The means by which one perceives the relative distances of objects in space and their relative orientation constitutes one of the most complex processes of vision. The dioptric images falling on the retinas of the two eyes are essentially flat images, lacking, in themselves, the three dimensional characteristics of the field of the objects observed. Only from the details that make up the pattern of these images on the two retinas can one reconstruct and can one appreciate the depth extent of objects before one's eyes.
According to the current theories of perception, one can attribute the perception of depth, first, to certain psychologic depth motives (psychische Tiefenmotive) that arise from particular characteristics of each of the image patterns and, second, to the unique phenomenon of stereopsis that arises from the differences within the two image patterns on the retinas.
The factors designated as psychologic must be considered empiric; that