Apraxia of speech (AOS) is a neurogenic speech disorder that is characterised by deficits in the articulatory and prosodic domains of speech production. A range of physiologic assessment techniques have been employed in an attempt to elucidate the physiological underpinnings of articulatory and prosodic defects in AOS. However, despite the advancement of electromagnetic articulography (EMA), a technique that facilitates safe, non-invasive assessment of intra-oral structures, little research has investigated lingual kinematics during speech production in participants with AOS. Tongue-to-palate contact patterns, on the contrary, have been investigated in AOS. However, most of this research relied upon descriptive analysis, rather than instrumental techniques including electropalatography (EPG). Therefore, the present thesis aimed to utilise EMA and EPG to provide a comprehensive assessment of lingual movement and tongue-to-palate contact patterns during word-initial consonant singletons and consonant clusters, during mono- and multisyllabic words, in AOS. The strength of coupling between the tongue and jaw and tongue-tip and tongue-back was also examined, as was consonant cluster coarticulation. Five participants (three females and two males) with AOS and a concomitant non-fluent aphasia participated in the project. The mean age of the group at the time of the EMA assessment was 53.6 years (SD = 12.60; range 35 - 67 years). At the time of initial assessment, all participants were a minimum of 12 months post onset of stroke (M = 1.67 years; SD = 0.72). Perceptual analysis indicated that each of the five participants with AOS presented with the following mandatory characteristics: sound distortions, sound prolongations, syllabic speech output, and dysprosody. A control group of 12 neurologically unimpaired participants (8 male, 4 female; M = 52.08 years; SD = 12.52; age range = 29 - 70 years) also participated in the study. The apraxic speakers’ tongue-tip and tongue-back movements were initially profiled during monosyllabic word production using EMA. Movement duration, distance, maximum velocity, maximum acceleration and deceleration, and velocity profile index values were recorded during word-initial consonant singletons (i.e., /t, s, l, k/) and consonant clusters (i.e., /kl, sk/). Results indicated that the participants with AOS evidenced significantly prolonged movement durations and, in some instances, significantly greater articulatory distances, relative to the control group. All measures pertaining to speed appeared to be relatively unimpaired. Phonetic complexity had a variable impact on the articulation of word-initial consonants. The results were able to account for the overall slow rate of speech exhibited by the participants with AOS. In a subsequent study, EMA was employed to investigate the impact of increasing word length on lingual kinematics for five participants with AOS. Target consonant singletons and consonant clusters were embedded in the word-initial position of one, two, and three syllable words (e.g., tar, target, targeting). Movement duration appeared to be most sensitive to the effect of word length during consonant singleton production. However, word length effects were absent during consonant cluster production. The data were discussed in the context of motor theories of speech production. The final EMA investigation examined the strength of coupling between the tongue and jaw and tongue-tip and tongue-back during /ta, sa, la, ka/ syllable repetitions, in a group of five participants with AOS. In comparison to the control group, four participants with AOS exhibited significantly stronger articulatory coupling for alveolar and/or velar targets, indicative of decreased functional movement independence. The reduction in functional movement independence was thought to reflect an attempt to simplify articulatory control, or alternatively, a decrease in the ability to differentially control distinct articulatory regions. To complement the EMA data, EPG was employed to investigate the spatial characteristics of linguopalatal contact during word-initial consonant singletons (i.e., /t, s, l, k/) and consonant clusters (i.e., /kl, sk/) in three participants with AOS. Through the use of quantitative and qualitative analysis techniques, misdirected articulatory gestures (e.g., double articulation patterns), distorted linguopalatal contact patterns (alveolar fricatives), lingual overshoot, and for one participant, significantly greater spatial variability were identified in the linguopalatal contact data. Pattern of closure appeared to be relatively unimpaired during alveolar plosive and approximant productions, and lingual undershoot and true omission errors were absent. The results were discussed in relation to their impact on phonetic distortion. A subsequent EPG study examined the temporal and spatial aspects of consonant cluster coarticulation in three participants with AOS. Target stimuli included ‘scar’ and ‘class’. In contrast to what was expected, each of the participants with AOS appeared able to coproduce elements within a consonant cluster. Appropriately, pattern of linguopalatal contact did not appear to be influenced by coproduction. Amount of linguopalatal contact did differ significantly on occasion. Coarticulatory effects were appropriately absent for each of the participants with AOS during alveolar fricative production in ‘scar’; however, the control group and each of the apraxic speakers exhibited place of articulation assimilation during velar stop production. The control group and two participants with AOS produced discrete velar and alveolar articulations during ‘class’; one participant with AOS evidenced coarticulatory effects during the /kl/ cluster. The research findings indicated that consonant cluster coarticulation was generally maintained in word-onset position, and it was postulated that future research should endeavour to investigate consonant cluster coarticulation in consonant sequences that span a syllable boundary. The EMA and EPG research findings presented in this thesis inform about the underlying physiological nature of articulatory disturbances in AOS. These findings will be discussed in the context of contemporary theories of speech motor control.
| Identifer | oai:union.ndltd.org:ADTP/253937 |
| Creators | Meyer, Carly |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
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