The Abney effect refers to changes in the hue of lights as they are desaturated. Normally the purity is varied by desaturating with a ﬁxed spectrum. Mizokami et al. [J. Vis. 6, 996 (2006) [CrossRef] ] instead varied purity by using Gaussian spectra and increasing their bandwidth. Under these conditions the hues of lights at short and medium wavelengths tended to remain constant and thus were tied to a ﬁxed property of the stimulus such as the spectral peak, possibly reflecting a compensation for the spectral filtering effects of the eye. Here we test this account more completely by comparing constant hue loci across a wide range of wavelengths and between the fovea and periphery. Purity was varied by adding either a ﬁxed spectrum or by varying the spectral bandwidth, using an Agile Light Source capable of generating arbitrary spectra. For both types of spectra, hue loci were approximated by the Gaussian model at short and medium wavelengths, though the model failed to predict the precise form of the hue changes or the differences between the fovea and periphery. Our results suggest that a Gaussian model provides a useful heuristic for predicting constant hue loci and the form of the Abney effect at short and medium wavelengths and may approximate the inferences underlying the representation of hue in the visual system.
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