Figure 1. Illustration of an example search display.

Participants were asked to make speeded responses toward the orientation of a visual target (a horizontal or vertical line segment). All line segments were surrounded by annuli, whose luminance changed continuously during a trial. On half of the trials the luminance of all annuli followed a sine-wave pattern (as shown in the figure), and on the remaining trials the annuli followed a square-wave pattern. If present, a spatially uninformative tone was synchronized with the target annulus (i.e. the one surrounding the target element). See Movie S1 and Movie S2 for examples of sine-wave and square-wave trials, respectively.