Disturbances of Processing Morphologically Complex Words

Disturbances affecting both the comprehension and the production of morphologically complex words have been described. With respect to recognition of morphologically complex words, researchers have observed that some patients who make derivational paralexic errors (e.g., "write" — "wrote," "fish" — "fishing," and "directing" — "direction") in the oral reading of complex words have particular difficulty with the recognition and analysis of written morphologically complex words compared to morphologically simple words. A patient with a disturbance affecting the auditory processing of words with inflectional but not derivational morphology has been described.

Disturbances affecting morphological processing also appear in single-word production tasks. In one study, patients had difficulties in producing plural, possessive, and third-person singular forms of non-words. The fact that this disorder arose with nonwords that the patients were given by the experimenters suggests that the impairment affected the ability to construct new morphological forms. Such disturbances can arise in patients who perform well on tasks that require recognition and comprehension of written morphologically complex words.

Disturbances affecting the production of morphologically complex words are most commonly seen in sentence production, where they are known as "agrammatism" and "paragrammatism." The most noticeable deficit in agrammatism is the widespread omission of function words and affixes and the better production of common nouns. This disparity is always seen in the spontaneous speech of patients termed agrammatic, and it often occurs in their repetition and writing as well. Patients in whom substitutions of these elements predominate, and whose speech is fluent, are called paragrammatic. Recent observations have emphasized the fact that these two patterns cooccur in many patients. They may result from a single underlying deficit that has different surface manifestations.

Agrammatism and paragrammatism vary considerably, with different sets of function words and bound morphemes being affected or spared in different cases. In some patients, there seems to be some systematicity to the pattern of errors. For instance,

English agrammatic patients frequently produce infinitives (e.g., "to walk'') and gerunds (e.g., "walking") because these are the basic forms in the verbal system. In other cases, substitutions are closely related to the correct target. Agrammatics' errors also tend to follow the tendencies seen in normal subjects with respect to errors that "strand" affixes (e.g., "I am going to school" — "I am schooling to go") and the "sonor-ance hierarchy'' that establishes syllabic forms as easier to produce than simple consonants. Agram-matics generally produce real words, which makes for different patterns of errors in different languages that differ with respect to whether or not they require inflections to appear on a word. The fact that in almost all cases errors do not violate the word-formation processes of the language suggests that most agram-matic and paragrammatic patients retain some knowledge of the rules of word formation.

Adult Dyslexia

Adult Dyslexia

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