Establishing the role of sensorimotor skills in speech development and disorders

Abstract

Among children with speech sound disorder (SSD), those with motor involvement are considered the most likely to develop persistent errors, but the means available for measuring motor execution skill are limited. Skilled speech production involves using somatosensory feedback to guide motor execution, which suggests that acuity in this domain may be relevant for speech-motor outcomes. The overall goal of this dissertation is to explore the contributions of motor execution skill and somatosensory acuity in the development of various phonemes produced by younger and older children. To measure motor execution skill, we use tongue shape complexity metrics extracted from ultrasound images; to measure somatosensory skill, we use an oral stereognosis task while controlling for the better-studied variable auditory acuity.

The first aim is to establish the relationship between tongue shape complexity and indices of articulatory maturity. Manuscript 1 lays the foundation for this pursuit by justifying the selection of two tongue shape complexity metrics through an exploration of phoneme-specific patterns in adults and young typically developing children. To test the hypothesis that tongue shape complexity is associated with articulatory maturity, Manuscript 2 asks whether tongue shape complexity is systematically related with age, disorder status, and perceived accuracy for late-developing targets in samples of young children with and without SSD. Manuscript 3 evaluates whether tongue shape complexity is associated with acoustically measured degree of perceived accuracy in a sample of older children undergoing treatment for persistent SSD affecting rhotic targets.

The second aim is to understand the relationship between somatosensory acuity and tongue shape complexity in individuals differing in speech production skill. Using the same sample of older children undergoing treatment for rhotic misarticulation, Manuscript 3 also evaluates whether pre-treatment and post-treatment tongue shape complexity can be predicted from an individual’s somatosensory acuity, while controlling for the better-studied auditory acuity. Quantification of tongue shape complexity in individuals varying in age and clinical profile is a crucial prerequisite for understanding the relative importance of motor factors in children’s non-adult-like speech patterns. Clinically feasible approaches to the measurement of tongue shape complexity and somatosensory skill in children with SSD may help guide clinicians toward treatment approaches that are tailored toward improving skill in these domains.