Top-down enhancement and suppression of activity in category-selective extrastriate cortex from an act of reflective attention

Abstract

Recent research has demonstrated top-down attentional modulation of activity in extrastriate category-selective visual areas while stimuli are in view (perceptual attention) and after they are removed from view (reflective attention). Perceptual attention is capable of both enhancing and suppressing activity in category-selective areas relative to a passive viewing baseline. In this study, we demonstrate that a brief, simple act of reflective attention ("refreshing") is also capable of both enhancing and suppressing activity in some scene-selective areas (the parahippocampal place area [PPA]) but not others (refreshing resulted in enhancement but not in suppression in the middle occipital gyrus [MOG]). This suggests that different category-selective extrastriate areas preferring the same class of stimuli may contribute differentially to reflective processing of one's internal representations of such stimuli.

Figure 1

Task design. (A) Refresh condition: Participants first saw a fixation cross, then a face and a scene picture, followed by an arrow cueing them to briefly think back to, or visualize, either the face or the scene, as indicated by the direction of the arrow. (B) Attend condition: Participants first saw an arrow, cueing them to look only at the picture on the left or right side of the screen. This was followed by a face and a scene picture, and then a fixation cross. (C) Act condition: Participants first saw a fixation cross, then a face and a scene picture, followed by a gray square cueing them simply to press a button (and not think about either picture).

Figure 2

Activation in scene-selective areas. (A–G) Activation for each of our seven scene-selective regions of interest across the five conditions of the task (see text for statistical comparisons between conditions). (H) Locations of these regions overlaid on the MNI single-subject template brain. MNI coordinates: L middle occipital gyrus (MOG) = [−33 −90 21]; R MOG = [33 −78 21]; L parahippocampal place area (PPA) = [−27 −42 −15]; R PPA = [33 −42 −12]; L retrosplenial cortex (RSC) = [−15 −57 15]; R RSC = [18 −54 15]; R precuneus (PCu)/intraparietal sulcus (IPS) = [18 −63 54].

Figure 3

Modulation in scene-selective areas. Activation in the four Refresh and Attend conditions is re-expressed here as a modulation index, that is, as a difference relative to the baseline act condition. p values represent one-tailed t tests against zero. Briefly, the PPA was both enhanced and suppressed by refreshing and attending scenes and faces, respectively. RSC displayed a qualitatively similar pattern but only suppression for refreshing faces in left and right (p < .06) RSC, and enhancement for refreshing and attending faces in right RSC, were significant. The MOG showed enhancement for refreshing and attending scenes but suppression only for attending faces. The PCu/IPS was enhanced by refreshing and attending scenes but not suppressed in any condition (see text for additional information). MOG = middle occipital gyrus; PPA = parahippocampal place area; RSC = retrosplenial cortex; PCu = precuneus; IPS = intraparietal sulcus.

Figure 4

Time courses of activity in the bilateral PPA. Signal change over time for the left and right PPA. Time = 0 sec represents trial onset and the attention cue in Attend trials. Face and scene stimuli appear at time = 1.5 sec. Refresh and act cues appear at time = 3.5 sec. As expected, BOLD activity peaks several seconds after face and scene stimuli appear. Enhancement for Attend Scene and suppression for Attend Face (i.e., divergence from act activity) begin earlier (around time = 6 sec) than enhancement and suppression for Refresh Scene and Refresh Face, respectively (which diverge from act around time = 8 sec; see text for additional information).