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CHAPTER 7
Chapter Overview
Ataxic dysarthria is caused by damage to the cerebellum or to the neural pathways that
connect the cerebellum to other parts of the central nervous system, resulting in speech
errors that are primarily articulatory and prosodic, giving speech an unsteady, slurred
quality. The cerebellum, which is located below the occipital lobe and attached to the
back of the brainstem, is a very important part of the motor system. Its primary function is
to coordinate the timing and force of muscular contraction so skilled, voluntary
The cerebellum influences speech movements through the corticocerebellar control
circuit and through its connections to the extrapyramidal system. The movement deficits
of timing, force, range, and direction are known as cerebellar ataxia. Ataxic dysarthria
can be caused by degenerative diseases, stroke, toxic and metabolic conditions,
traumatic head injury to the cerebellum, tumors, viral infections that invade the
cerebellum, and bacterial abscesses near the cerebellum. Tumors affect the cerebellum
by: growing in cerebellar tissue, directly destroying cells and compressing the cerebellum
if it grows large enough; growing near the cerebellum, compressing cerebellar tissue; or
a brainstem tumor may interfere with the functions of cerebellar control circuits. The
appearance of ataxic dysarthria depends on the location and size of the tumor.
Individuals with ataxic dysarthria give the impression that the movements of their speech
mechanism are poorly coordinated, due to problems controlling the timing and force of
many muscular contractions that are needed to produce clear articulations, resulting in a
drunken quality to their speech. Articulation is slurred and prosody is monotonous. Ataxic
dysarthria is primarily a disorder of articulation and prosody. Scanning speech is used to
Motor Speech Disorders, Second Edition
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Prosodic errors are also prominent in ataxic dysarthria and include equal and excess
stress, prolonged phonemes, prolonged intervals between phonemes, monopitch,
monoloudness, and slow rate. One of the hallmarks of cerebellar damage is slow
movement on both single and repetitive motion tasks. Monopitch and monoloudness are
caused by hypotonia of the speech muscles. Few phonatory deficits are noted in patients
with ataxic dysarthria. Harsh vocal quality is the most common, caused by decreased
muscle tone in the laryngeal and respiratory structures, preventing full contraction of
these muscle groups. Voice tremors may be noted. With regard to resonance,
hypernasality is seldom a serious problem, but intermittent hyponasality may be evident
One key evaluation task is speech alternate motion rates, which will most likely be slower
than normal. The patient will also be unable to maintain a steady rhythm when repeating
target sounds. The other key evaluation task is reading, conversational speech, and
repeating sentences containing numerous multisyllabic words. Inaccurate speech
movements, irregular articulatory breakdowns, and other prosodic errors in connected
speech will be revealed. Treatment for ataxic dysarthria involves treating speech errors
related to articulation and prosody. With regard to respiration, most patients do not need
to work on strengthening their respiration abilities, but rather should concentrate on
controlling their airflow more accurately during speech. Tasks include slow and controlled
exhalation, speaking immediately on exhalation, stopping phonation early, and using
optimal breath groups. Prosodic problems involve rate, stress, and intonation. Often by
reducing rate slightly, intelligibility improves. Use of more typical stress and intonation
into their utterances will help speech gain a more natural quality. While slow or irregular
speech is characteristic of ataxic dysarthria, many patients will attempt to speak at a rate
Motor Speech Disorders, Second Edition
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Study Questions and Answers
1. Define ataxic dysarthria in your own words.
prosodic errors that give individuals an unsteady, slurred quality of speech.
2. What is the primary function of the cerebellum?
3. Describe the neural pathways leading to and from the cerebellum.
4. What are the two ways that the cerebellum probably influences speech
production?
5. What is autosomal cerebellar ataxia of late onset?
6. Describe three ways in which a tumor can affect cerebellar function.
7. Which two components of speech production are usually affected most in
cases of ataxic dysarthria?
8. What is decomposition of movement?
9. Is hypernasality a significant problem in most cases of ataxic dysarthria?
10. Describe an exercise that can help individuals with ataxic dysarthria more
accurately control their airflow during speech production.
