A Psychophysiological Study on the role of working memory in a visual search

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We recorded the event-related potentials (ERPs) in the visual search, memory search, and mental rotation tasks, and observed a number of ERP changes, which reflected the processing of verbal, visual, and spatial information in a working memory. (1) The increase of visual items to be processed in a letter search task caused the increase of at lease two kinds of negativities, which can be differentiated by latency, topography, and sensitivity to how a target stimulus was designated. (2) In a delayed matching to sample task, the visual ERPs to the physically same stimulus differently influenced by memory load, depending on the kind of information (color, shape, or location) held in S1-S2 interval. (3) A concurrent mental arithmetic task selectively affected the amplitude and topography of the ERPs sensitive to memory load in the visual/memory search task. The ERP changes due to display load were not affected by this concurrent task. (4) Rehearsal of nonsense syllable performed concurrently with memory search task caused the decrease of N1 amplitude and the memory load effect of ERPs to auditory words, but did not affect ERPs to visual words or visual images. (5) The negative enhancement of ERPs due to stimulus angle in a mental rotation task was affected by a concurrent memory task for nonsense shapes, but not by memory for nonsense syllables. These suggest that the temporal and spatial patterns of ERPs can be indices of the operations of subsystems (verbal, visual, and spatial) in a working memory, and that the dual task approach is a useful method for disentangling the overlapping components, for inferring association between these electrophysiological measures and the processes involved in a working memory, and for estimating the roles and functional organization of multiple subsystems of working memory in various cognitive tasks.