Children and adults appear to weight some acoustic cues differently in perceiving certain speech contrasts. There are currently two main theories to explain this difference. One of these is Nittrouer and colleagues' Developmental Weighting Shift (DWS) theory, which proposes that children process speech in terms of large units (the size of a syllable or monosyllabic word) while adults process in terms of smaller units [Nittrouer, S. (1992). J. Phon. 20, 351- 382]. This processing difference then impacts on speech perception in terms of the attention that listeners give to acoustic cues. On this view, children are expected to attend more than adults to syllableinternal cues such as vowel-onset formant transitions. An alternative explanation is that adultchild cue weighting differences are due to more general sensory (auditory) processing differences between the two groups. It has been proposed that children may be less able to deal with incomplete or insufficient acoustic information than are adults, and thus may require cues that are longer, louder or more spectrally distinct to identify or discriminate between auditory stimuli [Sussman, J. (2001). J. Acoust. Soc. Am. 109, 1173-1180].
The current study tested these hypotheses in two ways. First, we examined adults' and three- to seven-year-old children's weighting of vowel-onset formant transitions in contrasts in which we systematically varied (i) the consonantal context of the transition: /s/-/sh/, /d/-/b/, /t/-/d/, and /-/m/; and (ii) the spectral distinctiveness of the transition (in terms of the onset frequency, extent, direction and duration of the vowel-onset formant transitions), varying from spectrally distinct (o/-/mo/, /do/-/bo/, and /ta/-/da/) to spectrally similar (i/-/mi/, /de/-/be/, and /ti/-/di/).
Second, we examined adults's and five-year-old children's weighting of vowel-formant offset transitions in phonetically identical withinmonosyllabic- word and across-monosyllabic-word contexts. The transition in question was from the vowel /e/ into a following /b/ or /d/ closure, either within-word: "Abe E" versus "Ade E", or acrossword: "A bee" versus "A dee".
The results of the study showed that adult-child differences in cue weighting are affected by the segmental context of the cues, the salience of the cues, and the position of the cue in the word. However, neither of the above two theories, either on their own or in combination, can account for all of the observed cue weighting behaviour. Possible alternative explanations are discussed.