Influence of the adapting background on the Broca-Sulzer phenomenon

The influence of the state of adaptation of the eye on the Broca-Sulzer phenomenon has been investigated by measuring equal-brightness curves as a function of flash duration for circular 1°-fields, projected against a photopic and a dark background. The results show that the Broca-Sulzer effect is present in both conditions. In the dark-field condition the Broca-Sulzer effect was found to shift to shorter durations with increasing flash luminance . For flashes presented against the photopic background, however, this shift is absent. Furthermore, the equalbrightness curves were found to be isomorphous. They coincide after translation along the luminance axis in the photopic background condition and after translation along the duration and luminance axes in the dark-field condition. It is argued that both the isomorphism of the equal-brightness curves and the absence of the shift in the photopic background condition confirm our earlier conclusion (De Ridder & Theelen, 1983, 1984) that the exponent of the power function, relating brightness to luminance, is independent of flash duration. The shift of the Broca-Sulzer effect in the dark-field condition is attributed to disturbances of the adaptation level.