Children with Childhood Apraxia of Speech (CAS) are highly likely to experience difficulties producing vowels. Indeed, vowel errors have been mentioned as a potential diagnostic marker for the disorder. Vowel errors are also significant because they have a direct impact on intelligibility and can have serious consequences for consonant production. For these reasons, it is important that speech-language pathologists recognise and address any vowel difficulties that occur in a childs speech.
Despite their importance, assessment and treatment of vowel errors in CAS are particularly challenging activities. Although SLPs are often skilled at detecting vowel errors, they can nevertheless be difficult to hear and transcribe reliably. One reason for this is the fact that normal dialectal differences in vowel systems make listeners more tolerant of abnormal variations in vowel productions. Therapy that focuses on vowels can also be problematic. Any therapy approach that requires a child to focus on his or her own articulatory activity is more difficult with vowels than it is with consonants. The high degree of vocal tract constriction involved in consonant production generally results in a high level of tactile feedback, which enhances speakers awareness of articulatory placement. With the exception of close vowels, such as the vowels in “heat” and “hit”, this tactile feedback is greatly decreased during vowel production.
Vowels may be affected in a variety of ways in CAS. A difficulty in positioning and sequencing of articulators, particularly the tongue and lips, is a well-documented spatial feature of CAS. Incorrect positioning of the lips and tongue will affect vowel quality and accuracy. Timing difficulties can also affect vowels, so that in some cases they may be excessively long. Vowels may also be produced as distortions. For example, they may be only partially voiced due to difficulties controlling vocal fold vibration or have excessive nasality due to difficulties controlling velopharyngeal closure. These spatial, temporal and co-ordination difficulties are core features of CAS and can often cause difficulties that affect vowels in these children.
Clinical assessment of vowels in CAS is usually based on phonetically transcribed speech samples, which the SLP will analyse and interpret alongside other routine clinical examinations. The samples usually include spontaneous speech, single words/phrases of increasing phonetic complexity elicited through picture naming, and imitated productions of words. Analysis of speech samples may involve identifying a childs vowel inventory. This is a list of the different vowel sounds that a child can make, regardless of whether they are correct or errors. The vowel inventory in CAS may be restricted, with certain difficult to produce vowels, such as diphthongs and r-coloured vowels, absent. Assessment may also include identifying error patterns of vowel substitutions, distortions and phonological processes. These patterns allow the SLP to detect whether phonological rules govern the occurrence of vowel errors and to compare a child’s pronunciations with an adults correct productions and with typically developing young childrens productions. Another aspect to be assessed is the nature and degree of variability in vowel production. There is often a high degree of variability, with more errors in longer words, phrases and in unstressed syllables. A final area to assess is the effect of surrounding consonants on vowel accuracy. Vowels may be produced correctly in some words, but not others because they are conditioned by the surrounding consonants. These analyses will allow the SLP to make a diagnostic statement about a childs vowel production, and to formulate goals of therapy in relation to any vowel difficulties.
At the moment there is a lack of research evidence to guide the SLP about the most efficacious therapy approach for vowel errors in CAS. To take an example, we do not know whether maximum benefits are gained from targeting vowels directly, or whether therapy that focuses on improving the consonant system has an indirect, but equally beneficial, effect of improving the vowel system. At present our evidence is based on speculation and rather limited observations of single children or small groups of children, and we need to improve this evidence by conducting systematic studies of larger populations using rigorous experimental methods. As we await further research, SLPs can be creative in adapting the many therapy approaches that have been designed and proved to be efficacious for consonant errors (see Gibbon and Mackenzie Beck, 2002). Clinicians can select therapy techniques based on the most complementary matching between a childs specific speech difficulties and the strategies employed in a particular approach. In many cases, different approaches are not mutually exclusive, and the SLP will often select a combination of multisensory techniques that will meet each childs specific needs.
Gibbon, F.E and J. Mackenzie Beck. “Therapy for Abnormal Vowels in Children with Phonological Impairment.” Vowel Disorders. Eds. M.J. Ball and F.E Gibbon. Butterworth-Heinemann, 2002. 217-248.
(Fiona Gibbon, Ph.D., is Reader in Speech and Language Sciences at Queen Margaret University College, Edinburgh, Scotland. Her areas of teaching and research interests include the clinical applications of speech science, childhood apraxia of speech, specific language impairment, phonological disorders, cleft palate and autism. She has presented over 100 conference papers at local, national, and international levels and has published more than 70 scientific papers and book chapters. In 2002 she edited in collaboration with Professor Martin Ball the first book to be published on vowel disorders. Dr. Gibbon was an invited presenter at the 2002 Childhood Apraxia of Speech Symposium cosponsored by The Hendrix Foundation and CASANA, and her work has recently been included in a prestigious national award, the 2002 Queens Anniversary Prize, for excellence and innovation in research and teaching.)