There is ample anatomical, physiological and psychophysical evidence that the mammalian retina contains networks that mediate interactions among neighboring receptors, resulting in intersecting transformations between input images and their corresponding neural output patterns. The almost universally accepted view is that the principal form of interaction involves lateral inhibition. A simple and fundamentally different process, involving no inhibitory or subtractive terms, can also account for the physiological and psychophysical findings that have been attributed to lateral inhibition. This process also results in a number of fundamental effects that occur in mammalian vision and that would be of considerable significance in robotic vision, but which cannot be explained by lateral inhibitory interaction.

The simple instrument described in this letter performs the following function. When it is pointed at any object, test pattern, or other form of visual display, the optical distance between the observer and the object can be changed at will while the brightness and visual angle of the object are invariant. Further, the observer sees the object through a pupil of any desired shape and transmittance.

When very intense stimuli in the long-wavelength region of the visual spectrum are viewed continuously, they change in hue from red, through yellow, to green. The relation of the time course of these changes to the intensity of the stimulus is reported.