Color perception within a chromatic context: the effect of short-wavelength light on color appearance.

Light at the boundary of a uniform test field (contrast) has a qualitatively different effect on color perception than light in more remote noncontiguous regions (context). Basic properties of color perception with contextual short-wavelength light are assessed here with a 1 degree test field surrounded by either contiguous or noncontiguous 440 or 491 nm light (32 td). Contrasting stimuli are 3 or 5 degrees adapting fields, a thin 1 degree i.d.-2 degrees o.d. (0.5 degree wide) contiguous band, or a large 1 degree i.d.-5 degrees o.d. contiguous surround. Contextual stimuli are a remote 3 degrees i.d.-5 degrees o.d. ring or 0.5 degree wide noncontiguous bands at various distances from the edge of the 1 degree test field (2 degrees i.d.-3 degrees o.d., 3 degrees i.d.-4 degrees o.d., or 4 degrees i.d.-5 degrees o.d. bands). Contiguous surrounds have little influence on color appearance, but remote noncontiguous short-wavelength light strong affects the color of the test field, shifting it toward redness. The shift toward redness increases as a thin 440 nm band is moved farther from the test field (up to 5 degrees), unlike the effect of distance on remote middle- and long-wavelength bands. Measurements comparing the effects of 440 nm and luminance-equated 491 nm light indicate a contribution from S cones.