A double dissociation between memory span and word processing among neurological patients attests to the functional independence of verbal short-term memory.

Abstract

Reports of patients with impaired verbal short-term memory are central to the debate of whether there are independent short-term stores or whether immediate repetition is supported by activated long-term memory. Patients with selective impairments of verbal short-term memory support models with independent buffers. However, it has been argued that these patients were too rare to provide reliable data. Second, it has been suggested that these patients might suffer from subtle impairments of word perception, comprehension or production which previous studies had failed to notice. Ten neurological patients were assessed. Nine participants had impaired immediate spans for digits, letters and words whilst having unimpaired word perception, comprehension and production. Another patient exhibited better preserved immediate repetition despite severely impaired word perception, comprehension and production. This double dissociation provides unequivocal evidence for the functional independence of short- and long-term memory. The size of the present group of STM participants, the largest to date, makes it impossible to ignore data from neuropsychological patients.