Recent research has shown that subdivision of intervals between beats makes the beat tempo seem slower——a "divided time illusion" (DTI) in music. Another temporal illusion described in the psychophysical literature is that a sustained sound seems longer than a silent interval of the same duration. This "sustained sound illusion" (SSI) may be due to acceleration of an internal pacemaker by continuous sound, or it may result from slower perception of sound offsets than of sound onsets. Experiment 1 tested the pacemaker acceleration hypothesis in a rhythmic context by asking musicians to compare or reproduce the tempi of isochronous tone sequences played legato ("filled") or staccato ("unfilled"). There was no indication that legato sequences were perceived as slower than staccato sequences. Experiment 2 tested the delayed offset perception hypothesis by asking musicians to judge the relative time of occurrence of abrupt or decaying tone offsets in the interonset intervals of isochronous sequences. There was no evidence of delayed perception of abrupt offsets, and decaying offsets were perceived only slightly late. These results suggest that the SSI, unlike the DTI, does not occur in rhythmic contexts and thus is probably not of musical relevance. More generally, the results challenge some proposed explanations of this illusion and call for further research on the conditions under which it does occur.
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