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Antoine Barbot, Michael S. Landy, Marisa Carrasco; Differential effects of endogenous and exogenous attention on second-order contrast sensitivity. Journal of Vision 2011;11(11):116. doi: 10.1167/11.11.116.
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Covert spatial attention increases contrast sensitivity for first-order, luminance-defined patterns, 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 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 sensitive to texture modulations. Here, we assessed whether and how exogenous (involuntary, transient) and endogenous (voluntary, sustained) attention affect sensitivity to second-order, texture-defined contrast. Methods: Stimuli were orientation-defined, second-order, sine-wave gratings at two of four 5° isoeccentric locations. 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; performance was measured as a function of modulator contrast. Exogenous attention was manipulated with a brief uninformative peripheral pre-cue adjacent to one of the stimulus locations. Endogenous attention was manipulated with a longer-lasting informative central pre-cue. Target location was indicated by a post-cue, yielding valid (pre-cue matched post-cue; exogenous: 50%, endogenous: 67%) or invalid (mismatched; exogenous: 50%, endogenous: 33%) cue conditions. In both experiments, a neutral cue (33% of total trials) indicated that the target was equally likely to appear at any location. Results: Both exogenous and endogenous attention increased second-order contrast sensitivity at the attended location, while decreasing it at unattended locations, relative to the neutral condition. Exogenous attention increased second-order contrast sensitivity for high (1 cycle/deg), but not for low (0.5 cycle/deg), second-order spatial frequency patterns. However, endogenous attention enhanced contrast sensitivity for both high and low second-order spatial frequency patterns, supporting the view that endogenous attention is more flexible.
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