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Pentti I. Laurinen, Lynn A. Olzak, Toni P. Saarela; Testing a neural model of center-surround interaction psychophysically. Journal of Vision 2004;4(8):780. doi: 10.1167/4.8.780.
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Center-surround interactions in contrast processing by neurons in V1 have been explained by assuming two spatially overlapping antagonistic mechanisms. The inhibitory zone has a larger spatial extent, and each mechanism has independent gain control (Cavanaugh, Bair & Movshon, J. Neurophys. 2002). We asked whether this model adequately explains psychophysically measured contrast appearance. To define the extent of the excitatory perceptual contrast summation field, we matched the contrast of a small circular (0.25 deg) grating patch (8 cpd, c = 0.25) to a similar test grating patch of varying diameter (0.25–2deg). As the diameter of the test patch increased, apparent contrast first increased, then decreased at diameters larger than 0.5 deg. We took this reversal as an estimate of the size of the excitatory perceptual summation field. In a second experiment, we matched the contrast of an annular stimulus with 1.0 deg outer diameter and 0.75 or 0.5 deg inner diameter using a variable-contrast 0.25 deg circular patch as a comparison. The center of the annulus test ring was either unmodulated or had the same frequency grating as the annulus, either in the same or orthogonal orientation. The contrast and diameter of the center patch was varied (c = 0.1 −0.5; diameter = 0.25−0.75). Collinear and orthogonal center patches had either no effect, similar effects (enhancement or suppression) or opposite effects on the apparent contrast of the annulus. The pattern of effects was dependent both on the diameter and contrast of the center patch. The model can account for enhancements of apparent contrast in the annulus when any grating patch is added in the center of the annulus. It cannot, however, account for the suppression we observe.
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