Affiliation:
1. University of New Brunswick, St. John, Canada
Abstract
Exp. I demonstrated that positive incentive contrast effects in an operant conditioning chamber produced by an increase in the concentration of a saccharine solution in 30 180-day-old rats (older animals) are not found in 30 25-day-old rats (younger rats). Exp. II indicated that the probability of obtaining positive contrast with 60 male albino rats is a positive function of the length of the preshift period.