Abstract
It is unknown whether exogenous attention facilitates cortical processing of attended information, suppresses processing of unattended information, or some combination of the two. In order to test this, we recorded EEG while participants (N = 19) performed a cross-modal attentional cueing task that included peripheral auditory cues that oriented attention to the left and right side of space as well as central “no-shift” cues that did not trigger a spatial shift of attention. This allowed us to apply a cost-benefit analysis to separate facilitatory from suppressive effects in behavioral performance as well as neural activity. Participants performed a visual discrimination task and reported the orientation of a tilted visual target that was presented briefly after the cues. Target discrimination accuracy following valid cues was higher than following invalid cues as well as central no-shift cues (ps < 0.003), consistent with behavioral benefits at the attended location and no costs at the unattended location. Mirroring this behavioral pattern, peripheral cues elicited a greater positive deflection in the EEG signal over visual cortex contralateral vs. ipsilateral to the cued side (p < 0.001), and the contralateral waveform differed reliably from the waveform elicited by the central no-shift cues (p < 0.001) with no difference between the central and the ipsilateral waveforms (p = 0.46). This suggests that visual-cortical processing was boosted at the attended location, with no signs of suppression at the unattended location relative to baseline. Furthermore, we observed a sustained bilateral positivity at frontal sites following peripheral vs. central cues (ps < .001) that represents a novel index of exogenous spatial attention. Overall, our data demonstrate that the exogenous orienting of spatial attention results in visual-cortical enhancement at the location of a salient cue but does not result in spatially specific suppression of visual processing at uncued locations.