Evgenija D. Shekhter

Psychophysiological research into achromatic vision in humans and vertebrates displays that light intensity is coded by a two-dimensional “excitation vector”. The components of that vector are responses of brightness and darkness neurons (or, according to another classification, on- and off -neurons). It means that a current sensation of brightness is determined by a corresponding interrelation between activities of those two systems responding in opponent way to light onset and off set. The present research is devoted to testing of a hypothesis asserting that two-module organization of achromatic vision is a universal principle of brightness coding in a wide raw of animals including invertebrates. The paper represents certain results of registration and analysis of electroretinogram and total activity of the optical nerve in snail Helix lucorum to diffuse light fl ashes of different intensities. The obtained experimental data, along with the already existing reference data, allow us to assume that on- and off -systems may constitute the neural basis for brightness coding in the invertebrates. The peculiarity of on- and off -systems in vertebrates is that they are formed already at the photoreceptor level.