Abstract

Previous work in contrast constancy¹ has shown that at suprathreshold levels, sinusoidal gratings of equal amplitude are judged equal in contrast across a range of frequencies. If this result applies to broadband scenes whose amplitude spectra fall off as a function of frequency, it suggests that low frequency structures should appear higher in contrast relative to high frequency detail where the amplitude is considerably lower. Unfortunately, experiments using sinusoidal stimuli say little about how frequency selective units integrate across the spectrum. They therefore provide insufficient information to conclude anything about contrast constancy in broadband stimuli. To explore this issue, we had subjects match the contrast in pairs of bandpass noise patterns. The stimuli were generated by filtering white noise into octave wide bands with peak spatial frequency ranging from 0.25 to 32 c/deg of visual angle. Stimuli were judged equal in contrast when they had constant power or variance. In such patterns the amplitude of the peak spatial frequency falls in proportion to frequency. Contrast sensitivity, if defined in the traditional sense of amplitude inverse, will increase as a function of frequency out to 32 c/deg.

© 1991 Optical Society of America