a reinforcer delivered contingent

Rats were trained to respond with intravenous cocaine as the reinforcer under a fixed interval 15-min schedule, during which conditioned stimuli paired with cocaine were presented contingent on ... Contingent: depending on something else that might or might not happen; likely, but not certain to happen (e.g., plans to go to the beach are contingent on the weather) (From Merriam-Webster) Positive ... Nature: Effects of Contingent and Non-Contingent Cocaine on Drug-Seeking Behavior Measured Using a Second-Order Schedule of Cocaine Reinforcement in Rats Effects of Contingent and Non-Contingent Cocaine on Drug-Seeking Behavior Measured Using a Second-Order Schedule of Cocaine Reinforcement in Rats