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. Author manuscript; available in PMC: 2014 Nov 19.
Published in final edited form as: J Opt Soc Am A Opt Image Sci Vis. 2012 Feb 1;29(2):A223–A232. doi: 10.1364/JOSAA.29.00A223

Fig. 1.

Fig. 1

A, Sketches of receptive field structure. The receptive field center mechanism is thought to derive from a single cone, but the surround may derive from a single cone type or from a mixture of both cone types. The spatial profile is usually considered as a DOG. B, Hypothetical spatial frequency curves for a DOG profile for luminance modulation. The BPI is defined as R0/Rmax. C, With a cone-selective surround, the spatial frequency tuning curve for a cone-isolating grating targeting the center cone class alone is expected to be low-pass in shape. D, With a mixed surround, a bandpass tuning curve is expected for a cone-isolating grating targeting the center cone class, but with a lesser degree of low spatial frequency roll-off compared to a luminance grating.