Read, S, Ling, S, & Carrasco, M (2003). Covert Attention Alters Visual Appearance. Vision Sciences Society. Sarasota, FL.

Abstract
Although it has long been established that covert spatial attention improves performance in a number of visual tasks, there is a long-standing debate as to whether attention actually alters appearance. When attention is allocated to a given location via a brief peripheral cue, contrast thresholds along the psychometric function are decreased for the target (Cameron, Tai & Carrasco, 2002). From such findings, it has been inferred that attention actually changes the appearance of an attended stimulus. In this study, we directly tested whether covert attention alters phenomenological appearance. Observers were presented with either a peripheral cue (a small circle flashed adjacent to the stimulus location to elicit transient covert attention) or a neutral cue (a small circle flashed at fixation) for 40 ms. Following a 60 ms ISI, two Gabor patches of either 2 or 6 cpd appeared for 100 ms at 4 eccentricity along the horizontal meridian. One of the Gabors was always presented at 6% contrast (Standard), and the other ranged from 1-12% in contrast (Test). The stimuli were tilted 45 to the left or right. Observers performed an orientation discrimination task for the Gabor that they perceived to be of higher contrast. We assessed appearance by determining which of the Gabor patches observers reported as appearing higher in contrast. Consistent with previous studies, our results show a threshold shift in orientation discrimination accuracy across the psychometric function with attention. The results indicate that attention decreases threshold in the psychometric function not only in contrast sensitivity, but also in appearance. Although suggested by past studies, these results show that visual attention alters the phenomenological appearance of an attended stimulus.