Speakers of North American English use variable tongue shapes for rhotic sounds. However, quantifying tongue shapes for rhotics can be challenging, and little is known about how tongue shape complexity corresponds to perceptual ratings of rhotic accuracy in children with residual speech sound errors (RSE). In this study, 16 children aged 9-16 with RSE and 14 children with typical speech (TS) development made multiple productions of 'Let Robby cross Church Street'. Midsagittal ultrasound images were collected once for children with TS and twice for children in the RSE group (once after 7 h of speech therapy, then again after another 7 h of therapy). Tongue contours for the rhotics in the four words were traced and quantified using a new metric of tongue shape complexity: the number of inflections. Rhotics were also scored for accuracy by four listeners. During the first assessment, children with RSE had fewer tongue inflections than children with TS. Following 7 h of therapy, there were increases in the number of inflections for the RSE group, with the cluster items cross and Street reaching tongue complexity levels of those with TS. Ratings of rhotic accuracy were correlated with the number of inflections. Therefore, the number of inflections in the tongue, an index of tongue shape complexity, was associated with perceived accuracy of rhotic productions.
Keywords: Rhotic; children; speech sound disorder; tongue; ultrasound.