Abstract
Concurrent working memory load can be increased without any effect on the neural processing of unattended scenes (Yi et al., 2004). However, different subsystems of working memory may use different processing resources, which may or may not interact with concurrent perceptual processing. To investigate this further, subjects performed foveal spatial or object n-back tasks while irrelevant scenes were presented in the peripheral background. The stimuli set consisted of nondescript shapes presented one at a time in different locations. Visuomotor stimulation was identical for all conditions; only attentional set differed. Load was manipulated by varying the number of items held in memory; behavioral performance on the low load tasks (spatial 1-back and object 1-back) was significantly better than on the high load tasks (spatial 3-back and object 2-back). To examine the effects of spatial and object working memory load on unattended scene processing, we compared event-related fMRI BOLD responses in the parahippocampal place area (PPA). PPA activation was significantly attenuated during spatial high load trials compared to spatial low load trials, supporting our hypothesis that perceptual processing involves an inherently spatial component. Interestingly, there was also an effect of object working memory load, suggesting that working memory for certain stimuli (i.e., shapes but not faces) may share processing resources with the task-irrelevant scenes (c.f., Kim et al., 2005). Thus, concurrent working memory load can interfere with visual processing of unattended scenes in the PPA, suggesting that task-related forms of working memory exert top-down influence on the attentional control of perceptual processing.
Supported by NIH grant EY014193.