Abstract
When given a cue about the color of a search target people can use top-down control to constrain their search and eye movements to only objects of the target color (Williams, 1967). Here we investigate whether people can simultaneously bias their attention to target objects that were defined as having either one of two distinct colors. Participants searched for the leftward facing C among a display of 24 Landolt Cs while we monitored their eye movements. Each C was colored red, yellow, green or blue. In the critical block of trials, participants were told that the target, if present, would be either red OR blue. Reaction time data suggest that the effective set size was the total number of red and blue items, suggesting that people could constrain attention to the union of those two colors. More interestingly, the sequence of fixated items, on target absent trials, showed that participants were not searching through all the items of one color and then all the items of the other color, but were instead fixating back and forth between the blue and red items. Runs analyses and comparisons of the number of shifts from an item of one target color to an item of the other target color support the conclusion that participants create an attentional filter that was selective for the union of the red and blue items. These results suggest that people can simultaneously bias at least two distinct colors.