Figure 1.

Illustration of (a) the sequence of events in the search and the probe trials in Experiment 1 and (b) the singleton displays in all four experiments, with varying set size. Tasks switched after every two trials (SSPPSSPP…), but the stimulus sequence was the same in all trials. Note that in Experiment 3, all trials were probe trials. Each trial's task was indicated by a letter near the fixation mark (R for search task and G for probe task). In all four experiments, there were only four potential singleton and probe locations, which were each marked by four landmark dots.