Temporal Patterning of Aerodynamic and Acoustic Events in Apraxia of Speech.

Abstract

The purpose of this investigation was to examine the temporal aspects of speech production and their concomitant affects on the aerodynamic and acoustic events in individuals with apraxia of speech. This study included two normal subjects, three apraxic subjects and one dysarthric subject. The subjects repeated 20 times a CVNCV sequence embedded in a carrier phrase "say p/V/mper in four vowel conditions ( I , ae , a , u ). Differential oral-nasal air pressure, nasal air flow, and acoustic signals were recorded. The size of the velopharyngeal orifice area was also calculated at all the segment durations of the CVNCV sequence were compared with the accompanying differential oral-nasal air pressure and nasal air flow characteristics for the apraxic, dysarthric and normal subjects. Analysis of variance between the apraxic and normal on the acoustic and aerodynamic variables revealed no significant differ- ences. However, within group statistical analysis revealed that the severe apraxic was different when compared to the mild and mod- erate apraxic subjects. Although there were differences between apraxic subjects in the absolute segment and word durations, the severe apraxic speaker demonstrated relative patterns of segmental timing which resembled those temporal patterns of the other apraxic and normal subjects. The dysarthric subjects' relative patterns of segmental timing was different from that of the apraxic. The severe apraxic speaker exhibited greater than normal intra oral air pressures and longer than normal voice onset times. In addition, the calculated velopharyngeal orifice area for the severe apraxic speaker demonstrated a double peak pattern indicative of impaired timing of velopharyngeal behavior. Perceived phonetic errors in the apraxic group were not associ- ated consistently with observed abnormalities in the pressure, flow and acoustic data. The results demonstrate that the severe apraxic subject was able to adjust the relative timing of the speech articulatory mechanism although the absolute acoustic durations were different from the other subjects. These findings are discussed in light of current perceptions of speech motor control.