"Positive reinforcement" would be a bar which gives some food to a rat who pushes it three times. If a rat is hungry, he pushes the bar enough times to get as much food as he needs. "Intermittent reinforcement" is a bar that gives some food after a random number of presses each time. A rat will push the bar frantically until he's exhausted, even if he's not very hungry. The technique works pretty well on humans too. https://en.wikipedia.org/wiki/Reinforcement#Intermittent_rei...