Catania, A. C. (1986). On the difference between verbal and nonverbal behavior. The Analysis of Verbal Behavior, 4, 2-9.

Catania, A. C. (1998).Learning (4th ed.). Upper Saddle River, NJ: Prentice Hall.

Keller, F. S. & Schoenfeld, W. N. (1950). Principles of psychology. New York: Appleton-Century-Crofts.

Michael, J. (1993). Concepts and principles of behavior analysis. Kalamazoo, MI: Society for the Advancement of Behavior Analysis.

Peterson, N. (1978). An introduction to verbal behavior. Grand Rapids, MI: Behavior Associates.

Skinner, B. F. (1953). Science and Human Behavior. New York: Macmillan.

Skinner, B. F. (1957). Verbal Behavior. New York: Appleton-Century-Crofts.