Abstract Word Deficits in Aphasia: Evidence From Semantic Priming

Word Deficits in Aphasia: Evidence From Semantic Priming L. K. Tyler, H. E. Moss, and F. Jennings Birkbeck College, University of London J.G. and D.E. are nonfluent aphasic patients who appear to have selective problems with abstract words on a variety of standard tests. Such a pattern would normally be interpreted as indicating a central semantic deficit for abstract words. The authors show that this is not the case by means of a semantic priming task, which tests for implicit knowledge of the meanings of abstract and concrete words. Spoken word pairs that were either abstract or concrete synonyms (e.g., street-road or luck-chance) were presented, and it was found that both patients showed priming for the abstract and concrete pairs. The researchers followed up by asking the patients to produce definitions to spoken abstract and concrete words; these definitions were also normal. The priming and definition data suggest that the semantic representations of abstract words in these patients were relatively unimpaired. The researchers found that the patients have problems only with spoken abstract words in just those tasks where normal controls also have difficulty. In contrast, they clearly have deficits in reading abstract words aloud, which may be due to problems with output phonology. The implications of these data for claims concerning hemispheric differences in the representation of abstract and concrete words are discussed. There is considerable evidence from research with normal participants of a difference between abstract words—words such as truth, courage, usual, which refer to entities and events that cannot be experienced through the senses—and concrete words. Participants consistently perform better on concrete than on abstract words (e.g., Schwanenflugel, 1992); for example, lexical decision latencies are slower to abstract than concrete words, even when they are matched for familiarity and frequency (e.g., deGroot, 1989), and participants are slower to name an abstract than concrete word (e.g., Bleasdale, 1987).' Theoretical accounts of this pattern range from the dual coding hypothesis (Pavio, 1986), which emphasises the qualitative differences between abstract and concrete words, to the claim that the representations differ in amount rather than type of semantic information (Plaut & Shallice, 1993). Supporting evidence for the distinction between abstract and concrete words comes from the study of brain-damaged patients, where it has frequently been observed that many patients with acquired disorders of language have particular problems with abstract words (e.g., Franklin, 1989; Shallice & Warrington, 1975). Patients have been reported who have more difficulty with abstract than concrete words in reading tasks (Coltheart, Patterson, & Marshall, 1980), in repeating words (Franklin, Howard, & Patterson, 1994; Howard & L. K. Tyler, H. E. Moss, and F. Jennings, Centre for Speech and Language, Department of Psychology, Birkbeck College, University of London, London, England. This research was supported by a Medical Research Council program grant and a British Academy Fellowship award. Correspondence concerning this article should be addressed to L. K. Tyler, Department of Psychology, Birkbeck College, University of London, Malet Street, London WC1 7HX England. Electronic mail may be sent to [email protected]. Franklin, 1988), and in various comprehension tasks (Franklin, 1989; Franklin, Howard, & Patterson, 1994). When dissociations of this type are encountered—where performance on one type of word (e.g., concrete words) is relatively better than on another type of word (e.g., abstract words) and where this pattern holds across different input and output modalities—it is assumed that this reflects an impairment in the representation (rather than the access) of abstract words. On this kind of view, a selective impairment of abstract words arises because their underlying representation differs from that of concrete words. In other words, abstract and concrete words are qualitatively different from each other; they constitute different categories. Thus, the abstract word impairment is similar to a category-specific impairment where one specific category of knowledge is selectively impaired following brain damage. In this article, we explore the nature of the abstract word deficit in 2 aphasic patients—J.G. and D.E.—who on tests that are standardly used to assess the comprehension of abstract words score very poorly. They both have considerable difficulty reading abstract words compared with concrete words, and their auditory comprehension of abstract words, as measured by a word-picture matching task, is also impaired. When a patient shows impaired performance on abstract words in both the auditory and visual modalities, it is usually interpreted in terms of a central semantic deficit for abstract words rather than a modality-specific access impairment. The question we address in this article is whether this is indeed the case. Do J.G. and D.E. have a deficit in the semantic representation of abstract words even though the representation of concrete words remains unimpaired? 1 Schwanenflugel (1992) discussed some of the findings that complicate this general picture. 2 In this article, we have not distinguished between abstractness and low imageability. They were highly correlated, but our data did not allow us to distinguish between them.