Langton, C. G., & K. Shimohara, eds., Artificial Life V: Proceedings of the Fifth International Workshop on the Synthesis and Simulation of Living Systems (Cambridge, MA: Bradford Books, 1997), pp. 34–42.
Walter, W. G; Cooper, R.; Aldridge, V. J.; McCallum, W. C.; Winter, A. L. (1964). "Contingent Negative Variation: an electric sign of sensorimotor association and expectancy in the human brain". Nature. 203 (4943): 380–384. doi:10.1038/203380a0. PMID14197376.
Walter, W. G; Cooper, R.; Aldridge, V. J.; McCallum, W. C.; Winter, A. L. (1964). "Contingent Negative Variation: an electric sign of sensorimotor association and expectancy in the human brain". Nature. 203 (4943): 380–384. doi:10.1038/203380a0. PMID14197376.