現象的明るさに及ぼす刺激強度並びに形態の影響 (1)

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Most of the studies on brightness contrast have been carried in a dark room and concerned only with a brightness gradient between the test field (TF) and the inducing field (IF). But, in these cases, the influence of background (Bg) had not been taken into consideration as a factor to affect the brightness of both fields. To obtain a thorough understanding of contrast phenomenon, however, the interaction among these TF, IF and Bg should be examined in detail. Although Benary, W., Fuchs, W. and others emphasized the importance of the configurational rather than the physical factors, they nevertheless failed to pay special attention to the above mentioned interaction.In the present study, the change in the apparent brightness of the surface color (TF) was experimentally investigated in relation to the brightness of adjacent regions (IF and Bg) and the configurational factor (stimulus constellation). The following are the results obtained in the experiments wherein the achromatic colors were used as the stimuli.1) The brightness contrast observed between surface colors on the white background was discovered to be very similar in tendency to that between transmitted lights in a dark room. Namely under one of such conditions as a decrease of brightness of the IF, an increase of the area of the IF and a decrease of the spatial distance between the TF and the IF, the contrast effect in creased. The interaction among these factors was also examined. As the spatial distance went beyond a certain limit, the influence of the other two factors almost diminished (Figs. 4, 5, 6 and 7).2) Even if the brightness of the IF was kept constant, the contrast effect changed with the variation of brightness of the Bg. The brightness of the TF adjusted by subjects depended, therefore, not solely upon the conditions of whether the IF was brighter or darker than the TF, but rather upon that of whether it was brighter or darker than the Bg. In other words, the contrast effect increased with an increase in the brightness gradient between the IF and the Bg. Two types of the contrast effect were observed in the TF, the one tending toward the brighter value and the other, toward the darker. They yielded different types of curves as a function of the IF or of the Bg (Figs. 8 and 9).3) In such a stimulus constellation, where the phenomenon of assimilation should take place according to Fuchs, it was not always observed. Whether the influence of an IF upon a TF takes the form of contrast or of assimilation seems to depend upon the brightness gradient and the spatial distance between them, and also upon the brightness of the Bg. It is suggested on the basis of this experiment that there are two kinds of potential tendencies operating simultaneously, i.e., the one toward contrast and the other toward assimilation, though in general the former is dominant over the latter. In this type of experiment, the influence of the set of subjects cannot be overlooked as indicated by the variation of the results among the subjects (Figs. 10 and 11).