Contextual effects in interval-duration judgements in vision, audition and touch

We examined the effect of temporal context on discrimination of intervals marked by auditory, visual and tactile stimuli. Subjects were asked to compare the duration of the interval immediately preceded by an irrelevant "distractor" stimulus with an interval with no distractor. For short interval durations, the presence of the distractor affected greatly the apparent duration of the test stimulus: short distractors caused the test interval to appear shorter and vice versa. For very short reference durations (a parts per thousand currency sign100 ms), the contextual effects were large, changing perceived duration by up to a factor of two. The effect of distractors reduced steadily for longer reference durations, to zero effect for durations greater than 500 ms. We found similar results for intervals defined by visual flashes, auditory tones and brief finger vibrations, all falling to zero effect at 500 ms. Under appropriate conditions, there were strong cross-modal interactions, particularly from audition to vision. We also measured the Weber fractions for duration discrimination and showed that under the conditions of this experiment, Weber fractions decreased steadily with duration, following a square-root law, similarly for all three modalities. The magnitude of the effect of the distractors on apparent duration correlated well with Weber fraction, showing that when duration discrimination was relatively more precise, the context dependency was less. The results were well fit by a simple Bayesian model combining noisy estimates of duration with the action of a resonance-like mechanism that tended to regularize the sound sequence intervals.