Chapter 1 Apraxia of speech: what the deconstruction of phonetic plans tells us about the construction of articulate language Wolfram Ziegler, Anja Staiger, and Ingrid Aichert Abstract Apraxia of speech is considered as a speech motor planning impairment. Apraxic speech errors may therefore inform us about the structure of phonetic plans. Recent studies have suggested that syllabic motor integration mechanisms play a role in apraxic error generation, which contradicts earlier views of a segment-by-segment planning process. However, learning experiments in apraxic speakers have revealed that syllables should not be viewed as indivisible motor primitives. Moreover, supra-syllabic (metrical) mechanisms can also be shown to play an important role in the genesis of apraxic errors. We therefore propose a non-linear architecture of phonetic representations which embraces gestural, syllabic, and metrical tiers. 1.1 Introduction 1.1.1 Syllables and phonemes in phonetic encoding Speech is probably one of the most complex and most intensively exercised motor skills of humans. All normally developing individuals learn it from birth on and exercise speech motor behaviour day by day, over their whole lifetime. How can we describe the processes or representations that are constituted through speech motor learning? What are the core features of this highly automated skill that are established dur- ing its acquisition? The theory developed by Levelt and coworkers (Levelt et al., 1999) gives a clear answer to this question: It postulates that during speech motor learning we acquire motor pro- grammes for frequently occurring syllables and store them in a ‘mental syllabary’. Experimental evidence for the existence of a mental syllabary comes from reaction time data showing that, in naming tasks, the production of high-frequency syllables involves shorter laten- cies than the production of syllables with lower frequencies (Carreiras and Perea 2004; Cholin 2008; Cholin et al., 2005, 2006; Laganaro and Alario 2006; Levelt and Wheeldon 1994). Over and above such experimental evidence there is a further important reason why syllables might be 01-Maassen-Chap-01.indd 3 01-Maassen-Chap-01.indd 3 2/3/2010 12:09:50 PM 2/3/2010 12:09:50 PM