Abstract
Visual attention can select relevant visual input on the basis of its location, its status as a segmented object, or its features (e.g., motion, color) by modulating the strength of sensory representations in early visual areas. We investigated the source of feature-based attentional control using rapid event-related fMRI. An aperture was presented containing random dots moving in one of six directions with one of six colors. Direction of motion and color changed randomly and independently once per second. Observers attended to either motion or color at any given time. Two directions of motion and two colors were targets: one direction and one color target instructed them to maintain attention on the currently attended feature; the other direction and color instructed them to shift from the attended feature to the other feature (e.g., motion to color). Previous experiments from our laboratory investigating shifts of attention between locations and between superimposed objects revealed that superior parietal lobule (SPL) emits a transient attentional switch signal that appears to change the attentive state of the observer. The present experiment revealed transient increases in activity in SPL time-locked to shifts of attention between features. These results extend our finding that SPL mediates the control of both spatial and non-spatial shifts of visual attention by issuing a transient attentional switch signal. Funded by NIDA R01-DA13165.