10
Reactions to reward change
IN establishing that the locale system is integrally involved in reactions to
environmental change we purposely omitted any detailed treatment of reactions to
changes in biologically meaningful items, though this is central to much of the
behaviour we have considered. It is clear from much of the previous discussion that
shifts in reward contingencies can often lead to aberrant behaviour in hippocampal
animals. In the present chapter we shall provide the basis for understanding these
effects.
A wide variety of changes fall under the rubric of reward shifts: changes in the
amount of reward, its quality, its locations, the objects with which it is associated,
and so on. Though we have already discussed many studies incorporating such
changes we have not focused on reward change per se. Certain studies are directly
concerned with this problem; the most obvious of these involve the complete
removal of reward. This leads to what is called the extinction of the behaviour
previously based on that reward.
According to the present theory, both the locale and taxon systems contain
mechanisms which are sensitive to changes in reward conditions and which could
lead to the cessation of inappropriate behaviours. As a way of approaching the
question of the specific effects of hippocampal lesions upon reactions to reward
changes we shall (1) examine the concept of extinction and the general problem of
persistence, (2) consider these in terms of the locale and taxon systems, (3) discuss
the lesion data concerned with extinction, and (4) turn to the general case of any
change in reward contingencies.
10.1. Extinction and persistence
After reviewing the extant theories of extinction, Mackintosh (1974) pointed out that
'traditional S-R theory is … left with no account of the learning process underlying extinction'
(p. 418).
Partly, this results from the tendency to consider extinct