Discrimination of empty and filled intervals marked by auditory signals with different durations and directions of intensity change.

A time interval marked by two short sounds ("empty interval") is perceived to be longer when one or more short sounds are inserted within this time interval ("filled interval"). This illusion is known as the filled-duration illusion (FDI), which has been mainly observed above 500 ms. Previous evidence has mostly shown, however, that the FDI within 500 ms is not robust due to individual differences. FDI in this short range has been less influenced by the properties of sound markers (such as amplitude, time duration, and sound energy distribution). I questioned whether the mixed evidence in the short range could be due to the methods and time ranges adopted. Here, I asked whether and how the perceived duration of both the empty interval and the filled interval (a continuous beep) was modulated by markers with different yet short durations, and by markers with intensity changes (ascending vs. descending). The results showed that the longer markers led to more expansion of the perceived time interval than did the short markers. The empty interval (300 ms) was perceived as shorter in the rising intensity (first tone marker)-decreasing intensity (second tone marker) condition, but as longer in the decreasing-decreasing condition. However, the filled interval (300 ms) bounded in the decreasing-decreasing condition was perceived as shorter. Therefore, perception of short empty and filled intervals (enclosed by auditory marks) could be modulated by the temporal properties of the markers. Those findings could be accounted for by the Gestalt perceptual groupings between the auditory markers and the to-be-timed gap/stimulus intervals in an adaptive way.