Acoustical analysis of duration differences in the production of nonsense syllables by normal and apraxic speakers

The purpose of this study was to determine if there were differences between normal and apraxic speakers in the durations of selected consonants and vowels. Five normal and five apraxic speakers were presented prerecorded stimuli consisting of the three nonsense disyllables, /paka/, /tapa/, and /kuta/ embedded within the carrier phrase, "You will say ___.” Tape recordings were made as each of the subjects imitatively produced each of the three nonsense disyllables twenty times. The responses were judged for articulatory accuracy, and five productions of each nonsense disyllable for each subject were selected for the duration analyses. The consonant and vowel durations in these utterances were analyzed and measured by use of a digital storage oscilloscope.

The consonant and vowel duration measurements were statistically treated by computing means, standard deviations, and ranges for each speaker as well as for the normal and apraxic groups. The group means, standard deviations, and ranges were compared to determine differences between the groups in consonant and vowel durations. The duration measurements for each apraxic subject also were compared with measures for the normal group to determine whether individual speakers followed the trend evidenced by the group as a whole.

The major findings of this investigation were that the apraxic group consistently demonstrated longer consonant durations than the normal group, particularly for the initial consonants. This trend also was evidenced by each individual apraxic speaker. Further, the results were that the apraxic group consistently exhibited longer vowel durations than the normal group, particularly for the final vowels. This trend often was less apparent among the vowel durations for each individual apraxic subject.

From the results of this study, it may be concluded that there are differences in the durations of selected consonants produced by normal and apraxic speakers. Similarly, there are differences in the durations of selected vowels produced by normal and apraxic speakers. These differences in duration are one aspect of the disturbance of prosody in apraxia of speech, and further research is necessary to determine whether these alterations are compensatory in nature or whether they reflect a primary prosodic disturbance in the disorder.