Stereopsis in normal domestic cat, Siamese cat, and cat raised with alternating monocular occlusion

Normal cats, cats raised with alternating monocular occluders, and Siamese cats were tested for stereoscopic vision using a shadow-casting technique that produced line stereograms. Human subjects were tested with the same apparatus. 1. Normal cats had stereoscopic vision, but AO and Siamese cats did not. 2. Normal AO cats, and Siamese cats all had equal visual activity (about 6 feet of arc) and all could make accurate judgments about the depth of real objects. 3. Normal cats could fuse crossed disparities as great as 50 feet of arc and uncrossed disparities as great as 30 feet of arc. 4. Normal cats could make stereoscopic discriminations with stimulus disparities greater than 1 degree, even though they could not fuse disparities of this magnitude. 5. Both the AO and the Siamese cats exhibited a convergent squint. 6. Human subjects viewing identical stimuli could not fuse stimuli having disparities greater than 10 feet, although they could make depth judgments for crossed disparities as great as 5 degrees. 7. These results imply that animals without binocular cells in area 17 do not have stereoscopic vision, but do not determine if disparity-selective cells in the visual cortex are responsible for stereopsis.