1. Conditioned Inhibition CS B CS C clicks Conditioned inhibition is an internal state that prevents an organism from making some response, like salivation. As an intervening variable, it must be operationally defined. To say that that an organism has acquired a conditioned inhibitory response, two tests must be passed: (1) retardation test; (2) summation test. In these examples, there are 2 CSs:

2. Conditioned Inhibition Retardation Test Experimental Group Control Group Inhibitory training with CS B No experience with CS B Phase 1Phase 2 (test) CS B is paired with US until there is a strong CR. CS B is inhibitory if it takes the Experimental Group more trials to learn a CR than it takes the Control Group. In other words, the previous inhibitory training slows down learning in the Experimental Group.

3. Conditioned Inhibition Why Does the Experimental Group Learn More Slowly? 0 Excitation Inhibition + - Tendency to Salivate to CS B The Control Group starts at 0. Going from Trial 1 to Trial 5, the level of excitation increases.

4. Conditioned Inhibition Why Does the Experimental Group Learn More Slowly? 0 Excitation Inhibition + - Tendency to Salivate to CS B The Experimental Group starts below 0. It takes extra trials to bring them up to 0, then more trials to raise the level of excitation.

5. Conditioned Inhibition The logic is as follows: If you combine a positive value (like +9) with a negative value (like –4), the sum will be lower than the positive value alone. Summation Test The positive value is an “excitatory” CS, a CS that has been paired with the US. The negative value is an “inhibitory” CS, a CS that has been used in some form of inhibitory training. CS C clicks CS B Excitatory stimulus: Inhibitory stimulus:

6. Conditioned Inhibition The Experimental Group receives inhibitory training with CS B. Summation Test Phase 1 The Control Group receives no training with CS B.

7. Conditioned Inhibition Both groups receive pairings between CS C and the US until there is a strong CR. Summation Test Phase 2 clicks

8. Conditioned Inhibition CS B and CS C are combined and presented together for a few trials without the US. Summation Test Phase 3 If CS B is inhibitory, the CR should be weaker in the Experimental group than in the Control group. This is because CS B is neutral (has a value of 0) for the Control group but has a negative value for the Experimental group. Combining a negative CS with a positive CS produces less excitation than combining a neutral CS with a positive CS.