Abstract
The purpose of this study was to investigate working memory : phonological loop function in two patients with selective impairment of auditory-verbal span, using a dual-task paradigm.
Patient MO showed verbal short-term memory defects without other cognitive dysfunctions. Patient TU closely resembled patients with pure verbal short-term memory defects, except that he had minimal aphasia.
According to Baddeley's working memory model, verbal short-term memory relies basically upon a specialized “slave” system : the phonological loop. Vallar et al. indicated that selective impairment of verbal short-term memory is conceivably a capacity limitation of the phonological short-term store.
Our dual-task paradigm was measured by performance on visual checking or reading tasks and during concurrent digit span tasks. We compared performance to that of a group of age-matched controls. Performance measurements of the two patients were normal on tasks requiring central executive function. TU exhibited greater deficits than the control subjects when he was required to rehearse uttering of digits. In reading performance on dual-task conditions, MO needed longer reading time than the control subjects ; TU, however, was unable to continue this task.
These contrasting patterns of impairment suggest that a “specific” verbal short-term memory defect in TU may be associated with other defects in phonological processing.
