Coulson, Grant, Kenneth Koffer, Valerie Coulson, and Honey Went. 2011. “Positive Reinforcement As a Correlation Between Lever Pressing and Inerease in Frequency of Food Pellet Delivery in Rats”. Mexican Journal of Behavior Analysis 2 (2):165-75. https://doi.org/10.5514/rmac.v2.i2.25267.