# Effect of observer translation on a small patch of the image

Translation of the eye/camera changes the optic array. For a small patch, this gives information about the magnitude and direction of slant of the surface (see Fig). Taken together with the information about relative visual direction, this allows a binocular observer, or a monocular observer translating small distances, to fixate surfaces and make judgements about their tilt and slant relative to the line of sight [1]. The information stored could contribute to what Marr described as a 2$\frac{1}{2}$D sketch [2], i.e. one that is quite closely related to retinal images and yet it survives eye movements and small head movements.