The Role of Selective Attention in Visual Working Memory Capacity: An ERP study

摘要

Visual working memory (VWM) capacity has been consistently measured both behaviorally and electrophysiologically using change detection tasks (See, e.g., Luck & Vogel, 1997; Vogel & Machizawa 2004). Many studies have estimated that the average healthy adult can hold 3a??4 items in VWM. Recent research suggests that selective attention influences storage capacity. Therefore, the present study sought to determine if sensory processing is enhanced at the locations of objects being encoded into VWM, just as in studies that directly manipulate spatial attention. Observers performed a lateralized change detection task, in which a cue indicates that subjects should encode the colors of the items on one side of fixation, ignoring the items on the other side. While subjects were encoding the items on one side, a high-contrast dartboard probe stimulus was sometimes presented on either the attended or unattended side. We examined neural activity during the maintenance interval when no probe was presented, along with the sensory response elicited by the probe stimulus. As in previous studies, the amplitude of the delay activity increased monotonically as the memory load increased, up to the storage capacity limit. We also found that the P1 sensory response elicited by the probe stimulus was enhanced when the probe appeared on the attended side of the display, indicating that encoding information into VWM involves a modulation of sensory transmission in the spatial region of the items being encoded. Moreover, the magnitude of this P1 sensory modulation was largest when the number of items being encoded was near the capacity limit (3a??4 items) and was much smaller when the number of items being encoded was either well below capacity (1a??2 items) or well above capacity (5a??6). These results suggest that visuospatial attention plays a role in VWM encoding, especially when capacity is being challenged.