Deploying the Mental Eye

Three observers performed a task designed to quantify their “pictorial relief” in visual awareness for a photograph of a piece of sculpture. In separate sessions, they were instructed to assume one of two “mental viewpoints.” The main objective was to investigate whether human observers have such command. All three observers could redirect their “mental view direction” by up to 20°. These observers experience “paradoxical monocular” stereopsis, whereas a sizable fraction of the population does not. Moreover, they had some experience in assuming various “viewing modes.” Whereas one cannot generalize to the population at large, these findings at least prove that it is possible to direct the mental viewpoint actively. This is of importance to the visual arts. For instance, academic drawings require one to be simultaneously aware of a “viewing” (for the drawing) and an “illumination direction” (for the shading). Being able to mentally deploy various vantage points is a crucial step from the “visual field” to the “visual space.”