1. BOOHER, H. R. Differential visual depth perception threshold in the hooded rat. Unpublished M. A. thesis, George Washington University, 1967.
2. WALK, R. D. The study of visual depth and distance perception in animals. In D. S. Lehrman, R. A. Hinde, & E. Shaw (Eds.), Advances in the study of behavior. Vol. 1. New York: Academic Press, 1965, pp. 99–154.
3. WALK, R. D., & BOND, E. K. Deficit in depth perception of 90-day-old dark-reared rats. Psychon. Sci., 1968, 10, 383–384.
4. WALK, R. D., & GIBSON, E. J. A comparative and analytical study of visual depth perception. Psychol. Monogr., 1961, No. 75, 1–44, (Whole No. 519).