The development of accuracy in early speech acquisition: relative contributions of production and auditory perceptual factors
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Production system and auditory perceptual factors form a system-based foundation for intelligible speech. The production system contributes motor capacities for producing sounds and sequences. The auditory system provides information about ambient language characteristics of word targets. The child must utilize both to achieve accuracy by matching sounds they can produce with salient word targets. To fully understand the process by which children acquire intelligible speech, we must consider both production system and auditory perceptual factors and how these factors affect behavioral change over time. Acquisition of accuracy for single words was examined in two groups of children differing in auditory history: 4 normal hearing (NH) children and 4 profoundly hearingimpaired children who received cochlear implants (CI) before age 2 years. The developmental process was analyzed via changes in accuracy and error patterns over time. Data was collected monthly in 1-hour recording sessions for 6 months following onset of meaningful words. Words were transcribed with broad phonetic transcription. Consonants and vowels were described by word position and in sequential patterns within and across syllables. viii Segments and sequences produced most frequently were also most accurate across groups and sessions. Lexical targets reflected more diverse phonetic patterns than child production patterns. Both groups performed similarly on all measures except consonant accuracy, where the NH group omitted fewer final consonants. Both groups improved accuracy over time. Consonants changed most dramatically, shifting from omissions in early sessions to correct productions in later sessions. Vowels and consonant-vowel sequences within syllables improved from “partially correct” (i.e., matching some but not all characteristics) to “correct”. Sequences with partial omissions (i.e., isolated vowels) improved to code the correct number of segments within and across syllables. Overall accuracy of segments and sequences in single words increased over the period of the study for both groups. Despite different perceptual histories, they looked very similar in development of early speech accuracy. These findings suggest a stronger influence of the production system than auditory perception on phonetic accuracy in early words, thereby supporting early implantation as a means to achieve speech and language milestones without significant disruption in the process of acquiring accuracy.