Experimental stimuli. Targets used in experiments 1 (a) and 2 (b) are shown, as are example trials from experiments 1 (c) and 2 (d). In (c) and (d), the subject’s scanpath is shown; the target is marked red for expository purposes. Light gray orthogonal bars indicate the total duration of the fixation at the corresponding location; a duration of 200ms is indicated by the dashed reference line in each plot. In (c), trials from subject pp in the Easy (top), Medium (middle) and Hard (bottom) conditions are shown. In (d), trials from downward (left) and upward (right) searches are shown. The upward search trial in (d) is a transient target trial; the location of the eye at the time of target onset is indicated by a red strikethrough disk in the scanpath.