Morphological errors and the representation of morphology in the lexical-semantic system.

Neuropsychological studies support the hypothesis that morphology is represented autonomously, both at the level of word meaning and at the level of word form. In output processes, morphologically organized semantic information activates lexical representations of roots and affixes, which are composed before production. In input processes, the stimulus is parsed along the morphological dimension, to access root and affix lexical representations, which in turn activate morphologically organized semantic information. Inflectional and derivational morphology are represented independently in the lexicon. Inflected words are fully decomposed; derived words are decomposed into base form + inflection. In aphasia, morphological errors in transcoding tasks always co-occur with semantic and/or phonemic errors. Morphological errors in transcoding tasks require combined damage to morphological representations in the semantic-lexical system and to sublexical conversion procedures; they co-occur with semantic errors when also root representations are damaged. The co-occurrence of morphological and phonemic errors can be accounted for by several hypotheses, but its theoretical meaning is still uncertain.