we get into apraxia of speech (AOS) you will need to review
your neuroanatomy notes on the upper motor and lower motor systems. The motor
system is present at all levels of the nervous system. It
includes "efferent connections of the cortex, especially the
frontal lobes; the basal ganglia, cerebellum, and related
CNS pathways; descending pathways to motor nuclei of cranial
and spinal nerves; efferent fibers within cranial and spinal
nerves, and striated muscle" (Duffy, 1995, p. 21). In
addition, you must remember that the planning/programming
associated with motor speech is thought by many to occur in
Broca's area on the third frontal convolution, although a
recent study has found that the Island of Reil was involved
in 25 stroke patients who had a disorder involving the motor
planning of speech (muscle movements) (Dronkers, 1996).
Apraxia of speech (AOS) is believed by most rersearchers to
result from a Broca's area lesion. According to Duffy
(1995), who is with the Mayo Clinic, AOS as the primary
speech pathology accounted for 9% of patients with motor
speech disorders seen at the clinic between 1987 and 1990.
In addition it is seen as a secondary diagnosis with
aphasias and other neurological disorders. Remember, it is
not a neuromuscular disorder. It is a planning/programming
problem. According to Duffy, 1995, vascular lesions are the
most prevalent cause of AOS. In addition he states that most
cerebral vascular accidents (cva's) occur in the
cerebral artery of the left hemisphere.
I like the
neurological model of communication developed by Meitus and
Weinberg, 1983, It enables one to clearly see the steps
involved in oral communication from the development of the
concept to the production of speech.
Weinberg (1983, p.227) have four ordered steps or levels in
their neurological model of oral communication. They are:
- Ideation - when the concepts we wish to
express are generated
- Symbolization - when these concepts
are put into a symbolic system congreunt with the rules
of the speaker's language;
- Translation - when these linguistic
units or symbols are translated into neuromotor commands
that result in the innervation of the motor
- Execution - the actual movements
of the speech mechanism.
Meitus & Weinberg (1983), impairments at each of these
levels will result in a different disorder:
- Impairment at
the ideation level will result in
mental- verbal dysfunction (or mental confusion,
dementia, confused language)
- Impairment at
the level of symbolization will result in
- Impairment at
the level of translation will result in
apraxia of speech
- Impairment at
the level of execution will result in
Halperin (1986 in Chapey, 1986, p.422), "apraxia of speech
is an articulation disorder that results from impairment due
to brain damage, of the capacity to order the positioning of
speech musculature and the sequencing of muscle movements
for volitional production of phonemes and sequences of
phonemes; but it is not accompanied by significant weakness,
slowness, or incoordination of these same muscles in reflex
and automatic acts." There is a great difference between
motor speech programming and the neuromuscular execution of
With an acquired
motor disorder of speech (as is dysarthria), basic language
processes are intact, (although some would consider apraxia
to be a type of phonoligical aphasia) but the mechanical
production of speech is impaired because of nervous system
Apraxia of speech
is a disruption of the capacity to program the skilled oral
movements necessary for speech. The problem is with the
programming associated with incorrect neural commands at
higher, more central levels.
from the Greek word "praxis," which means action.
In the past,
apraxia was often classified as a type of articulation
disorder and was in fact called central dysarthria by some.
Now, it is considered a motor planning/programming deficit.
According to Wertz (1984), apraxia of speech "is a
neurogenic phonological disorder, resulting from the
sensorimotor impairment of the capacity to select, program
and execute coordinated movements of the speech musculature
for the production of voluntary speech." In other words, the
part of the brain that generates the motor programs for
speech/phonology is damaged. Darley et.al. 1975 have
referred to the motor planning aspect of language/speech as
the motor speech programmer (MSP). Kearns and Simmons (1989,
in Northern, 1989) reported that research using
spectographic analysis of voice onset time (VOT) supports
the programming position. The following physiological
studies support the spectrographic results: fiberoptic
observation, electromyography, voicing measures, and
apraxia is another planning deficit that
impairs the voluntary movements of the arms, hands, legs and
feet. Many tests used to diagnose receptive aphasia require
patients to respond to questions by pointing at items or
following commands involving limb movement like "scratch
your nose." For this reason, speech pathologists must be
aware that a person's poor scores on some sections of an
aphasia battery may be due to limb apraxia rather than
aphasia. lesions that cause limb apraxia are usually in the
pre-motor area, Brodmann's area 6. According to
Duffy, 1995, limb apraxia is a disorder of the dominant
hemisphere, i.e. the left hemisphere for most..
As with apraxia of
speech, voluntary movements of the limbs are affected by
this disorder, but often involuntary movements remain
intact. A patient with this problem would be unable to
follow the command "scratch your nose" but could perform
this action with ease if his/her nose were itching.
apraxia is an inability to make voluntary,
non-speech oral movements. A person with this problem would
be unable to stick out his tongue if told to do so, but
could perform this action without struggle if given an
icecream bar to eat. As the auditory comprehension sections
of some aphasia batteries include commands involving oral
structures like "lick your lips," oral apraxia may also be
mistaken for aphasia.
refers to difficulty with programming the motor movements
involved in walking.
the swallow refers to a patients inability to
Darley (1978, as cited in Meitus & Weinberg, 1983, p.
266), the characteristics of apraxia of speech are as
patient struggles to avoid errors and to
correct articulatory positioning, leading to
alterations (slow rate, equalization of syllabic
errors predominate, but some prolongations,
additions, and repetitions occur. Distortions and omissions
are less frequent . Recent studies using instrumentation and
narrow transcription reveal that distortions are actually
the predominant error, but using broad transcription and
listening, substitutions errors seem most common (Wertz, et
al., 1984, p. 53).
