A kinematic investigation of anticipatory lingual movement in acquired apraxia of speech

Background: Apraxia of speech (AOS) is considered a disorder of speech planning or programming. Evidence for this stems from perceptual, acoustic, and electropalatographic investigations of articulation in AOS that revealed a delayed onset of anticipatory vowel gestures. Articulatory prolongation and syllable segregation have been attributed to a disturbance in anticipatory coarticulation. Aims: The aim of the current study was to investigate anticipatory lingual movement for consonantal gestures in AOS, and its impact on absolute and relative speech timing. Methods Procedures: Tongue-tip movement and tongue-to-palate contact patterns were recorded for three speakers with AOS and a concomitant aphasia (age range = 35-63 years; M = 50.67 years; SD = 14.29) and five healthy talkers (age range = 29-65 years; M = 52.6 years; SD = 14.5) during the phrases oa scarleto and oa sergeanto, using electromagnetic articulography (EMA) (AG-200 system) and electropalatography (EPG) (Reading Electropalatograph system). Anticipatory lingual movement and speech timing were analysed during the final C1VC/C2 syllable in each of these phrases, where C represented an alveolar or postalveolar consonant. Specifically, tongue-tip displacement was calculated from the onset of release to the end of release of C1 to provide an indication of anticipatory lingual movement. With respect to speech timing, absolute (i.e., duration from time of maximum contact for C1 to time of maximum contact for C2) and relative (i.e., absolute duration expressed as a function of total syllable duration) durational measures were recorded, as was the stability of each. The results recorded for each of the participants with AOS were individually compared to those obtained by the control group. Outcomes Results: The EMA results indicated that two participants with AOS exhibited reduced anticipatory lingual movement (i.e., greater tongue-tip displacement) during repetitions of osergeanto; however, all speakers produced a comparable tongue-tip displacement to that produced by the control group during the release of /l/ in oscarleto. The EPG results indicated that absolute duration was significantly prolonged during the final syllables of both stimuli for each of the apraxic speakers. Equivocal results were reported for relative timing and temporal stability. Conclusions: The results provide some preliminary evidence of reduced anticipatory lingual movement in AOS, and have demonstrated that this can have a significant impact on absolute speech timing. However, measures of relative timing were suggestive of either unimpaired or more extensive coarticulation. Additional research is required to resolve this issue