Spatial and spectral characterisation of the first and second Stiles–Crawford effects using tuneable liquid-crystal filters

Abstract

A semi-automated bipartite Maxwellian illumination system was used to examine the Stiles–Crawford effects of the first and second kind for the fovea of the authors’ eyes. The illumination was realised with a tungsten–halogen source in combination with tuneable liquid-crystal spectral filters. Visibility and hueshift dependencies were examined spatially and spectrally. They have been found to be in fair agreement with former studies in terms of overall appearance but with a notable reduction in directionality for the blue spectral range. The observations are discussed in relation to recent theory that relates the Stiles–Crawford effect of the second kind to the Stiles–Crawford effect of the first kind via a pigment-specific colour visibility function. The results confirm a direct relationship between the two effects and a reduction in hueshift for narrowband illumination. Differences in the green spectral range remain, however, that may be a consequence of a different directionality of S-cones as compared to the M- and L-cones.