Sound or syllable
transpositions may be present.
articulatory errors are complications rather than
Errors are often
approximations. There is variability in type of
articulatory errors, and instances of error-free fluent
speech on some words, phrases, and
occasionally on sentences.
errors may be present. The patient
anticipates a speech sound which will occur further on in
the word or sentence.
There is greatest
difficulty in initiating speech, as noted by hesitations,
and nonfluencies, visible searching, groping movements of
the articulators, numerous trials, and false starts (this
comprehension and word
recognition abilities are often
disproportionately better than speech production
recognize their articulatory
The number of
errors increases as a function of word length.
More errors occur
on consonants, and sounds which require
precise articulatory adjustments, e.g. fricatives and affricates. Consonant
clusters are most difficult of all.
Palatal and dental
phonemes are associated with a high rate of
errors (Halperin, 1986 in Chapey, 1986).
is noted during purposeful
speech than during the production of
reactive, automatic, or emotional speech.
increased errors in the production of words such as
nouns, verbs, adjectives and adverbs, which carry more
linguistic weight (Meitus & Weinberg, p. 268).
phonemes is higher (Wertz et al. p.
Accuracy is better
speech compared to nonsense stimuli (Wertz
et al. p. 63).
Fewer errors are
made during unstructured spontaneous
language than in word repetition or imitation
tasks (Chapey, 1981). However, there is debate about this,
with Wertz et al., 1984, (p. 66) believing the opposite to
Patients do better
with stimuli presented by a visible examiner
(auditory-visual mode) than with
stimuli presented on a tape recorder (Halperin,
Patients do better
given repeated trials of a word rather than with
increased stimulus presentations. In other words,
stimulus presentation with several opportunities to imitate
better than the converse. (Johns and Darley, 1970, in
Halperin, 1986) This has important implications for
benefit when using the following:
patients observe themselves in a mirror,
masking noise to prevent patients from
hearing their own speech,
delaying the patient's imitative
instructional set given to the patient as to the task's
metronome (Halperin, 1986).
Apraxia of speech
is often, but not always, accompanied by
motor apraxia, or an inability to volitionally
move the mouth, tongue, lips, cheeks, larynx, and pharynx as
directed (Halperin, 1986).
Some patients who
suffer from apraxia of speech have impaired oral sensation and
perception (Wertz et al., 1984 p. 75).
taken from Halperin (1984), who himself draws from numerous
sources, is somewhat redundant but it may help you better
understand apraxia of speech:
Involuntary speech is relatively
involves problems with motor planning for voluntary or
purposeful speech, involuntary speech or the recitation of
common, over-learned phrases and sayings remains remarkably
intact. A patient with apraxia may struggle and appear to
"grope" for sounds when trying to produce simple sentences
or even single words during a conversation but might be able
to recite the Lord's prayer or the Pledge of Allegiance
clearly and easily.
imitative responses are even more difficult to produce than
spontaneous speech, possibly because this kind of speech is
errors increase as the complexity of the motor adjustment
required of the articulators increases.
Therefore, it is
easier for the apraxic patient to produce vowels than
consonants. Single consonants are more readily produced than
blends or clusters. Fricatives and affricates are the
hardest manner of production for apraxics to master. As for
place of production, palatal and dental phonemes seem to be
the most difficult sounds. In general, phonemes that occur
with high frequency in the language reproduce more
accurately than those that occur less frequently.
errors will increase as the length of words increases. When
saying a multi-syllable word, an apraxic may produce the
syllables out of order.
Some errors are
stutterers, apraxics will sometimes realize that they are
going to have difficulty producing an up-coming sound and
hesitate. Such pauses make apraxic speech dysfluent and
Some errors are
patient will have difficulty virtually every time he/she
tries to produce certain sounds or certain words. According
to Deal (1974, as cited in Halpern, 1984), apraxic patients
demonstrate a "consistency" effect when asked to read the
same passage several times. That is, they make errors in the
same places during all trials.
apraxics will error repeatedly on the same word, the
specific off-target approximations produced will vary. For
example, if an apraxic patient has difficulty saying the
word "telephone" he/she may first err by saying "pelephone"
but then mispronounce the target as "kelephone" or
"felephone" on the next trial.
are misarticulated more frequently than are consonants in
is another way in which apraxic speech resembles stuttered
speech. Initial consonants may be more difficult for
apraxics because they are more affected by the anticipation
of errors. Also, it may be that once the apraxic has started
a word and produced a vowel sound, this helps them to ease
into the production of the remaining consonants.
errors occur more often on words that carry a lot of
psychological or linguistic weight and are therefore most
essential for communication.
is yet another way that apraxic speech resembles stuttered
Errors are often
off-target approximations of the desired articulatory
are more likely to differ from targets in terms of place and
manner of articulation rather than voicing.
omissions, distortions, additions and transpositions all
occur, substitutions are the type of error most frequently
made by apraxics.
According to Johns
and Darley (1970, as cited in Halpern, 1981), patients are
more likely to produce an articulatory target correctly when
they are given several opportunities to do so.
Repeated presentation of the target
by the clinician, on the other hand, is not helpful. This
means that the clinician should present a stimulus once and
then give the patient four or five chances to repeat
The modality in
which a stimulus is presented influences the articulatory
success of apraxic patients.
repititions of an individual with apraxia are more accurate
when they are able to watch a clinician produce the target
(speech reading the clinician) than when they only hear or
read the stimulus.
Finally, it should
be noted that there are several different types of apraxia.
The form of the disorder that affects speech should really
be called apraxia of speech or verbal apraxia to distinguish
it from these other types