Contrast sensitivity is enhanced at cued and impaired at uncued locations

Spatial covert attention can be voluntarily and involuntarily allocated to select information in a specific area of the visual field in the absence of eye movements. We know that covert attention increases contrast sensitivity at the cued location. What we do not know is how contrast sensitivity is affected at the unattended locations. Generally the fate of stimulus processing outside the focus of attention has been explored using concurrent tasks. In this study, we explored whether a transient peripheral cue affects contrast sensitivity at both cued and uncued locations, in the absence of a concurrent task. Five observers performed a 2AFC orientation discrimination task (target tilted 4 to the left or to the right). An adaptive staircase procedure (QUEST) was used to assess contrast thresholds. In the neutral trials a cue announced the display onset but not the target location. In the experimental trials, a dot appeared briefly above one of two Gabor patches (with spatial frequency of 1, 2, 4 or 8 cpd), which were simultaneously presented for 100 ms on opposite sides of the horizontal meridian at 4 of eccentricity. A post-stimulus arrow was presented to the observer for 300 ms to indicate the Gabor patch to be discriminated. When the cue and the post-stimulus response arrow locations matched, a contrast threshold was computed for the cued location (valid trial); when they did not match the contrast threshold was computed for the uncued location (invalid trial). For all observers, directing covert attention enhanced contrast sensitivity at the cued location compared to the neutral trials; interestingly, contrast sensitivity was impaired by a similar magnitude at the opposite, uncued location.