APPEARANCE OF COLORED PATTERNS - PATTERN COLOR SEPARABILITY

We have measured how color appearance of square-wave bars varies with stimulus strength and spatial frequency. Observers adjusted the color of a uniform patch to match the color appearance of the bars in square -wave patterns. We used low-to-moderate square-wave patterns, from 1 t o 8 cycles per degree (c/deg). The matches are not photoreceptor match es but rather are established at more central neural sites. The signal s at the putative central sites obey several simple regularities. The cone contrast of the uniform patch is proportional to square-wave stim ulus strength (color homogeneity) and additive with respect to the sup erposition of equal-frequency square waves containing different colors (color superposition). We use the asymmetric matches to derive, from first principles, three pattern-color-separable appearance pathways. T he matches are explained by two spectrally opponent, spatially low-pas s mechanisms and one spectrally positive, spatially band-pass mechanis m. The spectral mechanisms that we derive are similar to luminance and opponent mechanisms that are derived with entirely different experime ntal methods.