15th International Congress of Phonetic Sciences (ICPhS-15)

Barcelona, Spain
August 3-9, 2003

Cerebellar Contributions to Speech Motor Control and Auditory Verbal Imagery: Acoustic/Kinematic Analyses of Ataxic Dysarthria and Functional Magnetic Resonance Imaging in Healthy Subjects

Hermann Ackermann, Ingo Hertrich

University of Tübingen, Germany

Acoustic analyses of sentence utterances noted slowed speech tempo, concomitant with a tendency towards syllable isochrony, in patients with impaired vocal tract control due to ataxic disorders. Furthermore, kinematic measurements revealed decreased maximum velocity of articulatory orofacial gestures with respect to a given movement amplitude. Syllable lengthening seems to develop into a plateau effect at a speaking rate of about 3 Hz both during sentence productions and oral diadochokinesis tasks. Most noteworthy, functional magnetic resonance imaging (fMRI) of cerebellar activation during syllable repetitions of varying frequencies in healthy subjects revealed a threshold effect of the calculated rate / response functions between 3 and 4 Hz. Recent psycholinguistic models of speech production assume a repository of overlearned syllable-sized articulatory routines housed within the premotor cortex (mental syllabary). Conceivably, the cerebellum participates in the retrieval of these syllable templates at a subject's habitual speaking rate (4 to 6 Hz) and contributes to their temporal organization in terms of a rhythmically structured utterance. Unexpectedly, a threshold effect of cerebellar activation even occurred during covert (silent) syllable productions (auditory verbal imagery). Presumably, thus, the cerebellum even contributes to the temporal organization of "internal speech", i.e., a prearticulatory, but fully parsed representation of the sound structure of sentences. As a consequence, cerebellar disorders may compromise any cognitive operations insofar as speech code-based information processing such as working memory rehearsal mechanisms or verbal thought associated with executive functions are involved.

Full Paper

Bibliographic reference.  Ackermann, Hermann / Hertrich, Ingo (2003): "Cerebellar contributions to speech motor control and auditory verbal imagery: acoustic/kinematic analyses of ataxic dysarthria and functional magnetic resonance imaging in healthy subjects", In ICPhS-15, 163-168.