What are associations made between?
The notion that associations might not be made to responses but to the motivational states that normally provoke those responses, raises the question of whether associations in general are being made between events, that is, stimuli and responses, or between their representations in memory. Asserting that associations are made between appropriate motivational states is really just the first step towards asserting that associations are made between representations. Examining the development of CRs and the way they come to differ from URs provides evidence that associations are made between the motivational states associated with stimuli and responses, and not simply with the stimuli and responses themselves. As mentioned earlier, URs and CRs might differ. One part of the UR to a US of electric shock is an increase in heart-rate. In a well trained animals, however, the CR they make to a CS which predicts shock is a not an increase, but a decrease, in heart-rate. Similar effects are found in CRs conditioned to drug USs. For example, if a tone is repeatedly paired with administration of analgesic doses of morphine the CR to the tone alone is not the decrease in pain sensitivity produced by morphine, but an increase in pain-sensitivity which might be thought of as compensating for the analgesic effects of morphine. These antagonistic CRs certainly fit in with a model of conditioning in which the motivational states associated with stimuli, rather than the stimuli themselves, are associated. Other experiments on blocking indicate that more general representations of the qualities of stimuli are being associated. Bakal, Johnson & Rescorla (1974) added a third group of subjects to a standard blocking experiment, who, rather than being conditioned with the same US in both training phases were conditioned with two different USs, both aversive. This change of USs had little influence on blocking, both groups failed to learn an association with CS2 during the second phase of the experiment. The explanation proffered was that, rather than learning that CS1 predicts a specific type of aversive event, it became a good predictor of aversive events in general. 

Bakal, Johnson & Rescorla's (1974):
Phase 1 Phase 2 Test
CS1-CS2-Klaxon CS2
CS1-Klaxon CS1-CS2-Klaxon CS2
CS1-Shock CS1-CS2-Klaxon CS2

One might argue that this is not so different from arguing that an association has been made between CS1 and the motivational state of fear which both USs (the klaxon and the shock) evoked. A refinement of this design by Dickinson strengthens the case that associations are made with quite general properties which form parts of the representation of events rather than specific motivational states. Dickinson trained animals to expect a positive event to happen regularly (receiving some food: US+) and then showed that associating a CS with the omission of this expected nice event (CS1 in group 'a' signals that CS3 will not be followed by US+) could block learning when this CS was paired with a second CS (CS2) and an aversive US (US-) during the second phase of the experiment. The appropriate controls are ones in which CS1 is experienced with postive consequences in phase 1 (group 'b') and where CS1 has never been experience before phase 2 (group 'c'). 

Dickinson & Dearing's 1979 experiment:
group Phase 1 Phase 2 Test
a CS3 US+
CS3 CS1 
CS1 implies no US+
b CS3 US+
CS1 implies US+
c CS3 US+ CS1 CS2 US- CS2
CS1 is unpredictive

This result is very hard to explain in terms of association with a specific motivational state, but quite straightforward assuming that CS1 has been associated with events having bad consequences in general. 

This document has been restructured from a lecture kindly provided by R.W.Kentridge.