Gradient speech change during intervention for school-aged children and adults with cleft palate ± lip

Gradient speech change, where speech sound production develops in a broadly step-wise fashion towards the standard adult form, is a well-recognised phenomenon in children developing typical speech, but is much less studied in speakers with developmental speech sound disorders. Instrumental techniques, such as electropalatography (EPG), may be useful for identifying gradient speech change and may supplement phonetic transcription in important ways. This study investigated whether gradient speech change occurred in six participants with cleft palate ± lip undergoing intervention within a usage-based phonology framework (2/6 participants with speech distortions; 4/6 with pattern-based speech substitutions; combined total of 25 speech sounds targeted for intervention). Participants received weekly therapy in a hospital setting and were aged 10-27 years. Gradient speech change with target speech sounds was examined using EPG analysis, which was undertaken after every fifth session of therapy. The presence of gradient change was determined by visually examining EPG palatograms and EPG indices for target speech sounds across successive EPG test points. This study found gradient speech change occurred in 22/25 target sounds over the course of intervention. This gradient change occurred for both speech distortions and pattern-based speech substitutions. The remaining 3/25 target sounds showed categorical change. Usage-based phonology was suggested as a theory with potential for explaining gradient speech change, with both typical and atypical speech, and with speech distortions and pattern-based speech substitutions. This finding adds to other research showing that the objective data provided by instrumental techniques, such as EPG, may be a valuable complement to phonetic transcription.