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Xian Zhang, John Ferrera, Donald C. Hood, Joy Hirsch; The effect of attention and contrast on the BOLD response in V1 and beyond. Journal of Vision 2005;5(8):681. doi: 10.1167/5.8.681.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To investigate the effects of attention on the response contrast function of the BOLD response of the visual cortex, the results of passive viewing were compared to that of a 2-back memory task, which diverted attention.
Methods: A randomly reversing, scaled dartboard display, typically used for multifocal VEP experiments, was presented at 6 contrasts ranging from 0 to 100% during whole brain functional imaging. A central fixation cross, which also served as the target of the task, was presented as a random sequence of red and green 0.5s flashes every 2s. The subjects viewed the display either passively or while performing a 2-back memory task. Thus, there were 12 (6 contrast levels X 2 viewing) conditions. Each of 4 runs contained 12 16s blocks separated with 20s rest periods. 8 subjects participated. The data were analyzed using a mixed effect analysis (FSL software). V1 was determined using standard retinotopic techniques (BrainVoyager).
Results: The response log contrast function of the BOLD activation at the visual cortex was approximately linear for both attention conditions. The BOLD signal from V1 was only slightly reduced under the 2-back condition. However, other brain regions including medial frontal gyrus, insula, higher visual cortex, and cuneus showed large differences between the two tasks. In particular an extensive negative BOLD response (NBR) was observed during the 2-back task. The NBR differed from the V1 positive response in two ways. First,it was not contrast dependent, i.e.the NBR was approximately the same for 0% and 100% contrast. Second, the NBR exhibited a different time course than the positive BOLD signal , ending slightly more abruptly.
Conclusion: Diverting visual attention while viewing a reversing dartboard display appears to exert a minimal affect on the contrast response function in V1. However, an extensive negative BOLD response was induced outside of V1 during the 2-back task suggesting a widely distributed task-dependent mechanism.
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