Why two eyes are better than one: the two views of binocular vision.

Despite centuries of research on the topic, the answer to the question "'Are two eyes significantly better than one, independent of stereopsis?" is still uncertain. In this investigation, steps are taken toward answering the question in a behavioral context. Three sets of experiments are reported in which human binocular and monocular performance are compared in a variety of exteroceptive and visuomotor tasks. In all of the experiments, two eyes facilitated performance. The findings suggest that the binocular system is able to detect the matching information, that is, the concordance, in the monocular optic arrays and to use that information to increase visual efficiency. Furthermore, stereopsis was not found to be important in the performance of visuomotor skills in three dimensions when the subjects were free to move their heads. Thus, the results indicate that an important ecological benefit of binocular frontal vision is having binocular concordance, rather than having binocular disparity.