A fundamental understanding of the mechanisms of cortical processing requires an examination of the relationships of cortical circuitry, functional architecture, and receptive field properties. Ultimately, this kind of analysis can be utilized to explore the neurobiological basis of psychophysics and perception. At the outset our studies were intended to account for the then known receptive field properties of cortical cells in terms of their underlying circuitry, but surprisingly a good part of the cortical circuit appeared to he in violation of the principles of cortical architecture, and this led us to explore the possibility of new, more complex properties of cortical cells. It has become increasingly possible to relate the responsive specificity of cortical cells, and the circuitry underlying this specificity, to the perceptual capabilities of the visual system by performing analogone experiments on single cells and in human psychophysics.