The filled-duration illusion: limits of duration of interval and auditory fillers

Two experiments were conducted to explore parameters of the filled-duration illusion, i.e., intervals filled with stimuli are perceived as longer than empty intervals of equal physical duration. It was hypothesized that the illusion would be found only for intervals of short duration, i.e., a few seconds, and that filled intervals would vary in perceived duration as a function of the type of "filler." Auditory tones were used as boundary and filler stimuli in a counterbalanced (Exp. I) and randomized (Exp. II) design that covered 9 intervals ranging from 1 to 60 sec. A psychophysical method of verbal estimation with single stimuli was employed. The first hypothesis was supported in that only with the short intervals (1 and 3 sec.) was there any evidence of a filled-duration illusion. The type of filler stimulus was important only in the 1-sec. intervals. Results are interpreted in terms of information-processing models for time perception.