Can phonological and semantic short-term memory be dissociated? Further evidence from landau-kleffner syndrome.

Recent studies have made a distinction between short-term storage capacities for phonological information and short-term storage capacities for lexico-semantic information (R. Martin, Lesch, & Bartha, 1999). In this multiple case study, we tried to provide further evidence for the dissociability of phonological and lexico-semantic short-term memory (STM) components, by studying verbal STM in three patients who had recovered from Landau-Kleffner syndrome. Furthermore, we explored to what extent apparent dissociations between phonological and lexico-semantic STM could be related to underlying phonological and lexico-semantic processing impairments. We found clear dissociations between phonological and lexico-semantic STM measures in patients TG, JPH, and DC, whose performance was impaired in nonword immediate serial recall and in a rhyme probe task, while performance was normal for a category probe task. These patients also presented reduced phonological effects (word length, phonological similarity, phonotactic frequency) but normal lexico-semantic effects (lexicality, word imageability, word frequency) in STM. Moreover, there were no systematic correspondencies between phonological and lexico-semantic STM and phonological and lexico-semantic processing impairments. Implications for current models of STM and language processing are discussed.