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.
Coarticulation in recent speech production models
