What is a visual stimulus?

Abstract

When two stimuli, s_1 and s_2, are added we get that that the amplitudes in (s_1 + s_2) are smaller than the amplitudes in s_1 plus the amplitudes in s_2 when the two stimuli have different phase spectra. Thus, the full amplitudes in the two stimuli cannot be contained in the amplitudes of the combined stimulus. That is, the amplitudes in s_1 and s_2 are reduced when the stimuli are added. When the amplitudes in a stimulus have been reduced it can no longer be held to be the same stimulus. Consequently, it is possible for two stimuli to have the same appearance but have different amplitudes and can, therefore, not to be held to be the same stimulus. This it would seem, has implications for a number of areas among them visual masking, visual crowding and for the adding of noise to stimuli.