The differential effects of Sternberg short- and long-term memory scanning on the late Nd and P300 in a dual-task paradigm.

We previously reported that the late negative difference (Nd) waveform elicited during dichotic listening was reduced in amplitude by a concurrent simulated flying task having a wide variety of cognitive demands (Psychophysiology, 39, 2002, 236). The main purpose of the present study was to determine how tasks involving the specific demands of short-term memory (STM) or long-term memory (LTM) would influence the early and late Nd waveforms. To this end, 16 participants performed dichotic listening alone and in conjunction with the varied-set (STM) and fixed-set (LTM) versions of Sternberg's memory scanning paradigm. Event-related brain potential (ERP) data was collected concurrently from both the auditory and visual tasks. The results showed that the STM task, but not the LTM task, reduced the amplitude of the auditory late Nd. The auditory early Nd component was unaffected by either task. Furthermore, both the auditory and visual P300s were decreased in amplitude by all the dual-task conditions. These data suggest that the auditory late Nd is linked to more specific working memory processes than is P300.