Auditory and phonetic perception of vowels in children with apraxic speech disorders.

The aim of this study was to assess auditory and phonetic perceptual processing of vowels in children with apraxic disorders, who demonstrated clinically with only a speech output deficit. Two experiments were conducted. In the preparatory Experiment 1 series of vowels were constructed by moving formant frequencies away from the extreme values in the vowel space in the direction of a 'neutral-vowel position'. These were presented to adults and children with no speech-language involvement. Based on identification performance low-redundancy vowels were selected, which served as the end-points of two vowel continua: /i/-/i/ and /a/-/a/. In Experiment 2 these continua were used in identification and discrimination tasks, presented to 11 children with apraxic speech problems (aged 6:11 to 9:6 years) and 12 normally developing children. The results showed poorer perception of vowels for the children with apraxic speech problems than for the control children for both continua. Identification functions indicated poorer phonetic processing; discrimination functions indicated poorer auditory processing. Furthermore, a combination of perception measures (identification and discrimination) proved to have a high differential and clinical value for the assessment of children with apraxic speech problems. The results support the view that subtle (subclinical) auditory processing deficits make part of speech output disorders.