Eyes and Glass Curtains: Visual Accomodation,the Mandelbaum Effect,and Apparent Size

Abstract

During vehicle operation visual acquisition of information frequently occurs through an interposed surface, e.g., a windscreen. Then the eye may focus either the windscreen or the distant object. Circumstances have been documented where the interposed surface provides a more or less obligatory stimulus to accommodation. The apparent size of an object has been shown to relate to accommodation distance. These experiments investigated the relationship between the trapping of accommodation at a near distance (Mandelbaum effect) and changes in the apparent size of an object. In experiment I, 24 observers reported smaller size with nearer accommodation and larger apparent size with farther accommodation at a better than chance rate. The 12 observers in experiment II showed a consistent diminution of mean apparent size of an object as a screen was moved nearer to them. These two situations provide interposed texture analagous to windscreens. The implications for vehicle control are discussed.