or Bayesian modeling framework. However, this tradition has mostly focused on homogeneous distractors (identical to each other), which are not very realistic. In a different tradition, Duncan and Humphreys (1989) conducted a landmark study on visual search with heterogeneous distractors. However, they used complex stimuli, making modeling and dissociation of component processes difficult. Here, we attempt to unify these research traditions by systematically examining visual search with heterogeneous distractors using simple, parametric stimuli and Bayesian modeling. Our experiment varied multiple factors that could influence performance: set size, task (N-AFC localization vs detection), whether the target was revealed before or after the search array (perception versus memory), and stimulus spacing. We found that performance robustly decreased with increasing set size. When examining within-trial summary statistics, we found that the minimum target-to-distractor feature difference was a stronger predictor of behavior than the mean target-to-distractor difference and than distractor variance. To obtain process-level understanding, we formulated a Bayesian optimal-observer model. This model accounted for all summary statistics, including when fitted jointly to localization and detection. We replicated these results in a separate experiment with reduced stimulus spacing. Together, our results represent a critique of Duncan and Humphrey’s descriptive approach, bring visual search with heterogeneous distractors firmly within the reach of quantitative process models, and affirm the “unreasonable effectiveness” of Bayesian models in explaining visual search.

Is a Multi-Slider Interface Layout Responsible for a Stimulus Spacing Bias in the MUSHRA Test?

The multi-stimulus test with hidden reference and anchors (MUSHRA) is commonly used for subjective quality assessment of audio systems. Despite its wide acceptance in scientific and industrial sectors, the method is not free from bias. One possible source of bias in the MUSHRA method may be attributed to a graphical design of its user interface. This paper examines the hypothesis that replacement of the standard multi-slider layout with a single-slider version could reduce a stimulus spacing bias observed in the MUSHRA test. Contrary to the expectation, the aforementioned modification did not reduce the bias. This outcome formally supports the validity of using multiple sliders in the MUSHRA graphical interface.

Stimulus Range 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.