Wavelength Discrimination Measured with Square-Wave Gratings*

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Abstract
Wavelength discrimination was measured from 480 to 660 nm using wavelength-modulated square-wave gratings. When adjacent grating bars are matched in brightness, wavelength-difference thresholds in all regions of the spectrum increase with spatial frequency within the range of 2.4–19.9 cycles per degree (cpd). Unlike luminance-modulated gratings, no sign of low-frequency attenuation was found. Wavelength differences alone do not yield good visual acuity. Small brightness mismatches between adjacent grating bars generally improve wavelength discrimination and cause low-frequency attenuation in the wavelength modulation vs spatial-frequency function so that it resembles conventional luminance modulation vs spatial-frequency functions.