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Melissa Saenz, Giedrius Buracas, Geoffrey Boynton; Global effects of eature-based attention to direction of motion and color. Journal of Vision 2002;2(7):588. doi: 10.1167/2.7.588.
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We used a divided attention psychophysical task to test the hypothesis that visual attention to a stimulus feature facilitates the processing of other stimuli sharing the same feature. Human observers viewed two separate stimuli presented to the left and right of a central fixation point. Stimuli were circular patches of transparently overlapping fields of upward and downward limited-lifetime moving dots. Subjects performed a dual-task by simultaneously and independently performing a 2IFC speed discrimination task on one field of dots from each side. Thus, without changing the stimulus presentation, subjects could either divide attention across two fields of dots moving in the same direction (both up or both down) or in different directions (one up and one down). Baseline speeds were randomized so subjects could not benefit from comparing speeds across sides. Subjects performed better when dividing attention between fields of dots moving in the same compared to different directions (mean performance across 3 subjects: 78.7% vs. 70.8% correct; p<0.01). In a second analogous experiment, we showed that this attentional effect extends to the feature of color as well. Each stimulus was composed of transparently overlapping fields of stationary limited-lifetime red and green dots. Subjects simultaneously performed a color discrimination task on one field of dots from each side. Subjects performed better when dividing attention between two fields of dots of the same color (both red or both green) than of different colors (one red and one green) (mean performance across 3 subjects: 77.2% vs. 66.4% correct; p<0.01). Together, these results indicate that observers are better able to divide attention across multiple stimuli with common features compared to opposing features. These findings are consistent with an attentional mechanism in which attention to a stimulus feature globally enhances neuronal responses to stimuli throughout the visual field that share that feature.
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