Brightness of time-dependent stimuli

Abstract

An earlier study (De Ridder & Theelen , 1983) showed that the brightness of point sources, flashed on an extended photopic background, can be predicted from the impulse response, measured at threshold level. Here we have duplicated the brightness matching experiments, using large (1° ) fields instead of point sources. The results show once again that equal-brightness curves, determined by matching the brightness peaks of a constant reference flash and a test flash of variable luminance and duration, can be predicted from the impulse response. The results imply that the exponent of the power function, which is assumed to describe the relationship between brightness and luminance, is independent. of the flash duration for both point sources and large fields. The fact that the shape of the equal-brightness curve did not depend on flash intensity supports our earlier suggestion that the initial part of the visual system is linear even for large amplitude changes (more than 3 log units above threshold). The brightness matching of a test flash of constant luminance but variable duration with a reference flash of constant duration can also be predicted from the impulse response. It is argued that the deviations, obtained near detection threshold, are due to the fact that the brightness impression is determined by the effective luminance, i.e. luminance above threshold