On the bistability of sine wave analogues of speech.

Our studies revealed two stable modes of perceptual organization, one based on attributes of auditory sensory elements and another based on attributes of patterned sensory variation composed by the aggregation of sensory elements. In a dual-task method, listeners attended concurrently to both aspects, component and pattern, of a sine wave analogue of a word. Organization of elements was indexed by several single-mode tests of auditory form perception to verify the perceptual segregation of either an individual formant of a synthetic word or a tonal component of a sinusoidal word analogue. Organization of patterned variation was indexed by a test of lexical identification. The results show the independence of the perception of auditory and phonetic form, which appear to be differently organized concurrent effects of the same acoustic cause.

Perceiving the causes of coarticulatory acoustic variation: consonant voicing and vowel pitch.

Coarticulatory acoustic variation is presumed to be caused by temporally overlapping linguistically significant gestures of the vocal tract. The complex acoustic consequences of such gestures can be hypothesized to specify them without recourse to context-sensitive representations of phonetic segments. When the consequences of separate gestures converge on a common acoustic dimension (e.g., fundamental frequency), perceptual parsing of the acoustic consequences of overlapping spoken gestures, rather than associations of acoustic features, is required to resolve the distinct gestural events. Direct tests of this theory were conducted. These tests revealed mutual influences of (1) fundamental frequency during a vowel on prior consonant perception, and (2) consonant identity on following vowel stress and pitch perception. The results of these converging tests lead to the conclusion that speech perception involves a process in which acoustic information for coarticulated gestures is parsed from the stream of speech.