Detecting changes of spatial cone-excitation ratios in dichoptic viewing

Spatial ratios of cone excitations produced by light reflected by different surfaces in a scene may provide the cue for discriminating changes in illu minant from changes in surface reflectances. To test whether these ratios c an be computed across the two eyes, observers were presented with simulatio ns on a computer-controlled monitor of pairs of juxtaposed or separated Mun sell surfaces undergoing an illuminant change with a small change in cone-e xcitation ratios or a change with constant cone-excitation ratios. Surfaces were viewed either binocularly or dichoptically. Observers reliably discri minated the two changes in both viewing conditions, although less well dich optically. Cone-excitation ratios, which may in principle be computed retin ally, may also be computed cortically. (C) 2001 Elsevier Science Ltd. All r ights reserved.