Experiment 1: A. Retinal mapping session.

<p>The observer first fixated a fixation cross for 700 msec. Then a target appeared on the right or left of the fixation point. The target was displayed for 500 ms and then disappeared. A response screen was displayed until observers indicated their response. B. Decision session. The observer first fixated a fixation cross for 700 msec. Then square markers appeared at the three locations to which the observer was permitted to saccade. Once the observer completed the saccade, the target configuration appeared at one of the side locations chosen at random. The observer then judged whether the target was dot-up or dot-down. We compared human performance to performance maximizing probability of correct discrimination. C. Verification session. The protocol was the same as the Decision session except for the addition of a 400 ms phase, before the saccade, where one of the 3 tokens disappeared. This token indicated the position that the observer should saccade to. If the observers made his saccade to another location (fixation position not within a 1° radius of the indicated object) the trial was aborted and replayed later. Actual eye movement data for one trial for one observer is superimposed in red on the stimulus arrays.