A field-additive pathway detects brief-duration, long-wavelength incremental flashes.

This paper reports tests of the hypothesis that a 10 mse-c. 667 nm. fovea1 teSt flash, presented upon a steady, 8” background, is detected by a pathway whose sensitivity is monotonically related io a linear functional of photoreceptor quantum catch. The hypothesis is tested by (1) measuring incrementthreshold curves for various background wavelenghts, and (2) measuring threshold upon mixtures of two backgrounds with different wavelengths. The data are consistent, within measurement error, with the hypothesis. We argue, on grounds of plausibility, that the pathway’s sensitivity to the 10 msec test flash is controlled not by an arbitrary linear functional, but by the quantum catch of a single class of photoreceptors.