Levels of morphological deficit: indications from inflectional regularity.

A language impairment that affects the production of inflected and/or derived words may result from a deficit that specifically affects morphological processing mechanisms, but it might also arise from whole-word processing failures as well (Badecker & Caramazza, 1987; Funnell, 1987). However, to motivate a true morphological impairment, the deficit must be understood in terms of one or more different levels of morphological structure. Minimally, we can distinguish a word's morphosyntactic representation from its morphophonological representation. In the single-case study reported here a deficit affecting the representation or processing of morphosyntactic representations is motivated. A critical part of the argument is that the deficit affects both regular and irregular inflection, and that no whole-word processing deficit can account for the particular pattern observed in this patient.