The Apparent Colors of Surfaces of Small Subtense—A Preliminary Report*

Abstract

The early observations of König on the apparent tritanopia of the central fovea were confirmed by Willmer and Wright. Hartridge showed that the small size of the test field, rather than the location of its image on the retina, leads to the tritanopia. In the present work, twenty colors around the Munsell 5-plane were observed against a dark grey background at an angular subtense of 2 minutes and 1 minute of arc, under Macbeth (6800°K) daylight. They were matched with a complete chart of the 5-plane on a similar background and under the same illumination, a mask being provided for the isolation of one color. The phenomenon is somewhat personal but its main features are beyond question. The locus of the “reduced” colors approximates an ellipse with its long axis in the general direction red to blue-green but differing in eccentricity for different observers. The displacement of most of the colors is approximately towards or away from the blue end of the spectrum. There is evidence that the phenomenon cannot be explained by the effect of the macular pigment, but the “dominator-modulator” theory of Granit would seem to offer an explanation for it.