Visualising speech: identification of atypical tongue-shapes in cleft lip and palate using ultrasound

Background: Speech is of key importance in cleft lip and palate (CLP) from a quality of life and surgical outcome perspective, yet assessment relies on subjective perceptual methods. CLP speech is known to be vulnerable to imperceptible error types, such as double articulations which can only be identified with instrumental techniques. Previous research by Gibbon (2004) shows that at least eight distinct error types can be identified in CLP using electropalatography (EPG). However, EPG is expensive and logistically difficult. In contrast, ultrasound is cheaper and arguably better equipped to image the posterior articulations (such as pharyngeals) which are common in CLP.

Purpose: To develop an ultrasound-based diagnostic assessment for identifying imperceptible speech errors in children with cleft palate. Research questions were: 1. Which of the eight CLP error types can be visualised and quantified with ultrasound measures? 2. Does ultrasound assessment confirm or refute perceptual evaluation?
Method: Thirty children aged 3 to 18 with CLP were recorded with simultaneous audio and probe-stabilised ultrasound during spontaneous counting, elicitation of all consonants in /aCa/, and sentences from GOS.SP.ASS. 98. Two types of analyses were performed: 1. Phonetic transcription to identify overt speech errors; 2. Ultrasound analysis to identify auditorily imperceptible errors. The ultrasound analysis was further subdivided into real-time qualitative observations from ultrasound (to identify e.g. double articulations, pharyngeal stops); and quantitative ultrasound analysis using a variety of measures from the literature (e.g. Dorsum Excursion Index to identify increased contact).

Results: Results of the phonetic transcription show a range of typical (normalised) speech, compensatory articulations, and developmental errors, consistent with the literature. Qualitative analysis in most cases confirms the perceptual analysis but provides additional information about imperceptible errors including those previously reported by Gibbon (2004) such as double articulations and errors not previously reported in the EPG literature such as retroflexed productions.
Conclusions: Ultrasound Tongue Imaging shows promise as clinically useful diagnostic tool for speech disorders associated with CLP.