1. Berger, J., 1986. Wild Horses of the Great Basin. University of Chicago Press, Chicago, IL.
2. Brown, E.L., Deffenbacher, K., 1979. Perception and the Senses. Oxford University Press, Oxford, p. 8ff.
3. Spatial summation of pre-pain and pain in human teeth;Brown;Pain,1985
4. A block to pregnancy in the mouse caused by proximity of strange males;Bruce;J. Reprod. Fertil.,1960
5. Coren, S., Ward, L.M., Enns, J.T., 1999. Sensation and Perception. Harcourt Brace, New York, p. 226.