Sources of spatial and feature-based attention in the human brain.

Editor's Note: These short, critical reviews of recent papers in the Journal, written exclusively by graduate students or postdoctoral fellows, are intended to summarize the important findings of the paper and provide additional insight and commentary. For more information on the format and purpose of the Journal Club, please see Attention is a critical component of visual perception because it involves the allocation of limited processing resources depending on current task demands. Most research has focused on our ability to co-vertly attend to specific regions within the visual field (spatial attention), often ignoring our perhaps equally important ability to attend to specific visual features across the visual field (feature-based attention). The behavioral benefits of both spatial and feature-based attention are unmistakably clear during visual search, a task that we perform often in our daily lives. For example, when searching for an item in a room (e.g., a pencil), you may have prior knowledge of the item's spatial location (e.g., on top of the desk) and one or more of its visual features (e.g., yellow). Both types of information are typically used to guide the deployment of attention and speed the search process. Converging evidence from neuropsy-chological, electrophysiological, neuro-imaging, and neurostimulation studies points to a critical role of frontal and pa-rietal regions in the top-down deployment of spatial attention (Kastner and Ungerleider, 2000). Much less is known about brain regions underlying feature-based attention, although several studies suggest that it may recruit a frontoparietal network similar to that involved in spatial attention (Liu et al., 2003). This raises the interesting possibility that spatial and feature-based attention involve common brain areas in frontoparietal cortex. To address this question, one would have to directly compare neural mechanisms of spatial and feature-based attention within the same subjects and using comparable tasks. With an appropriate design, such a study might also be able to address to what extent spatial and feature-based information are independently represented within these top-down source regions. In a study published recently in The Journal of Neuroscience, Egner et al. (2008) took a novel and elegant approach to address these questions using functional magnetic resonance imaging (fMRI) in human subjects. Using a factorial design, spatial and feature-based information were independently manipulated in a parametric manner. On each trial, subjects were presented with a central cue followed by a search display consisting of a blue and red diamond presented on both the left and …