Covert contrast and covert errors in persistent velar fronting

Area of Science:

• Speech-language pathology
• Phonetics
• Child language acquisition

Background:

• Covert contrast, or subtle articulatory differences in speech sounds, is often found in children with speech disorders.
• Identifying covert contrast is challenging for speech-language pathologists in clinical settings.
• Persistent velar fronting is a common speech sound disorder in children.

Purpose of the Study:

• To investigate the presence of covert contrast for /t/ and /k/ sounds in children with persistent velar fronting.
• To evaluate the utility of ultrasound tongue imaging for identifying articulatory-level covert contrast.
• To compare tongue contours of /t/ and /k/ in children with speech disorders.

Main Methods:

• Ultrasound tongue imaging was used to capture tongue contours.
• Tongue contours for /t/ and /k/ were compared in seven children with persistent velar fronting.
• A novel method of overlaying tongue contours was employed to detect articulatory differences.

Main Results:

• All seven children produced /t/ and /k/ with nearly identical tongue shapes, showing no evidence of covert contrast.
• Further analysis of one participant revealed highly variable tongue shapes for both /t/ and /k/, including retroflex productions.
• The observed variability in one child, though not phonologically conditioned, indicated a phonetic-level speech disorder.

Conclusions:

• The study challenges the assumption that covert contrast is always present in perceptually neutralised phonemic contrasts in children with speech disorders.
• Ultrasound imaging provides a method for articulatory analysis, but covert contrast was not consistently found in this cohort.
• Atypical articulatory variability, even without clear covert contrast, can be indicative of a phonetic speech disorder requiring clinical attention.