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Abstract:
The assumption that at least part of our movements, and in
particular the fast ones, are programmed before their initiation
is a well accepted concept in the research area of motor control.
Especially the successive rapid movements of speech are supposed
to be prepared and programmed before their initiation. Unilateral
lesions of the left hemisphere can produce speech motor disorders
described as apraxia of speech (AOS). AOS is often characterized
as a motor speech disorder in which the mechanisms of planning
and programming are disturbed. However, there is not much
empirical evidence for the interpretation of speech apraxic
symptoms in the sense of a programming deficit. A common
experimental approach to study motor programming has been the
reaction time paradigm. Increased reaction time in longer or more
complex movements have been taken as evidence that movements are
prepared or programmed in advance. We investigated 20 aphasic
patients with lesions of the left hemisphere. Ten of them had
apraxia of speech. 20 normal subjects served as controls. In a
simple reaction time experiment subjects were required to produce
stimuli of varying length and articulatory complexity as fast as
possible after an imperative signal. Reaction times (RT),
inter-syllable intervals (ISI) and speech errors (SE) were
analysed. Normal subjects and patients without AOS showed
increased RT with increasing utterance length. In contrast,
patients with AOS had increased RT and increased ISI in
utterances requiring higher articulatory demands. At the same
time they did not trade-off speed against articulatory accuracy.
It is concluded that patients with AOS have a specific deficit in
the programming of multiple gesture utterances, but not with
utterance length.
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