BOLD activity in several regions modulated with subjects’ expectations concerning target contrast and/or the locus of spatial attention. The inflated brain in the middle panel indicates regions outside of visual cortex most active following the preparatory cue. Upper and lower panels plot timecourses from four of these regions prior to visual target onset. Activity in both FEF and IFS was significantly higher when subjects expected low contrast targets versus high contrast targets; furthermore activity was significantly higher in both FEF and IFS following cues to covertly attend to the contralateral versus the ipsilateral hemifield. Preparatory activity in pIPS was significantly modulated by the direction of the preparatory cue but did not depend on whether subjects anticipated low or high contrast targets. Activity in STG, presumably related to auditory processing of the preparatory cue, modulated with neither cue direction nor target contrast. Red captions indicate significant effects from an ANOVA over the preparatory timecourse using subjects as a repeated measure (Cue Direction X Contrast X Time; + p=0.057; * p<0.05; ** p<0.01; *** p<0.001). Timecourses are averaged across subjects and hemisphere. The error bar on each graph indicates the average SEM averaged across conditions and timepoints.

Activity in regions derived from independent localizer scans confirms that BOLD activity for unattended but not attended locations is more suppressed during low versus high contrast blocks. Activity in portions of visual cortex representing locations that were always unattended (left panels) is always more suppressed during low contrast relative to high contrast blocks. Activity in portions of visual cortex corresponding to target locations (right panels) depends on which target was attended, driving a significant interaction between cue direction and contrast. When attention is directed towards the location not represented by the region (orange lines), activity is more suppressed during low contrast blocks relative to high contrast blocks, as is the case for all unattended locations. When attention is directed towards the location represented by the region (green lines), activity is not affected by contrast of the upcoming target. Red captions indicate significant effects from an ANOVA over the preparatory timecourse using subjects as a repeated measure (Cue Direction X Contrast X Time; * p<0.05; ** p<0.01). Regions were defined by independent localizer scans and are projected onto a flattened representation of posterior occipital cortex using the PALS atlas (Van Essen et al., 2001). Black lines are approximate borders between retinotopic visual areas based on a standard atlas (Van Essen, 2002). The error bar on each graph indicates the average SEM averaged across conditions and timepoints.

(A) Task structure. Each trial began with an auditory preparatory cue indicating which of two peripheral locations subjects should covertly attend. Following a variable stimulus-onset-asynchrony (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 following the preparatory cue but prior to the onset of the visual targets. (B) Subjects performed better following valid versus invalid preparatory cues, indicating that subjects attended to the location given by the preparatory cue. Behavior is matched across target contrast.

Preparatory activity in portions of visual cortex representing unattended locations is more suppressed in low contrast versus high contrast blocks. Panels (A) and (B) represent mean BOLD activity, independent of target contrast, following auditory cues indicating the subjects should covertly attend to the upper left or upper right in preparation for visual targets. Black outlines indicate the portions of early visual cortex (V1-V4) corresponding to the target locations, as determined from independent localizer scans. Panels (C) and (D) indicate the difference in preparatory activity in visual cortex in low contrast versus high contrast blocks, following leftward (C) or rightward (D) cues. Note that preparatory activity in most of visual cortex is lower in low contrast blocks versus high contrast blocks, suggesting extra suppression of the unattended field in low contrast blocks. This extra suppression largely spares the portion of cortex representing the attended location. Data maps are summed over the last two pre-target MR frames (frames 5 and 6), smoothed with a 5 mm FWHM Gaussian kernel, averaged across subjects, and projected onto a flattened representation of posterior occipital cortex using the PALS atlas (Van Essen et al., 2001). White lines are approximate iso-eccentricity lines based on an average of six subjects from another study (Jack et al., 2006).

Greater suppression of preparatory activity in visual cortex corresponding to the unattended central visual field predicts accurate performance for low contrast trials with leftward targets. The error bar indicates the average SEM averaged across conditions and timepoints.