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Ruby Zoe Rodriguez, Joetta Gobell, Stuart Fuller, Marisa Carrasco; Apparent contrast differs across the vertical meridian of the visual field: Visual and attentional factors. Journal of Vision 2006;6(6):225. doi: https://doi.org/10.1167/6.6.225.
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Background: Performance across the visual field differs at isoeccentric locations. Accuracy is better on the horizontal than the vertical meridian, and in the lower than the upper region of the vertical meridian (Carrasco, Talgar & Cameron, 2001). Recently, it has been shown that attention increases the apparent contrast of a stimulus (Carrasco, Ling & Read, 2004). Here we investigate whether attention affects appearance differentially as a function of spatial location.
Methods: Two Gabor stimuli were presented North and South of fixation at 4° eccentricity along the vertical meridian. Observers were asked to report the orientation of the Gabor that appeared higher in contrast. By assessing which stimulus observers perceived as higher in contrast, we obtained appearance psychometric functions and their concomitant points of subjective equality (PSE). These functions were measured both when attention was deployed via an uninformative peripheral cue and when a neutral cue was presented in the middle of the display. Observers were told that the cues were uninformative as to the stimulus contrast or its orientation.
Results: Consistent with previous findings, we found that attention increases apparent contrast. Furthermore, attention's effect on appearance is asymmetric along the vertical meridian. These results differ from prior work on accuracy, which found symmetric attentional performance gains in both North and South locations.
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