Abstract
The apparent brightness with which a light stimulus is perceived is determined not only by the average luminance of the stimulus, but also by its temporal properties. For instance, if the luminance is modulated periodically below the flicker-fusion frequency, the observed brightness appears, in general, to be higher than the observed brightness of an equal-average constant luminance. The pupillary response of the human eye, which seems to be well correlated with the observed brightness, has been analyzed quantitatively as a function of the modulation index and frequency for sinusoidal modulation. Under certain quite general assumptions, it is possible to predict the presence of a peripheral linear low-pass filter in the visual system. It is shown how the characteristics of this linear filter can be determined from the experimental data. The break frequency turns out to be around 9 cps and the high-frequency cutoff has a slope of 18 dB/octave.
© 1968 Optical Society of America
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