Internal structure of phonetic representations: Non-linear analyses of error data from patients with apraxia of speech.
Final Report Abstract
Compared to earlier investigations of apraxia of speech this project was outstanding for the size of the examined patient sample (N=33). This sample size would not have been achieved without the exceptional readiness of many clinical partners all over Germany to collaborate by assigning us patients who met the strict requirements of this experiment. The comparatively large sample allowed us (and will still allow us in the future) to re-analyze, on a substantial database, the factors considered to influence accuracy in apraxic speakers, and to evaluate the extent to which the patterns of individual patients conform to group averages. Thus far, this approach was exemplified for the factors syllable number, syllable complexity, and intrasyllabic consonant position, but more analyses of this kind will follow. We found clear length, position and complexity effects, but it turned out that the way errors were counted and how they were normalized had a strong impact. A major new achievement of this study was that we discovered a strong and rather consistent influence of the metrical pattern of two-syllabic words on accuracy in apraxia of speech. A facilitating effect of the trochaic stress pattern - the default pattern in German - had already been conjectured in our earlier work and was substantiated here on sound empirical grounds. The result suggests that segmental and prosodic aspects of speech motor planning are intertwined, which fits well with our idea of a nonlinear structure of phonetic plans. This outcome also formed the basis of a new project in which we plan to examine the impact of metrical cues on the re-acquisition of words in apraxic speakers. We also replicated and extended our earlier finding that phonetic plans, as described by accuracy data from apraxic speakers, have a nonlinear architecture. Our modelling of the new data yielded a similar shape of the tree-structure model of phonetic plans as in our earlier approach. Moreover, we were able to predict our old data by the coefficients of the new model. The shape of our probabilistic model highlights important details of the phonetic planning process, such as the costs of synchronizing two gestures, of gesture clustering within a syllable constituent, of onset- vs. coda gestures, and of realizing metrical patterns. This work has meanwhile inspired the design of a functional imaging study (in collaboration with P. Kellmeyer, C. Weiller (Freiburg) and D. Saur, Leipzig), in which we identified the brain regions whose BOLD activation during overt speaking is correlated with the modelled costs of the words of the Hierarchical Word Lists. We also started to work on dissimilarity measures of phonetic plans, allowing us in the future to compare error-based measures of the phonetic architecture of words with measures from other domains.
Publications
- (2008). Editorial. Aphasiology, 22, 1123-1126
Ziegler, W. & Aichert, I.
- (2008). The domain of phonetic encoding in apraxia of speech: Which sub-lexical units count? Aphasiology, 22, 1230-1247
Ziegler, W., Thelen, A.-K., Staiger, A. & Liepold, M.
- (2009). Modeling the architecture of phonetic plans: Evidence from apraxia of speech. Language and Cognitive Processes, 24, 631-661
Ziegler, W.
- (2010). Apraxia of speech: What the de-construction of phonetic plans may tell us about the construction of articulate language. In: Maassen, B. & van Lieshout, P.H.H.M. (eds.). Speech Motor Control: New developments in basic and applied research (pp. 3 – 21). Oxford University Press. Oxford
Ziegler, W., Staiger, A. & Aichert, I.
- (2010). Syllable- and Rhythm-based Approaches in the Treatment of Apraxia of Speech. Perspectives on Neurophysiology and Neurogenic Speech and Language Disorders, 20(3), 59-66
Ziegler, W., Aichert, I., & Staiger, A.
- (2010). Therapie bei chronischer Sprechapraxie: Vorgehensweise am Beispiel eines Patienten mit reiner Sprechapraxie. Forum Logopädie, 3, 6-13
Aichert, I. & Ziegler, W.
- (2011). Apraxic failure and the hierarchical structure of speech motor plans: A non-linear probabilistic model. In: Kent RD, Lowit A (Eds.), Assessment of Motor Speech Disorders. Chapter 15, pp. 305 – 323. Plural Publishing Group
Ziegler, W.
- (2011). Why is ['ju:do] easier than [ju've:l]? Perceptual and acoustic analyses of word stress in patients with apraxia of speech. Stem-, Spraaken Taalpathologie, 17, 15
Aichert, I., Büchner, M., & Ziegler, W.
