The phonetic integration of speech and non-speech sounds: effects of perceived location.

The third-formant (F3) transition of a three-formant /da/ or /ga/ syllable was extracted and replaced by sine-wave transitions that followed the F3 centre frequency. The syllable without the F3 transition (base) was always presented at the left ear, and a /da/ (falling) or /ga/ (rising) sine-wave transition could be presented at either the left, the right, or both ears. The listeners perceived the base as a syllable, and the sine-wave transition as a non-speech whistle, which was lateralized near the left ear, the right ear, or the middle of the head, respectively. In Experiment 1, the sine-wave transition strongly influenced the identity of the syllable only when it was lateralized at the same ear as the base (left ear). Phonetic integration between the base and the transitions became weak, but was not completely eliminated, when the latter was perceived near the middle of the head or at the opposite ear as the base (right ear). The second experiment replicated these findings by using duplex stimuli in which the level of the sine-wave transitions was such that the subjects could not reliably tell whether a /da/ or a /ga/ transition was present at the same ear as the base. This condition was introduced in order to control for the possibility that the subjects could have identified the syallables by associating a rising or falling transition presented at the left ear with a /da/ or /ga/ percept. Alternative suggestions about the relation between speech and non-speech perceptual processes are discussed on the basis of these results.