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 fl ashes (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 d uration of the first stimulus was found to be overestimated by about 5 0%. The illusion was unaffected by stimulus contrast, size, or interfl ash interval (between 100 and 600 ms). For some subjects, the last sti mulus in the train also appeared to be about 50% longer than the penul timate flash. The results are discussed in terms of theories of how at tention, arousal, and stimulus processing can affect duration percepti on. The mechanisms activated are peculiar to the visual system, since no similar illusion of duration was consistently experienced with a tr ain of auditory tones.