The present study proposes a new interpretation of the underlying distortion in APRAXIA OF SPEECH. Apraxia of speech, in its pure form, is the only neurolinguistic syndrome for which it can be argued that phonological structure is selectively distorted.

Apraxia of speech is a nosological entity in its own right which co-occurs with aphasia only occasionally. This…conviction rests on detailed descriptions of patients who have a severe and lasting disorder of speech production in the absence of any significant impairment of speech comprehension, reading or writing as well as of any significant paralysis or weakness of the speech musculature.

(Lebrun 1990: 380)

Based on the experimental investigation of poorly coarticulated speech of patients from two divergent languages (German and Xhosa) it is argued that apraxia of speech has to be seen as a defective implementation of phonological representations at the phonology–phonetics interface. We contend that phonological structure exhibits neither a homogeneously auditory pattern nor a motor pattern, but a complex encoding of sequences of speech sounds. Specifically, it is maintained that speech is encoded in the brain as a sequence of distinctive feature configurations. These configurations are specified with differing degrees of detail depending on the role the speech segments they underlie play in the phonological structure of a language. The transfer between phonological and phonetic representation encodes speech sounds as a sequence of vocal tract configurations. Like the distinctive feature representation, these configurations may be more or less specified. We argue that the severe and lasting disorders in speech production observed in apraxia of speech are caused by the distortion of this transfer between phonological and phonetic representation. The characteristic production deficits of apraxic patients are explained in terms of overspecification of phonetic representations.