Separable red-green and luminance detectors for small flashes
Kronauer, Richard E.
Eskew, Rhea T.
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Chaparro, A., Stromeyer, C.F., Kronauer, R.E., & Eskew, Rhea T. Separable red-green and luminance detectors for small flashes. Vision Research, 34(6), 751-762. doi: 10.1016/0042-6989(94)90214-3
Detection contours were measured in L and M cone contrast coordinates for foveal flashes of 200 msec duration and 2.3, 5, 10 and 15 min arc diameter on a bright yellow field. The test flash consisted of simultaneous incremental and decremental red and green lights in various amplitude ratios. At all sizes, the most sensitive detection mechanism was not a luminance mechanism, but rather a red-green mechanism that responds to the linear difference of equally weighted L and M cone contrasts, and signals red or green sensations at the detection threshold. Both temporal and spatial integration were greater for red-green detection than luminance detection. A coincident, subthreshold, yellow flash (a luminance pedestal) did not affect the threshold of the red-green mechanism. Such a pedestal is a sum of equal L and M cone contrast--it represents a vector parallel to the red-green detection contour and thus is expected not to stimulate directly the red-green mechanism. When suprathreshold, the coincident pedestal facilitated chromatic detection by approximately 2x at all tested sizes; intense pedestals did not mask chromatic detection. This insensitivity to intense luminance pedestals further indicates that the red-green mechanism has fixed spectral tuning with balanced opponent L and M contrast inputs. This view of fixed spectral weights contrasts with the "variable tuning hypothesis", which postulates that the weights change with spatial-temporal variations in the test stimulus.(ABSTRACT TRUNCATED AT 250 WORDS)
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