Aphasia

Aphasia is a language disorder acquired subsequent to brain damage that affects production and understanding of spoken and written language in varying degrees and patterns associated with the size and site of the lesion (see Symptoms and Neurological Correlates). Written and online examples of aphasic speech are available (see Aphasic Language Data Sets). Brain damage is usually in the left cerebral cortex, with the left temporal and frontal lobes being especially vulnerable (see Symptoms and Neurological Correlates). Profiles of deficits vary in the extent that levels of language, phonology (see Phonemic and Phonetic Characteristics), lexis (see Nouns, Verbs, Closed-Class Words), and syntax (see Sentence Comprehension and Sentence Production) are involved, in varying degrees and patterns, although lexical access problems are found in most types of aphasia. These deficits give rise to problems in connected speech and conversation (see Discourse). Variations in the types of language deficit found in aphasia led to the notion of syndromes and the search for associations between types of language deficits and sites of lesion (see Historical Overviews). Two well-described syndromes are Broca’s and Wernicke’s aphasia. Broca’s aphasia is characterized by syntactic deficits in output but with relatively retained understanding of language. Most experimental research has been in this type of aphasia. In Wernicke’s aphasia, understanding is impaired and lexical semantics are compromised, whereas syntax is relatively intact. Aphasia is found in all languages (see Across Languages) and in children who have passed the early stages of language development and subsequently have impaired language following brain damage.