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Steven Buck, Joris Vincent, Tanner DeLawyer; Both context and contrast can induce brown. Journal of Vision 2013;13(15):P9. doi: 10.1167/13.15.44.
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© ARVO (1962-2015); The Authors (2016-present)
A bright contiguous surround (1) changes the hue of a test stimulus from yellow to brown and (2) shifts its red/green equilibrium point (contrast effects). Bright non-contiguous surround features can also produce (1) and (2), even when the test is directly surrounded only by black. We describe the spatial dependence of these context effects.
Six observers viewed an intermittent 2°-diameter foveal test disc surrounded by continuously presented full-screen black or white or by single concentric white rings that were either contiguous with the test or left a black ring (gap) next to the test of 0.25° to 3° width. All white surround features were 140 cd/m2. For each surround, observers (1) assessed the strength of induced brown by adjusting test luminance to the upper boundary of brown and (2) adjusted the ratio of R and G CRT phosphors at equiluminance (21 cd/m2) to yield equilibrium yellow/brown.
Six observers showed significant differences between the smallest black gap and the solid-white conditions for both strength of induced brown and R/G equilibrium (contrast effects). Most observers also showed significant differences between the largest black gap and the solid-black condition for both measures (context effects). Equilibrium R/G was statistically independent of black gap width, while strength of induced brown declined with black gap width up to about 1°.
Thus, both contrast and context strengthen brown and shift equilibrium R/G. The spatial dependence of strengthening of brown differs from that for shift of equilibrium R/G.
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