Project Summary/Abstract Children with speech sound disorder (SSD) endure negative social and academic consequences that may mani- fest as life-long personal and professional obstacles if their speech errors are not remediated in a timely manner [1]. Among children with SSD, those with motor involvement are considered the most likely to develop persistent speech errors [2], but there are significant limitations to the means available for measuring the presence of motor involvement. The overall objective of the present proposal is to develop a direct measure of motor involvement while measuring related sensory factors associated with difficulty developing adult-like speech. According to the DIVA theoretical framework, skilled speech production involves using auditory and so- matosensory feedback to guide motor execution [3], which suggests that individual differences in auditory and somatosensory acuity may be relevant for speech-motor outcomes. The current study explores the relative contri- butions of motor execution skill and somatosensory acuity in the development of various phonemes produced by younger and older children. As an index of motor execution skill, we use lingual complexity measures extracted from ultrasound images [4, 5, 6]. As the index of somatosensory skill, we use an oral stereognosis task [7, 8, 9] while controlling for the better-studied variable auditory acuity. The first aim is to establish the relationship between lingual complexity and such indices of articulatory matu- rity as age and disorder status. Our central hypothesis is that lingual complexity will be related with these speech outcomes. That is, based on pilot data showing that lingual complexity is higher in older children than in younger children in productions of the phoneme /r/, we hypothesize that lingual complexity will be higher in older children than in younger children specifically for later-developing phonemes. In addition, based on previous work [6], we hypothesize that lingual complexity will be higher in the correct productions of typically-developing children than in the incorrect productions of children with SSD. The second aim is to understand the relationship between somatosensory acuity and lingual complexity across individuals and to compare somatosensory acuity across groups differing in disorder status. Precision of sensory goals is likely to play a role in an individual's ability to update and fine-tune motor plans [10], so our working hypotheses are that children with high somatosensory acuity will have higher lingual complexity relative to children with low somatosensory acuity and that children with SSD will have higher somatosensory acuity than typically-developing children. Quantification of lingual 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. Understanding the relative contribution of lingual ...