Auditory and linguistic processes in speech perception: Inferences from six fusions in dichotic listening.

A number of phenomena in speech perception have been called fusion, but little effort has been made to compare these phenomena in a systematic fashion. The present paper examines six of them. All can be exemplified using the syllable /da / as in dot, and all occur during dichotic listening. In each type of fusion, the robustness of the fused percept is observed against variation in three parameters: the relative onset time of the two opposite-ear stimuli, their relative intensity, and their relative fundamental frequency. Patterns of results are used to confirm the arrangement of the six fusions in a hierarchy, and supporting data are summoned in an analysis of the mechanisms that underlie each with reference to speech. The six fusions are sound localization, psychoacoustic fusion, spectral fusion, spectral/temporal fusion, phonetic feature fusion, and phonological fusion. They occur at three, perhaps four, different levels of perceptual analysis. The first two levels are characterized by per-ceptual integration, the other (s) by perceptual disruption and recombination. Many accounts of speech and language em-phasize a hierarchical structure (see, e.g., Fry, 1956; Pisoni, in press; Studdert-Kennedy, 1974, in press). Recently, the interface be-tween two particular levels in this hierarchy has aroused much attention: the general level logically just prior to linguistic analysis, typ-ically called the auditory level, and the first tier of the language hierarchy logically just subsequent to that auditory analysis, the