Tongue shapes for rhotics in school-age children with and without residual speech errors

Abstract

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.

Conflict of interest statement

Statement of Interest: The authors report no conflicts of interest.

Figures

Figure 1:

Examples of undifferentiated (simple), retroflex (moderate), and bunched (complex) tongue shapes for rhotics from the post-training group. Figure 1 note: In each row, circles on the tongue shapes (left) correspond to the inflection point candidates (right, vertical lines) in the unfiltered (black) and trimmed (gray) curvature; dashed lines show inflections having the same sign, ignored in computing the number of inflections (NINFL). The Modified Curvature Index (MCI) is included for comparison.

Figure 2:

Percent of rhotics produced with number of inflections (NINFL) by group

Figure 3:

Mean number of inflections (NINFL) by cluster context and group. Figure 3 note: Error bars show standard error. TYP=Typical speech group, RSE=Residual Speech Error group

Figure 4:

Distribution of perceptual ratings of rhotic accuracy among children with typical speech and children residual speech errors at mid-point of treatment and post-treatment

Figure 5:

Perceptual ratings of rhotic accuracy by Cluster in the Residual Speech Error group at the mid-point of treatment vs. post-treatment. Figure 5 note: Error bars show standard error.