Shared characteristics of stereopsis and the purely binocular process

Wolfe and Held (1981) Vision Res. 21, 1755-1759 demonstrated the existence in the human visual system of a purely binocular process. A purely binocular process is defined as a process that responds only to binocular stimulation and not to stimulation of either eye alone. In this paper, some of the characteristics of the purely binocular process are investigated. We find: (1) the process is less sensitive to high spatial frequencies than is the visual system as a whole. (2) It is insensitive to stimuli near the detection threshold for the visual system as a whole. (3) It makes a greater contribution to the appearance of vertically oriented stimuli than to the appearance of horizontally oriented stimuli. (4) The function of the purely binocular process can be disrupted by blurring the image in one eye (artificial anisometropia). Each of these properties of the purely binocular process is similar to the known characteristics of stereopsis. This suggests that the purely binocular process is a necessary stage in stereopsis.