Absolute spectral-threshold functions were measured during the cone-plateau period and in a dark-adapted state at 0, 6, 17, 28, 45, and 65° temporally to the fovea. It was found that, when the photopic functions were brought together at 660 nm, they closely coincided in the 520–700-nm region of the spectrum, irrespective of location, suggesting that the relative spectral sensitivity and the weighted contributions of the middle- and long-wave cone photopigments remain invariant across the retina. On the other hand, the results suggest that the relative contribution of the short-wave cone mechanism increases between fovea and 17°, stays essentially constant between 17 and 28°, and decreases between 28 and 65°. Furthermore, the results suggest that the absolute sensitivity of the middle- and long-wave cones decreases between fovea and 65°, whereas the absolute sensitivity of the rods increases from fovea to 17° and decreases between 17 and 65°. Finally, the log difference between the absolute dark-adapted cone and the rod threshold was found to increase between fovea and 45° and to decrease between 45 and 65°.
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