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Marisa Carrasco, Anna Marie Giordano, Brian McElree; Temporal dynamics of covert attention. Journal of Vision 2005;5(8):232. doi: 10.1167/5.8.232.
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Background: Covert attention increases discriminability and accelerates the rate of visual information processing (Carrasco & McElree, 2001). In addition, covert attention eliminates the temporal processing asymmetries that exist along the meridians of the visual field (i.e., temporal performance fields: information accrues faster in the horizontal than vertical meridian and in the North than South locations; Carrasco et al., 2004). Here we examined whether the effect of attention on information accrual varies with eccentricity (4° vs. 9°) and with search type (feature vs. conjunction).
Methods: We collected time-course functions for orientation discrimination with the response-signal speed-accuracy trade-off (SAT) procedure. Each trial began with a cue (67 ms), peripheral (a circle adjacent to target location) or neutral (a circle at fixation). After a 53 ms ISI, a 2-cpd target Gabor patch (tilted either to the right or left) and 0 or 7 distracters appeared for 40 ms at 8 equidistant locations from fixation at 4° or 9° eccentricity. In the feature task, all distracters were vertical 2-cpd gratings. In the conjunction task, some distracters shared the orientation of the target and others shared its spatial frequency: the 2-cpd distracters were vertical patches; half the 8-cpd distracters were tilted to the left, and half to the right. To measure discriminability and information accrual conjointly from chance to asymptote, a tone sounded at 1 of 7 SOAs, ranging from 40 to 2000 ms, prompting observers to respond.
Results: For all observers, information processing was faster at 9° than 4°, consistent with our previous findings. Covert attention increased discriminability and accelerated information accrual similarly for near and far eccentricities and for both feature and conjunction searches. In contrast to the compensatory effect of covert attention on temporal performance fields, covert attention did not eliminate speed differences across eccentricity.
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