[A vector model of the simultaneous contrast of achromatic stimuli]

The vector model of simultaneous brightness contrast for achromatic colours is suggested. The difference of intensities between the test and inducing fields is evaluated in subtracting neurons. The difference is added to the test field activation if the intensity of the latter is greater than that of the inducing field and is subtracted under the opposite conditions. The lightness of the test field is coded by a two-dimensional vector which is composed of excitations of white and grey or black and grey neurons. Single values of lightness are coded by selective lightness detectors.