Speech Intervention Frameworks in Cantonese-speaking Children and Adolescences With Cleft Palate +/- Lip

Plain-language summary

Cleft Palate ± Lip (CP±L) is one of the most well-known congenital anomalies worldwide. Children and adolescences with CP±L are at high risk of developing speech and communication difficulties due to a range of cleft-related etiologies. Even with timely or early repair of the palate, children with CP±L may still experience cleft-related speech difficulties with a notable proportion of children having continuing velopharyngeal insufficiency (VPI). VPI refers to the presence of incomplete velopharyngeal closure during speech production. Non-articulation parameters of VPI include hypernasality, nasal airflow errors, and grimace, with hypernasality being the hallmark characteristic of VPI. Speech error patterns attributed to continuing VPI may involve what is termed as active compensatory articulatory gestures. For instance, children with cleft palate speech/VPI may have difficulty building up sufficient oral pressure to produce oral targets and may attempt to achieve closure at the level of the glottis resulting in replacement of oral pressure targets with glottal stops or fricatives. The loss of distinctive features and the ability to make meaningful contrasts potentially impacts on global outcomes such as speech understandability and acceptability adversely. In fact, there was still no sufficient evidence to support the efficacy of specific intervention approaches or techniques. Additionally, there are only very few studies that have systematically compared different intervention approaches. Consensus on the effectiveness of different approaches remains inconclusive. It is of vital importance to implement evidence-based speech intervention to achieve the optimal speech and resonance outcomes. Historically, speech intervention approaches can be categorized into motor-phonetic (MP) (+/- principles of motor learning) and linguistic-phonological (LP). Motor-phonetic approaches attempt to modify the phonetic errors individually by explicit instruction of the articulatory movement and extensive amount of practice. Motor-phonetic approaches can be undertaken with or without the application of principles of motor learning, which emphasize intensive practice, optimal task difficulty, and variable practice conditions for better retention and generalization. However, the generalization effect was solely evident for the targeted individual phonemes. Increasingly, cleft palate speech/VPI speech disorder is being viewed as a phonological impairment rather than simply an articulation disorder. Linguistic-phonological approaches, on the other hand, refer to phonological rule-based interventions, which attributes the child's speech sound errors to a disordered internal phonological system. Such approaches, target multiple speech sounds or sound classes, and assumes that there would be generalization across phonemes according to their distinctive features. Examples of LP approaches include the minimal pair approach, maximal oppositions and treatment of the empty set, multiple oppositions and Metaphon. Current evidence has suggested that LP approach resulted in a more superior generalization effects in terms of the speech outcomes within the same class and the overall percentage of speech accuracy. Nevertheless, it is crucial to recognize that these LP approaches still predominantly regard speech as a linear sequence of segments and speech sound errors as a set of rules. Target selection tends to be focused on individual phonemic errors in the children's phonetic repertoire and selected specific phonemes for treatment. In contrast, non-linear phonological (NLP) intervention seeks to capture the complexity of speech sounds organized in a hierarchical structure. It is common to observe a range of phonemes or even classes of phonemes being replaced with a single glottal stop or fricative in cleft palate speech. This results in an extensive collapse of meaningful contrasts in the individual's speech, impacting negatively on speech understandability. As such, target selection in cleft speech intervention would be a critical component for successful treatment outcomes. NLP intervention views a word as a multi-tiered structure and emphasizes the broader nature of the phonological system. With a holistic viewpoint of the speech sound system, the target selection and the treatment direction based on NLP framework would be different. Different research had investigated the use of non-linear phonology in speech intervention. Some of them had revealed the positive outcomes. It is believed that speech intervention guided by non-linear phonology framework would facilitate wider changes in the phonological system of children with cleft palate speech / VPI speech disorder, resulting in a more significant generalization effect and increased overall speech intelligibility. Therefore, the current study would like to investigate the effectiveness of different types speech intervention approaches in children and adolescences with CP±L.

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