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Bruce Hansen, Bruno Richard, Aaron Johnson, Dave Ellemberg; Surround suppression of contrast sensitivity with natural scene stimuli. Journal of Vision 2012;12(9):848. doi: 10.1167/12.9.848.
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Contrast sensitivity for Gabor targets is largely suppressed when embedded in a sinusoidal grating surround and presented at eccentricities ≥1° of visual angle, with suppression being narrowly tuned to orientation and spatial frequency (Petrov, Carandini, & McKee, 2005). However, the real-world environment is not narrow-band. The current study therefore investigated whether or not surround suppression of contrast sensitivity for natural scene targets exhibits a narrow tuning to the known statistical regularities of scenes, specifically the power spectrum slope (i.e., contrast distribution across spatial frequency), structural sparseness (i.e., edge density), and orientation bias. Accordingly, all stimuli (targets and surrounds) were selected such that the power spectrum slope was constant at -1.2, -1.8, or -2.6 (i.e., -0.6, -0.9, or -1.3 in terms of the amplitude spectrum). Within each slope constant, the amount of structural sparseness was systematically varied (2-3 levels). Lastly, the oriented content of all the stimuli was fixed (isotropic or anisotropic) across all levels of power spectrum slope and structural sparseness. Target stimuli consisted of variable rms-contrast circular natural scene patches (1.17° diameter) embedded in fixed high rms-contrast natural surround annuli (4.11° outer diameter), and all stimuli were presented at 3° eccentricity. Threshold contrast sensitivity for detecting natural image targets was assessed with a standard spatial 2AFC staircase protocol, either alone or embedded in natural scene surrounds. For isotropic targets and surrounds, the results show that target contrast threshold suppression was significantly modulated by the power spectrum slope and structural sparseness of the targets, but not the surrounds. A similar trend was observed for anisotropic targets and surrounds, except that the structural sparseness of the surrounds significantly modulated suppression. Such findings preclude an account based on simple inter- (or intra-) channel interactions as a function of available global contrast as it relates to the contrast sensitivity function.
Meeting abstract presented at VSS 2012
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