Effects of deviation from isochronism on the durational shrinkage by noise replacement

Abstract

The duration of sounds generally tends to be perceived as shorter when a portion is replaced by a noise burst. However, a reversal/prolongation tendency can occur if a compelling isochronous context is functioning. To test the robustness of the durational shrinkage as well as to investigate what aspect is the core feature providing the isochronism, three experiments are conducted using (1) a non-isochronous sequence of four tones, (2) a four-tone sequence whose interonset intervals fluctuate randomly, and (3) a four-tone sequence whose interonset intervals are fixed to be isochronous irrespective of adjustment by human participants in the experiment. In most cases, the noise replacement causes the perceived duration of the target tone to shrink compared to that of its intact counterpart. Furthermore, the reduction of isochronous context results in the reduction of the reversal tendency, although the shrinking effect cannot be observed clearly either. The effects of noise replacement and context are discussed in relation to the contribution of local cues provided by the perceptual evidence as well as the contribution of a global cue provided by an isochronous interonset interval.