The retinal reference of the tilt aftereffect

Day and Wade (1969) proposed that visual “normalization” and the visual tilt aftereffect depend upon the gravitational orientation of test and inducing figures and that the retina! orientation of these figures is irrelevant. Their failure to distinguish between “normalization” and aftereffect is pointed out, and an analysis of their experiment suggested that it could not yield data which would unambiguously support either the gravitational or the retinal viewpoint. An experiment was reported in which a tilt aftereffect was found to occur under conditions where inducing and test figures could not vary in gravitational orientation. It was concluded that retinal orientation is a sufficient factor in the tilt aftereffect situation; whether it is a necessary factor or whether gravitational orientation is also sufficient remains to be determined.