Fig. 5.

Stimuli for studying the effect of spatial attention (A–C), attention directed to an orthogonal feature (D–F), and orientation-based attention (G–I). For the spatial attention experiments (A–C), the main stimulus (B) was identical to the one used in the 4AFC feature-based attention experiments (Fig. 1E); however, observers were asked to make a different judgment. The informative cue (A) specified the spatial location of 1 of the 4 patches, and observers were asked to report the direction (out of the 4 possible cardinal ones) for that patch. The logic of the color-based attention experiments (D–F) was similar, except the 4 different groups of moving dots were not labeled by spatial location (i.e., which patch they belonged to) but rather by color, and all appeared within the same central patch (E). The informative cue (D) specified 1 of the 4 possible colors, and observers were asked to report the direction of the moving dots that carried that color. Notice that the cued feature, i.e., color, is not the feature that is being mapped for tuning (direction). The logic of the orientation-based experiments was identical to the 4AFC feature-based experiments depicted in Fig. 1, D–F, except we used oriented lines instead of moving dots (H) and the informative cue (G) specified 1 of 4 possible orientations. For clarity, the example stimulus in H shows patches with 100% signal elements, but in the actual stimulus some of the lines within each patch were randomly oriented (see methods).