Subjective shortening with filled and unfilled auditory and visual intervals in humans?

Two experiments tested humans on a memory for duration task based on the method of Wearden and Ferrara (1993), which had previously provided evidence for subjective shortening in memory for stimulus duration. Auditory stimuli were tones (filled) or click-defined intervals (unfilled). Filled visual stimuli were either squares or lines, with the unfilled interval being the time between two line presentations. In Experiment 1, good evidence for subjective shortening was found when filled and unfilled visual stimuli, or filled auditory stimuli, were used, but evidence for subjective shortening with unfilled auditory stimuli was more ambiguous. Experiment 2 used a simplified variant of the Wearden and Ferrara task, and evidence for subjective shortening was obtained from all four stimulus types.