HeggelundP. The unidimensional conception of simultaneous achromatic contrast.Scand. J. Psychol., 1972,13, 66–70.—The perceptual changes involved in simultaneous achromatic contrast have been presumed to be specifiable as variation in brightness alone. This conception was not supported when attempts were made to produce identical appearance of two achromatic fields, with different inducing luminance, by varying the luminance in one of them. It was possible to match with respect to either achromatic quality or colour strength, but when matched with respect to quality the fields differed in strength, the field of lowest luminance appearing wea