Modelling the architecture of phonetic plans: Evidence from apraxia of speech

Abstract

In theories of spoken language production, the gestural code prescribing the movements of the speech organs is usually viewed as a linear string of holistic, encapsulated, hard-wired, phonetic plans, e.g., of the size of phonemes or syllables. Interactions between phonetic units on the surface of overt speech are commonly attributed to either the phonological encoding stage or the peripheral mechanisms of the speech apparatus. Apraxia of speech is a neurogenic disorder which is considered to interfere with the mechanisms of phonetic encoding. Analyses of apraxic speech errors have suggested that phonetic representations have a non-linear, hierarchically nested structure. This article presents a non-linear probabilistic model of the phonetic code, which embraces units from a sub-segmental level up to the level of metrical feet. The model is verified on the basis of accuracy data from a large sample of apraxic speakers.

Keywords:

• Apraxia of speech
• Non-linear phonology
• Phonetic planning
• Speech production

Acknowledgements

This research was supported by DFG-grants Zi 469/4–1, 4–2, 6–1, 6–2, 8–1, 10–2. The speech therapy team from our clinical department is acknowledged for long-lasting and friendly collaboration. Michaela Liepold, Bettina Brendel, and Marco Mebus have contributed to many of the auditory analyses reported here. Some of the patients in this sample have thoroughly and extensively been examined by Ingrid Aichert and Anja Staiger, to both of whom I am also indebted for many fruitful discussions of the issues covered here. The final version of this article profited from the insightful comments of two anonymous reviewers and of Matthew Goldrick. I would also like to express my thanks to all the patients whose speech data ended up in the large database presented in this article.

Notes

¹As a matter of fact, violations of the final obstruent devoicing rule have, to my knowledge, not been reported in German apraxic speakers.