Brain and Language 103 (2007) 8–249 www.elsevier.com/locate/b&l
Interpreting speech errors in aphasia Jean K. Gordon
*
Department of Speech Pathology & Audiology, University of Iowa, 125 B, WJSHC, 250 Hawkins Drive, IA 52242-1012, USA
Speech errors in aphasia have long been interpreted as a window onto the mechanisms of word retrieval. In modelling word retrieval, it is generally agreed that two successive stages are required: translating conceptual information into a lexical representation, and translating that lexical representation into a phonological word form. Each level of representation— conceptual, lexical, and phonological—and the processing stages between them, are candidates for potential breakdown, resulting in anomia. However, only the final product of this chain of events—the articulated response—is observable, making inferences about the underlying impairment difficult. It is often assumed that the predominant type of paraphasic error produced by an aphasic speaker transparently reflects the nature of that speaker’s underlying impairment (e.g. Gainotti, 1987; Kay & Ellis, 1987; Laine, Kujala, Niemi, & Uusipaikka, 1992; Lambon Ralph, Sage, & Roberts, 2000). Wilshire and Coslett (2000) propose that there exist two main types of anomia: semantic anomia, an inability to recover the complete semantic description of the concept, and output anomia, an impairment in retrieving the full phonological description of the target word. If anomia arises from breakdown at one of two separate stages—retrieval of semantics or phonology—then the majority of naming profiles should similarly break down into those with predominantly semantic or predominantly phonological errors. Mixed cases would be expected to occur, but relatively rarely and usually with more severe anomia. In group studies, this distribution has not been observed; rather, mixed patterns of errors appear to be the norm (e.g. Ardila & Rosselli, 1993; Butterworth, Howard, & McLoughlin, 1984; Goodglass, Wingfield, & Hyde, 1998; Laine et al., 1992). Such observations have called into question the assumption that errors transparently reflect the underlying deficit. An alternative hypothesis is that anomia is a unidimensional impairment in the ability to retrieve word forms from activated semantics. Variations in error pattern can be attributed to factors other than the locus of the underlying deficit, such as: severity of anomia; stimulus characteristics (e.g. frequency, length, grammatical category, number of competitors); and differences in task demands that may foster strategic responses. These hypotheses can be explored by examining the distributions of word-retrieval errors produced by subjects with aphasia. The current study involves a retrospective analysis of picture naming errors by subjects with aphasia, with the aim of providing preliminary evidence to motivate a large-scale prospective study of the mechanisms underlying different types of word retrieval error. *
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doi:10.1016/j.bandl.2007.07.075
Methods Thirty-two subjects with aphasia, representing a range of aphasia subtypes and severity levels, participated in the study. They named 175 line drawings of objects from the Philadelphia Naming Test (PNT, Roach, Schwartz, Martin, Grewal, & Brecher, 1996). Paraphasic responses were classified by their relationship to the target—semantic, phonological, mixed, or unrelated. Non-naming responses included circumlocutions and non-responses. The incidence of semantic and phonological errors was examined across subjects for evidence of bimodality in the distributions, which would support the hypothesis that such errors reflect breakdown in the retrieval of either semantic or phonological information, respectively. Relationships among the error types were examined using correlational analyses. If subjects have a tendency to make predominantly semantic or phonological errors, these error rates should be negatively correlated. Results Fig. 1 shows the distributions of error responses across subjects. The distribution of semantic errors is unimodal, peaking at 6%, with one outlier, indicating that the occurrence of semantic errors is unlikely to reflect the presence or absence of an underlying semantic impairment. The distribution of phonological errors, on the other hand, is bimodal, with one peak at 2% and another at 16%, suggesting that most aphasic speakers produce a few phonological paraphasias, but some produce an abundance of them. Correlations among the error rates indicated that all error types were significantly correlated (p < 0.05, Bonnferroni corrected) with the overall severity of the naming impairment (r > 0.52), with semantic errors showing the strongest relationship (r = 0.684). Semantic error rates were significantly correlated with mixed errors and circumlocutions but, critically, not with phonological error rates (r = 0.116). No other inter-correlations were significant. Conclusions Results support the hypothesis that a high incidence of phonological paraphasias is indicative of an underlying impairment in phonological encoding. However, the distribution of semantic errors suggests that these errors are influenced by factors other than a hypothesized deficit at the level of semantic retrieval. One of these is the severity of the naming impairment, but further investigation is needed to determine what other factors contribute. Analyses of characteristics of the stimuli and the sub-
Abstract / Brain and Language 103 (2007) 8–249
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Error Distributions 20
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Fig. 1. Numbers of subjects demonstrating different types of errors.
jects’ performance on other language tasks are ongoing. This conclusion supports previous work cautioning against a straightforward interpretation of underlying deficit from semantic errors (e.g. Caramazza & Hillis, 1990), and provides evidence from a larger group of subjects with aphasia. References Ardila, A., & Rosselli, M. (1993). Language deviations in aphasia: A frequency analysis. Brain and Language, 44, 165–180. Butterworth, B., Howard, D., & McLoughlin, P. (1984). The semantic deficit in aphasia: The relationship between semantic errors in auditory comprehension and picture naming. Neuropsychologia, 22(4), 409–426. Caramazza, A., & Hillis, A. E. (1990). Where do semantic errors come from? Cortex, 26, 95–122. Gainotti, G. (1987). The status of the semantic-lexical structures in anomia. Aphasiology, 1(6), 449–461.
Goodglass, H., Wingfield, A., & Hyde, M. R. (1998). The Boston corpus of aphasic naming errors. Brain and Language, 64(1), 1–27. Kay, J., & Ellis, A. W. (1987). A cognitive neuropsychological case study of anomia: Implications for psychological models of word retrieval. Brain, 110, 613–629. Laine, M., Kujala, P., Niemi, J., & Uusipaikka, E. (1992). On the nature of naming difficulties in aphasia. Cortex, 28, 537–554. Lambon Ralph, M. A., Sage, K., & Roberts, J. (2000). Classical anomia: A neuropsychological perspective on speech production. Neuropsychologia, 38, 186–202. Roach, A., Schwartz, M. F., Martin, N., Grewal, R. S., & Brecher, A. (1996). The Philadelphia Naming Test: Scoring and rationale. Clinical Aphasiology, 24, 121–133. Wilshire, C. E., & Coslett, H. B. (2000). Disorders of word retrieval in aphasia: Theories and potential applications. In Nadeau, Gonzalez Rothi, & Crosson (Eds.), Aphasia and language: Theory to practice. New York, NY: The Guilford Press.
