Effects of morphological complexity on phonological output deficits in fluent and nonfluent aphasia

This study examined the effects of morphological complexity on aphasic speakers with lexical-phonological output deficits. Subjects were two fluent and two nonfluent aphasic speakers who repeated morphologically simple words at the same level of accuracy and whose errors were virtually all phonological in nature. They were asked to repeat a variety of morphologically complex (i.e., affixed) words. Results were interpreted within our two-stage model of lexical-phonological production (Kohn & Smith, 1994, 1995), which we expand to include a distinction between derivational and inflectional morphology. When comparing overall performance levels between morphologically simple and complex words, only three subjects exhibited more difficulty repeating the morphologically complex targets. Nevertheless, when comparing repetition accuracy between different types of morphologically complex words (e.g., derived vs. inflected), all four subjects displayed similar patterns. These findings suggested that while morphological complexity has different effects on the two stages within the lexical-phonological output system, the relative effects of different morphological structures are constant. At the level of error analysis, patterns of affix errors distinguished the nonfluent from the fluent subjects in ways that are reminiscent of the affix errors associated with agrammatic and paragrammatic speech. This finding raised questions concerning the relationship between morphosyntactic and morphophonological deficits.