Lexical and semantic binding effects in short-term memory: Evidence from semantic dementia

Two case studies are presented of the short-term memory performance of patients with semantic dementia. The first case showed a pervasive pattern of semantic effects in his auditory verbal short-term memory performance, in particular a marked superiority in serial recall for sequences of "known" words over "unknown" words-words which he no longer comprehended. His performance in serial recall tasks was characterised by abundant phonemic errors, which occurred with a frequency shown to be related to semantic factors. These errors were often migrations of phonemes from one word in the List to another, suggesting that impaired semantic processing reduces the "glue" or "binding" that helps to maintain a structured sequence of phonemes in short-term memory. The second patient also showed some semantic effects in serial recall: and a significant but less marked pattern of phonological errors. The differing performance of the two patients is interpreted within an interactive activation model of word production (Saffran & Martin, 1990; Martin, Saffran, & Dell, 1996).