ABSTRACT
This chapter discusses the substantial agreement that the concept of perceptual relativism is fundamental and that comparison processes are ubiquitous, if not always obvious. Interdimensional interactions and quantitative percepts are, therefore, the joint characteristics of level 4 of perceptual processing. The chapter organizes stimuli into qualitative patterns on the basis of a single dimension of the stimulus, quantitative estimates of the value of any perceptual dimension depend entirely on comparisons made between two or more aspects or dimensions of the relevant stimulus. It considers how the geometries of size and shape are similarly affected by multidimensional influences. Recently, however, perceptual psychologists have come to appreciate that other aftereffects exist which may not be absolute, but rather may depend or be contingent on multidimensional interactions. Only a few perceptual psychologists seem to appreciate that the luminance of a lighted surface does not decrease with distance.
