Three frames from a RAT-C session with Harriett, which show: 1. Human approaches but stops before triggering any additional alert behavior. (Human should not cross threshold.) 2. Harriett decides to respond with a very strong calm behavior of reaching toward the hand. (Important: even tiny, subtle, flickering signs of calm behavior are rewarded in CAT.) 3. Human rewards her by retreating.  This sums up the CAT (Constructional Aggression Treatment) method, showing how it works with a rat.  This method uses negative reinforcement: We would like calm behavior to increase (be reinforced). Harriett considers removal of the human to be a reward - this is something she desires. So when Harriett demonstrates a calm behavior, the human takes herself away, which is the aspect of negative (taking something away, out, as in mathematically subtracting).  Negative reinforcement. Reward the rat by giving her the thing she wants: take away the human. Because we remove the human when Harriett demonstrates calm behavior, we reinforce her calm behavior. Meaning she will become more calm over time.  CAT professionals talk about how the animal reaches a switch-over point, where the fearful behaviors become intrinsically friendly.   To me it is awesome that we could help a frightened rat by removing ourselves, which the rat experiences as a reward, and in the end we have a friendly rat who will seek us out positively.
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