Figure 1.

A, Task structure. Each trial began with an auditory preparatory cue indicating which of the two peripheral locations subjects should covertly attend. After a variable SOA, Gabor patches appeared briefly at both locations, coincident with an auditory cue indicating the target stimulus. Subjects reported the orientation of the Gabor at the target location with a button press. In some task blocks, targets were very low-contrast and performance was limited by visibility. In other blocks, targets were high-contrast and performance was limited by the small difference in orientation between target types. This study focused on BOLD activity after the preparatory cue but before the onset of the visual targets. B, Subjects performed better after valid versus invalid preparatory cues, indicating that subjects attended to the location given by the preparatory cue. Behavior is matched across target contrast. Error bars indicate SEM.