Phonetic perception: evidence for context-dependent and context-independent processing.

In a series of experiments a selective adaptation technique was used to examine the dependencies that arise in processing phonetically relevant acoustic information in syllable-initial consonants. The pattern of results, identical across two vowel contexts, indicated that voice-onset-time specifying a voicing contrast and the spectral form of the initial transitions specifying a place of articulation contrast are processed in a mutually dependent fashion. A different pattern was revealed, however, for the processing of the spectral form of the transitions specifying a place contrast and the duration of the transitions specifying a manner contrast. Specifically, the data indicated that transition duration is processed independently of the spectral characteristics of the transitions, even though the processing of the spectral characteristics of the transitions is dependent on their duration. On the basis of these findings, the following conclusions were drawn: First, there are distinct patterns of interaction during speech processing; second, the system does not operate entirely in a context-conditioned fashion; and third, at early stages of processing the speech signal is not treated holistically, but rather undergoes analysis in terms of those acoustic dimensions that provide information about phonetic distinctions.