荒井 隆行

Background : Persistent developmental articulation disorder and language learning impairment are suspected to concur due to a speech processing deficit. The change in children's perceptual strategies is proposed as an indicator of development of speech processing ability (Nittrouer & Miller, 1997b). To diagnose a speech processing deficit and intervene in it early, we examined perceptual weight in an attempt to identify a marker for the development of speech processing ability. Methods : Forty-two native Japanese adults without speech disorder and 2 native Japanese children with persistent developmental articulation disorder and language learning impairment participated the study. They identified tokens from a /∫/-/s/ continuum followed by vocalic portions with formant transitions changing continuously from ones appropriate for /∫/ to those for /s/. Findings : Most adults weighted to the spectrum of the fricative noise more than to formant transition in the same manner as the adults in Nittrouer and Miller. However, as compared with most adults, a small number of adults and the 2 children judged based more on the formant transitions than on the spectrum of the fricative noise like 3- to 4-year-old typically developing children in Nittrouer and Miller. Interpretation : The perceptual weight assigned by adults suggested that they did not perceive uniformly. The perceptual weight assigned by the 2 children indicated that their speech perception ability might develop differently from that of typically developing children because of speech processing deficits.

Classical models of speech recognition assume that a detailed, short-term analysis of the acoustic signal is essential for accurately decoding the speech signal and that this decoding process is rooted in the phonetic segment. This paper presents an alternative view, one in which the time scales required to accurately describe and model spoken language are both shorter and longer than the phonetic segment, and are inherently wedded to the syllable. The syllable reflects a singular property of the acoustic signal - the modulation spectrum - which provides a principled, quantitative framework to describe the process by which the listener proceeds from sound to meaning. The ability to understand spoken language (i.e., intelligibility) vitally depends on the integrity of the modulation spectrum within the core range of the syllable (3-10Hz) and reflects the variation in syllable emphasis associated with the concept of prosodic prominence ("accent"). A model of spoken language is described in which the prosodic properties of the speech signal are embedded in the temporal dynamics associated with the syllable, a unit serving as the organizational interface among the various tiers of linguistic representation.