Fig. 1.

Stimuli for studying the effect of feature-based attention on directional tuning. In the 2-alternative forced-choice (2AFC) version of the experiment (A–C), observers saw an informative cue (A) specifying 1 of 4 possible diagonal directions, a stimulus (B) containing 2 patches to the sides of fixation, and an uninformative cue (C) pointing to all 4 possible directions. Each patch contained both “signal” and “noise” dots. Signal dots were fixed in number and all moved in 1 of the 4 possible diagonal directions. Signal direction was always different for the 2 patches, and 1 patch always took the direction indicated by the informative cue. In this example, the signal directions for the 2 patches are indicated by red arrows (not visible in the actual stimulus). Observers were asked to indicate which patch (left or right) moved globally in the cued direction. The 4AFC version of the experiment (D–F) was similar, except the stimulus contained 4 patches (E) and the 4 possible directions were cardinal (up, down, left, and right). Because signal dots in the 4 patches all took different directions, all 4 possible directions were represented in every stimulus but at different spatial locations. For each experiment, we mixed 2 types of trials within the same block: precue trials and postcue trials. On precue trials, the informative cue appeared before the stimulus and the uninformative cue after the stimulus. On postcue trials, the uninformative cue appeared before the stimulus and the informative cue after the stimulus.