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Lucas Huszar, Antoine Barbot, Marisa Carrasco; How exogenous attention alters perceived contrast. Journal of Vision 2019;19(10):100. doi: https://doi.org/10.1167/19.10.100.
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Introduction: Attention enhances the appearance of low-level visual attributes, such as contrast and spatial frequency (Carrasco & Barbot, 2018). Little is known about how attention modulates the underlying perceptual representations of these phenomenological changes. Here we investigated how exogenous (involuntary) attention alters contrast appearance through psychophysical reverse correlation, in which signal-like fluctuations in noise predict trial-to-trial variability in perceptual judgments. If attention alters appearance by enhancing sensitivity to low-level stimulus attributes, participant’s sensitivity to stimulus energy should differ with attention. Methods: We adapted the appearance protocol (Carrasco, Ling & Read, 2004) for reverse correlation analyses. On each trial, two tilted Gabors embedded in smoothed Gaussian noise were presented simultaneously. Participants were asked to report the orientation of the Gabor of higher contrast. The contrast of the standard patch was fixed at 40%, while the test patch’s contrast varied from 8–100%. Attention was manipulated through peripheral precues. Attention effects were measured by computing the proportion of trials in which participants reported the test patch as higher contrast than the standard patch while cueing either the test or the standard stimulus location. The point of subjective equality (PSE) was estimated for each cueing condition, and compared to the point of physical equality. Using reverse correlation, we assessed whether and how differences in energy sensitivity with attention mediate changes in perceived contrast. Results and Conclusion: Attention shifted the PSEs: cueing a stimulus embedded in noise increased its perceived contrast. Using reverse correlation we could quantify how signal-like fluctuations in noise predict observers’ trial to trial variability in perceived contrast judgments. We found that attention increased observers’ sensitivity to stimulus energy differences between the test- and standard patches, without changes in tuning. These results further our understanging of how attentional enhancement in contrast sensitivity alters perceived contrast.
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