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Antoine Barbot, Michael S. Landy, Marisa Carrasco; Covert attention affects second-order contrast sensitivity. Journal of Vision 2010;10(7):262. doi: 10.1167/10.7.262.
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Covert spatial attention affects contrast sensitivity for first-order, luminance-defined patterns, increasing sensitivity at the attended location, while reducing sensitivity at unattended locations relative to a neutral-attention condition. Humans are also sensitive to “second-order” patterns, e.g., spatial variations of texture. Second-order sensitivity is typically modeled using a cascade of a linear filter tuned to one of the constituent textures, a nonlinearity (rectification) yielding stronger positive responses to regions containing that texture, and a second spatial filter to enhance texture modulations. Here, we assessed whether covert attention affects sensitivity to second-order, texture-defined contrast. Methods: Stimuli were orientation-defined, second-order, sine-wave gratings. A vertical or horizontal grating was used to modulate between two carrier textures (gratings with higher spatial frequency, oriented at ±45°). Second-order modulator and first-order carrier phases were randomized. Observers judged the orientation (vertical or horizontal) of the modulator. Orientation-discrimination performance was measured as a function of modulator contrast. Stimuli appeared in four isoeccentric locations (5° eccentricity). Exogenous (involuntary) attention was manipulated with a brief peripheral precue adjacent to one of the stimulus locations. Target location was indicated by a response cue after stimulus presentation, yielding three cue conditions: valid (precue matched response cue), invalid (mismatched) and neutral (all stimulus locations precued). Results: Covert attention increased second-order contrast sensitivity at the attended location, while decreasing it at unattended locations, relative to the neutral condition. These effects were more pronounced at high second-order contrasts. The magnitude of improvement was a function of second-order modulator spatial frequency and independent of first-order carrier spatial frequency, and thus could not be explained by increased sensitivity to the carriers. The results indicate that attention improves second-order contrast sensitivity.
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