Brightness distribution across the mach bands measured with flicker photometry, and the linearity of sensory nervous interaction.

Abstract

Since a comparison stimulus produces inhibition, it is difficult to measure lateral inhibition. This is true especially for measurements of the brightness of the white and dark Mach bands. Starting with the observation that no Mach bands are formed on the edge of two surfaces of different colors if the brightness of the two colors are equal, a marker was then developed which allowed the subject to locate a point inside the Mach bands under observation. The flicker method was used to match the brightness of the Mach bands with the brightness of the marker, without the marker introducing any changes in the brightness distribution of the bands. When the brightness of the white band was compared with that of the dark band, it was concluded that the lateral inhibition that produces the Mach bands probably takes place after the receptor organs have transduced the stimuli into electrical activity in the nervous tissue. A transformation is, in general, associated with a compression of the range of the transmitted signal magnitude. This would explain why such different sense organs as those for vision and skin vibrations, show very similar lateral-inhibition patterns, since the inhibition occurs mainly in the more central portions of the nervous system, which seem to work more or less linearly.