Notch filters can alter color contrasts by selectively filtering different spectral bands of the stimulus and have been developed to enhance reddish-greenish contrasts for color-deficient observers with anomalous trichromacy. We examined the effects of such filters on color salience for normal trichromats, using a visual search paradigm where the task was to locate a color target superimposed on a variegated chromatic background, similar to foraging for fruits among foliage. Background colors varied along a bluish-yellowish or purplish to yellow-green (short-wave cone isolating) axis, roughly spanning the range of dominant color variations in arid or lush environments. Target colors sampled a wide range of hue angles and contrasts. Testing was conducted on a computer monitor, with the filter effects simulated by calculating corresponding chromaticities with or without the filter for naturalistic (Munsell) reflectances. The filter evaluated (Enchroma SuperX glasses) was designed to increase color contrast along a magenta-green axis. Consistent with this, search times for targets on the blue-yellow background were significantly faster for the filter condition, because the filter increased the target-background color difference. Alternatively, overall differences in search times were not observed for the S-cone background. The differences on the two backgrounds could be qualitatively accounted for by the relative salience of the stimuli predicted by a perceptual color space (CIELAB). Our results demonstrate the efficacy of the filters for enhancing visual performance for normal trichromats and naturalistic tasks, and illustrate how these effects depend on the potential color characteristics of the environment.
Webster et al. (Wed,) studied this question.