Covert contrast and covert errors in persistent velar fronting

Abstract

Acoustic and articulatory studies demonstrate covert contrast in perceptually neutralised phonemic contrasts in both typical children and children with speech disorders. These covert contrasts are thought to be relatively common and symptomatic of phonetic speech disorders. However, clinicians in the speech therapy clinic have had no easy way of identifying this covertness. This study uses ultrasound tongue imaging to compare tongue contours for /t/ and /k/ in seven children with persistent velar fronting. We present a method of overlaying tongue contours to identify covert contrast at the articulatory level. Results show that all seven children, contrary to expectations, produced both /t/ and /k/ with near-identical tongue shapes showing no evidence of covert contrast. However, further analysis of one of the participants showed highly variable tongue shapes for /t/ and /k/, including retroflex productions of both. Although not phonologically conditioned, this covert error is evidence of speech disorder at the phonetic level.

The Impact of Real-Time Articulatory Information on Phonetic Transcription: Ultrasound-Aided Transcription in Cleft Lip and Palate Speech

“…Ultrasound Tongue Imaging (UTI) uses standard medical ultrasound to image the tongue in real-time, making it also suitable for visual biofeedback therapy. Over 30 small studies show it to be effective for treating persistent SSDs (see for example [22] and [25]) and other studies use it for fine articulatory analysis of lingual movements when synchronised to the acoustic signal (for example, [20] or [26]). The ultrasound probe is placed under the chin, capturing most of the surface of the tongue in either the mid-sagittal or coronal plane.…”

“…Both McAllister-Byun, Buchwald and Mizoguchi, [27] and Cleland and colleagues [20] used it to measure covert contrast in children with velar fronting. Cleland and colleagues [20] additionally used it to describe undifferentiated lingual gestures and retroflex articulations (see above).…”

“…Although instrumental techniques do not have the advantages of audio-only phonetic transcription in terms of being easy to use and inexpensive, often the instrumental technique in question is an obvious choice for remediating the child's SSD. For example, Cleland and colleagues [20] report an interesting case of a nine year old child "Rachel" who presented with a particularly persistent case of velar-fronting. Analysis with ultrasound tongueimaging showed that Rachel presented with undifferentiated lingual gestures [21] and retroflexed productions of most stops.…”

Enabling New Articulatory Gestures in Children With Persistent Speech Sound Disorders Using Ultrasound Visual Biofeedback

“…The tongue movement is not separated (entirely) from the somatosensory feedback of articulation, nor from the acoustic consequence, and hence U-VBF adds visual information to what is already multi-modal learning with an articulatory underpinning. In addition to the more explicit and objective information on performance revealed to the speaker, U-VBF can provide the Speech and Language Therapist (SLT) with objective assessment detail that can reveal diagnosticallyuseful covert contrasts and covert errors if the data is recorded and analyzed (Cleland, Scobbie, Heyde, Roxburgh, & Wrench, 2017). Such sub-phonemic behaviors are also evidence of motoric rather than phonological difficulties-a clinically-relevant consideration which further motivates the retention of production data for post-hoc analysis.…”

UltraSuite: A Repository of Ultrasound and Acoustic Data from Child Speech Therapy Sessions

“…The children exhibited a range of SSDs including phonological delay, phonological disorder, inconsistent phonological disorder, vowel disorder, articulation disorder, and childhood apraxia of speech. The data was recorded specifically for the purpose of evaluating the effectiveness of ultrasound as a visual biofeedback tool for therapy [25,26]. Each child attended several sessions: suitability (before baseline), baseline (1-5 sessions), therapy (1-12 sessions), mid-therapy, post-therapy (immediately after therapy), and maintenance (several months after therapy).…”