The analysis of morphological errors in a case of acquired dyslexia

An issue that is persistently raised in studies of subjects who produce morphological errors in reading and other tasks is whether these errors are the consequence of a morphological processing deficit, or whether they in any way reflect morphological principles of organization in the lexicon. We discuss the performance of one such subject on a number of tasks and evaluate standard arguments for attributing aspects of his performance to a morphological processing deficit. Although there are several features of his performance that are suggestive in this regard; we argue that, when these issues are addressed in the context of a sufficiently elaborated theory of lexical processing, a morphological processing deficit cannot be demonstrated. We also survey a number of recent reports that purport to provide evidence for a morphological processing deficit and argue that, in most cases, they fail to support such claims for similar reasons. An important moral to be drawn from a critique of these studies is that in order to make valid inferences concerning the role of morphology in organizing the lexicon, we must consider these errors in the context of theories of the lexicon that take seriously the effects of converging lexical factors in processing.