Some principles governing changes in the apparent lightness of test surfaces isolated from their normal backgrounds

When smooth matt test surfaces are suspended by fine threads in a strong illumination gradient and in isolation from any ordinary background, lightness constancy fails. It may be restored by introducing other objects into the field in the same plane as the test surfaces. Using a large number of subjects making independent judgements by a comparison scale method, the present investigation attempts to discover the principles underlying the restoration of lightness constancy by the introduction of inducing surfaces of varied size and reflectance at varied distances from the test surface.