Preserved morphological processing in semantic dementia

Individuals with semantic dementia (SD) show progressive worsening of lexical-conceptual single word knowledge alongside preservation of nonsemantic aspects of language. The current study examines morphological processing in SD. S.H.S., a Hebrew-speaking person with SD, completed eight tasks that tested inflection, linear derivation, and nonlinear derivation at three time points over six and a half years. S.H.S. correctly produced plural nouns and judged the grammaticality of noun-verb and noun-adjective inflectional agreement. A steeper decline was seen in the ability to judge irregularly versus regularly inflected forms. S.H.S. judged nationality suffixes accurately and produced diminutive and agentive suffixes successfully. He also relied on morphological decomposition when performing lexical decision. Judgement of sentences consisting of derived verbal participles was intact with regard to morphological considerations alone, but impaired when semantic considerations determined grammaticality. S.H.S.'s performance suggests that structural aspects of word knowledge might be functional in the face of a severe semantic impairment.