Disturbances of Oral Word Production

Disturbances affecting the oral production of single words are extremely common in language-impaired patients. There are three basic disturbances affecting word production (other than semantic deficits). They follow the stages of word sound production: accessing the forms of words from concepts, planning the form of a word for articulation, and articulation.

A disturbance in activating word forms from concepts is manifest by an inability to produce a word from a semantic stimulus (a picture or a definition), coupled with intact processing at the semantic and phonological levels (determined by answering questions about pictures, picture categorization tests, and repetition). The form of a patient's errors is not a good guide to whether he or she has an impairment at this level of the production process since disturbances in accessing word forms may appear in a variety ofways, ranging from pauses to neologisms (complex sequences of sounds that do not form words) and semantic paraphasias (words related to the meaning of the target item). Rarely, patients show an inability to name objects presented in one modality only (e.g., visually) even though they demonstrate understanding of the concept associated with that object when it is presented in that modality (optic aphasia). Because disorders of basic sensory and motor functions can be ruled out in these patients, these modality-specific naming disorders have been taken to reflect a failure to transmit information from modality-specific semantic systems to the processor responsible for activating the forms of words.

Disturbances of a patient's ability to convert the representation of the sound of a word into a form appropriate for articulatory production are usually manifest as phonemic paraphasias (substitutions, omissions, and misorderings of phonemes). Three features of a patient's performance suggest a disturbance in word sound planning. First, some phonemic paraphasias are closely related to target words (e.g., "befenit" for "benefit"). Second, some patients make multiple attempts that come increasingly closer to the correct form of a word. Third, some patients make similar phonological errors in word repetition, word reading, and picture naming. Because the form of a word is presented to the output system in very different ways in these three tasks, the errors in such patients most likely arise in the process of planning the form of the word that is suitable for articulation.

Patients with sound planning problems tend to be more affected on longer words and on words with consonant clusters. The frequency of occurrence of a word in the language has a variable effect on the occurrence of these types of errors. Planning disturbances only rarely affect function words compared to nouns, verbs, and adjectives. Some patients have trouble planning the sounds of words only when words are inserted into sentences, making phonemic paraphasias in sentence production but not naming or repetition tasks. In these cases, the errors probably arise when words are inserted into syntactic structures.

Patients often have disturbances of articulation, as shown by abnormalities in the acoustic waveform produced by a patient and in the movement of the articulators in speech. Investigators have identified two major disturbances of articulation—dysarthria and apraxia of speech. Dysarthria is marked by hoarseness, excessive nasality, and imprecise articulation, and it has been said to not be significantly influenced by the type of linguistic material that the speaker produces or by the speech task. Apraxia of speech is marked by difficulty in initiating speech, searching for a pronunciation, better articulation for automatized speech (e.g., counting) than volitional speech, abnormal prosody, omissions of syllables in multisyllabic words, and simplification of consonant clusters (often by adding a short neutral vowel sound between consonants). Both dysarthria and apraxia of speech result in sounds that are perceived as distorted. Apraxia of speech often cooccurs with dysarthria or with the production of phonemic paraphasias, and the relations between these disorders and the empirical basis for distinguishing one from another are the subject of active research.

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