Lingual activity in two speech-disordered children's attempts to produce velar and alveolar stop consonants: evidence from electropalatographic (EPG) data.
Research is accumulating to suggest that, in the process of phonological acquisition, children pass through a stage of producing subphonemic acoustic cues to distinguish target phonemic contrasts. These subtle, or covert, distinctions occur unnoticed by a transcriber, yet their existence is viewed as having potentially important theoretical and clinical implications. In this study, the technique of electropalatography (EPG) was used to investigate tongue placement in two speech-impaired subjects (sisters), during their attempts to produce alveolar/velar stop contrasts, and their EPG printouts compared to those of a normal subject. Transcription of the impaired subjects' speech showed that, whilst one was able overtly to produce the contrast, the other was using the phonological process of alveolar backing, and so was judged not to have the contrast. However, contrary to the predictions made based on the auditory transcription, the EPG data revealed that both children were making similar, and clearly distinguishable, lingual-palate contacts for the two places of articulation. Examination of the data revealed that the subject who was overtly producing the contrast was able to control the precise sequence of tongue movements necessary in the release phase of the two classes of stops. This critical stage in alveolar/velar stop production had not been mastered by the subject who was not producing a perceptible distinction. The clinical relevance of these findings is discussed.