Differential wavelength sensitivity in the receptive fields of sustaining fibers in the optic tract of the crayfish Procambarus

Abstract

Spike discharges were measured at 473 nm and at 573 nm in 40-50 individual sustaining fibers (slowly-adapting units signaling intensity levels over large receptive fields). The units belonged to five of the 14 classes of sustaining fibers recognized by Wiersma and Yamaguchi (1966) on the basis of the positions of their receptive fields. The test wavelengths were selected because they lie near the peaks of sensitivity of the two spectral types of receptor known to be present in the ommatida. Relative sensitivity was measured at 5 ° intervals as the test lights were moved around the eye on various arcs, and the receptive fields were described in terms of contours of equal sensitivity for each wavelength. No large differences in relative spectral sensitivity were observed as a function of position in the receptive field, but there was a consistent tendency for sensitivity to blue light to be relatively greater in the dorsal region of the eye. The difference was modest, generally being 0.5 log units or less. This effect could be caused either by regional variation in the population density of the blue and yellow-green receptors, or by weighting of inputs in the optic neuropile. © 1973 Springer-Verlag.