| 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):
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:
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. |