Abstract
The predominance of the strength of pattern over the strength of suppression during binocular rivalry has generally been defined as the percentage of total time of appearance. Is this fit for an index of the predominance? Theoretically, the strengths of pattern and suppression periodically oscillate throughout the observation period. From this assumption, the best fitting indices of predominance were examined. The simplest model of the visual system was one in which the periodicity of the two originates was expressed by a differential equation. Various indices were examined by the solution of its equation so that a power function of the ratio of the time of appearance to that of disappearance was obtained as the most suitable index of the predominance.