This project is designed to answer three questions related to the phonetic representation of children with speech sound production deficits. First, three experimental tasks evaluating aspects of phonetic representation are described. For each task, the performance of 50 preschoolers with speech sound production disorders (hereafter, PD) is compared to that of 50 matched participants, whose speech is age-appropriate. Data also are collected from older children and adults; a cross-sectional design is used to evaluate the significance of age-related trends on each task. The first task assesses acoustic/perceptual space using two procedures: 1) A gating task that systematically limits acoustic information associated with word-final voiceless stop consonants; and 2) A noise-center vowel task, whereby the vocalic nuclei of monosyllabic tokens are systematically replaced by speech-shaped noise. Responses are elicited using nonverbal four-choice closed set picture identification tasks. The second task assesses articulatory/production space. Participants produce a carrier phrase containing three targets with provocalic voiced stop consonants (i.e., bye, die, guy) under two rate conditions: normal and fast. Two sets of three targets with prevocalic voiceless stops also are elicited (i.e., pie, tie, kie; poo, two, coo). Responses will undergo formant slope and spectral burst analyses. The third task assesses mapping between perception and production. A nonword repetition task is used, whereby participants imitate familiar and novel CV, VC, and CC sequences that are embedded in nonsense words. Data from these three tasks are analyzed statistically to evaluate differences between groups and among conditions. Second, intra-group variability among the children with PD is examined. The group of children with PD is divided into subgroups on the basis of language and speech measures. The experimental task performance of the upper quartile is then compared to the lower quartile. Third, the ability of the experimental tasks to differentiate children with PD of different severities from children with age-appropriate speech production skills is examined. Discriminant analysis statistically differentiates half of the children with PD from those who are typically developing. Results are cross-validated using the remaining children. Multiple regression is used to determine the contributions of the three experimental tasks in predicting severity of impairment.
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