A FREQUENT OCCURRENCE - FACTORS AFFECTING THE PRODUCTION OF SEMANTIC ERRORS IN APHASIC NAMING

Both normal and aphasic subjects produce picture naming errors that ar e semantically related to the target. This study investigates the effe cts of different word properties on the production of semantic errors by aphasic subjects. A correlation is found between the production of semantic errors and deficits in the comprehension of high-imageability words, with those patients who make semantic errors in comprehension also producing them in naming. This suggests an absence of deficits re sulting in semantic errors only in word production. For some patients, semantic errors are more likely to occur with lower-imageability targ ets, despite the restricted range of imageability values for stimuli i n this picture naming task. However, not all of those patients who pro duce semantic errors show an effect of imageability on their occurrenc e, suggesting a dissociation between central conceptual/semantic defic its and post-semantic deficits. The majority of patients fail to show frequency effects in the production of semantic errors, contrary to th e predictions of most models of spoken word production. However, for s ome of those patients who have a central semantic deficit, there is an interaction between frequency and imageability, with a frequency effe ct for low-imageability items alone. It is argued that this is the mor e appropriate analysis rather than the study of main effects. The prob lems that the diverse patterns of presence and absence of frequency ef fects cause for current theoretical models of spoken word production a re discussed.