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Timothy J. Vickery, Yuhong Jiang; Perceptual set switching: How are target templates changed in visual tasks?. Journal of Vision 2004;4(8):688. doi: 10.1167/4.8.688.
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In real-world examples of visual search, our search is often not complete once a single item has been found. For instance, picking bits of change out of a handful requires reconfiguring the target template to each of the denominations needed to sum to a specific value. What are the characteristics of this reconfiguration, and does it share properties and/or rely on the same brain regions as other types of cognitive switching abilities? In behavioral and imaging studies, we investigated the characteristics of perceptual set switching. The color of a target was sometimes altered from trial to trial by changing the cue color, while the form of the task was sometimes altered by changing the shape of the cue. In one experiment, we varied the predictability of a sequence of switches and stays. Results showed a definite cost in reaction time associated with performing a switch, but this cost is virtually eliminated on subsequent stay trials (even when their occurrence is unpredictable). A second study demonstrated that cue lead times of 200ms were enough to eliminate most of the perceptual set switching cost, as well, suggesting that the visual system can rapidly set up a new target template. In contrast, a cue lead time of up to 1000ms was not as effective when switching within the task set. In a behavioral and fMRI examination study, we measured RT and BOLD in four conditions in a blocked design: color switching, task switching, both switching, and neither switching. The RT cost in switching both color and task sets simultaneously was less than the sum of the RT cost in switching either color or task set alone. The violation of additivity in RT suggests that perceptual switching and task switching share common cognitive stages. Further, the two types of switching led to similar regions of activation in the intraparietal sulcus, inferior and middle frontal gyri, supplementary-motor area, and frontal eye fields.
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