Spectral categories in the learning behaviour of blowflies

Abstract

Wavelength discrimination in the flower visiting blowfly Lucilia spec, was investigated in an attempt to elucidate the mechanisms underlying colour vision in this insect. The flies were subjected to a classical conditioning procedure in which they had to discriminate between a rewarded and an unrewarded monochromatic light stimulus. The results reveal large wavelength ranges within which no discrimination occurs, between which, however, a very distinct discrimination is found. The first range consists o f the UV region up to 400 nm (UV). The second range comprises wavelengths between 400 nm and 515 nm (BLUE) and the third range all wavelengths longer than 515 nm (YELLOW). A simple model consisting o f two colour opponent subsystems (R 7 p/R 8 p and R 7 y/R 8 y) can explain these results. Each o f the two subsystems is assumed to evaluate only whether the sign o f the difference between the excitations o f R 7 and R 8 is positive or negative. For the whole system there are thus four possible conditions: p+y+, p+y+, p-y+, p-y-. Three o f them correspond to the experimentally obtained wavelength ranges. The fourth condition (p+y-) might represent a still hypothetical PUR PLE category in which the stimulus is made up o f both short and long wavelengths. © 1993, Walter de Gruyter. All rights reserved.