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Linda Moya, Sarah Shomstein, Anto Bagic, Marlene Behrmann; The time course of neural activity in object-based visual attention. Journal of Vision 2008;8(6):549. doi: 10.1167/8.6.549.
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Numerous studies provide evidence that attention can select objects in their entirety for preferential processing. A classic paradigm for eliciting object-based attentional effects, introduced by Egly et al. (1994), is to present two adjacent rectangles. Attention is cued to one end of one rectangle and then a target appears at the opposite end of the same, cued rectangle or at the parallel end of the adjacent un-cued rectangle. The general finding is that stimuli presented in the cued rectangle are responded to more quickly than stimuli presented in the adjacent rectangle even though both targets are physically equidistant from the cue. This faster reaction time is taken as evidence of object-based attentional processing. Shomstein and Behrmann (2006) adapted this paradigm in a functional magnetic resonance imaging (fMRI) study to locate the neural source of attention and found that the posterior parietal cortex (PPC) was differentially sensitive to the object-based properties of the input, with enhanced activation for locations bound by an attended object. They also found modulated activation in early cortical regions. Although the cortical regions associated with object-based attention are well-established, the temporal dynamics of these regions remains to be determined. The present research extends the paradigm using magnetoencephalography (MEG) to identify the temporal differences that exist between conditions in multiple cortical regions. Results indicate that differential MEG sensor activity and a sensor by condition interaction are found in parietal/occipital cortex. Furthermore, a sensor by condition by time interaction exists in frontal and occipital areas. The present findings provide temporal data that are compatible with the account that parietal/occipital areas modulate object-based attention, and therefore lay the ground work for further research into a comprehensive temporal and spatial understanding of the role of the frontal-parietal areas as the source of object-based attention and their modulation of more posterior areas.
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