Perception of the [m]-[n] distinction in consonant-vowel (CV) and vowel-consonant (VC) syllables produced by child and adult talkers

The contribution of the nasal murmur and vocalic formant transition to the perception of the m]-n] distinction by adult listeners was investigated for speakers of different ages in both consonant-vowel (CV) and vowel-consonant (VC) syllables. Three children in each of the speaker groups 3, 5, and 7 years old, and three adult females and three adult males produced CV and VC syllables consisting of either m] or n] and followed or preceded by i ae u a], respectively. Two productions of each syllable were edited into seven murmur and transitions segments. Across speaker groups, a segment including the last 25 ms of the murmur and the first 25 ms of the vowel yielded higher perceptual identification of place of articulation than any other segment edited from the CV syllable. In contrast, the corresponding vowel+murmur segment in the VC syllable position improved nasal identification relative to other segment types for only the adult talkers. Overall, the CV syllable was perceptually more distinctive than the VC syllable, but this distinctiveness interacted with speaker group and stimulus duration. As predicted by previous studies and the current results of perceptual testing, acoustic analyses of adult syllable productions showed systematic differences between labial and alveolar places of articulation, but these differences were only marginally observed in the youngest children's speech. Also predicted by the current perceptual results, these acoustic properties differentiating place of articulation of nasal consonants were reliably different for CV syllables compared to VC syllables. A series of comparisons of perceptual data across speaker groups, segment types, and syllable shape provided strong support, in adult speakers, for the "discontinuity hypothesis" K. N. Stevens, in Phonetic Linguistics: Essays in Honor of Peter Ladefoged, edited by V. A. Fromkin (Academic, London, 1985), pp. 243-255], according to which spectral discontinuities at acoustic boundaries provide critical cues to the perception of place of articulation. In child speakers, the perceptual support for the "discontinuity hypothesis" was weaker and the results indicative of developmental changes in speech production.