Apraxia of Speech

Characteristics

Apraxia of speech (AOS) is a neurogenic communication disorder affecting the motor programming system for speech production. Individuals with AOS demonstrate difficulty in speech production, specifically with sequencing and forming sounds. The Levelt model describes the speech production process in the following three consecutive stages: conceptualization, formulation, and articulation. According to the Levelt model, apraxia of speech would fall into the articulation region. The individual does not suffer from a language deficiency, but has difficulty in the production of language in an audible manner. Notably, this difficulty is limited to vocal speech, and does not affect signed language production. The individual knows exactly what they want to say, but there is a disruption in the part of the brain that sends the signal to the muscle for the specific movement. Individuals with acquired AOS demonstrate hallmark characteristics of articulation and prosody (rhythm, stress or intonation) errors. Coexisting characteristics may include groping and effortful speech production with self-correction, difficulty initiating speech, abnormal stress, intonation and rhythm errors, and inconsistency with articulation.

Wertz et al., (1984) describe the following five speech characteristics that an individual with apraxia of speech may exhibit:

Effortful trial and error with groping

Groping is when the mouth searches for the position needed to create a sound. When this trial and error process occurs, sounds may be held out longer, repeated or silently voiced. In some cases, an AOS sufferer may be able to produce certain sounds on their own, easily and unconsciously, but when prompted by another to produce the same sound the patient may grope with their lips, using volitional control (conscious awareness of the attempted speech movements), while struggling to produce the sound.

Self correction of errors

Patients are aware of their speech errors and can attempt to correct themselves. This can involve distorted consonants, vowels, and sound substitutions. People with AOS often have a much greater understanding of speech than they are able to express. This receptive ability allows them to attempt self correction.

Abnormal rhythm, stress and intonation

Sufferers of AOS present with prosodic errors which include irregular pitch, rate, and rhythm. This impaired prosody causes their speech to be: too slow or too fast and highly segmented (many pauses). An AOS speaker also stresses syllables incorrectly and in a monotone. As a result, the speech is often described as ‘robotic’. When words are produced in a monotone with equal syllabic stress, a word such as ‘tectonic’ may sound like ‘tec-ton-ic’ as opposed to ‘tec-TON-ic’. These patterns occur even though the speakers are aware of the prosodic patterns that should be used.

Inconsistent articulation errors on repeated speech productions of the same utterance

When producing the same utterance in different instances, a person with AOS may have difficulty using and maintaining the same articulation that was previously used for that utterance. On some days, people with AOS may have more errors, or seem to “lose” the ability to produce certain sounds for an amount of time. Articulation also becomes more difficult when a word or phrase requires an articulation adjustment, in which the lips and tongue must move in order to shift between sounds. For example, the word “baby” needs less mouth adjustment than the word “dog” requires, since producing “dog” requires two tongue/lips movements to articulate.

Difficulty initiating utterances

Producing utterances becomes a difficult task in patients with AOS, which result in various speech errors. The errors in completing a speech movement gesture may increase as the length of the utterance increases. Since multisyllabic words are difficult, those with AOS use simple syllables and a limited range of consonants and vowels.

Norma