Psychometric functions were determined concurrently for detection of simple gratings (luminance sinusoidally modulated with spatial frequency f) and complex gratings (luminance modulated by the sum of two sinusoids, with frequencies f and f′). Results were used to test the hypothesis that the two components of a complex grating may be detected independently. In an extensive experiment with f = 14 cycles/deg, the independence hypothesis was consistently rejected only when
, but rarely rejected when the value of f/f′ lay outside this range. In other experiments, f was between 1.9 and 22.4 cycles/deg. All results are compatible with the assumption that the human visual system contains sensory channels, each selectively sensitive to different narrow ranges of spatial frequencies, whose outputs are detected independently.
© 1971 Optical Society of America
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