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Non-associative learning
Habituation
Habituation is said to have occurred when repeated presentations of
the stimulus by itself cause a decrease in the response. It is
really the simplest form of learning. For example, a wild goose's
flight response to humans decreases after it turns up from a remote
winter feeding ground to spend the summer on a lake in a popular
park. Compared to its behaviour when it first flew in, it soon
tolerates people approaching it and eventually almost ignores them.
It habituates to the stimuli. Consider a police horse, that is
gradually exposed to more and more of the potentially frightening
stimuli that he will later encounter when out on patrol. The people
delivering these stimuli in training are familiar to him and start
their disturbances at a considerable distance from him. Only when he
is ignoring the rumpus at a certain noise level and a certain
distance will these variables be made more threatening.
The likelihood of habituation and its rate are dependent on the
nature of the stimulus, the rate of stimulus presentation, and the
regularity with which it is presented. Habituated responses show
spontaneous recovery when stimulation is withheld. This means that
exposure to the relevant stimuli must continue at intervals to
prevent the original response (eg a flight response) recurring.
Sensitisation
Sensitisation is the opposite of habituation in that there is an
increase in a response after repeated presentations of the stimulus
by itself. The stimulus has to be intrinsically unpleasant or
aversive. If one recalls the magnified unpleasantness of a dripping
tap when searching for sleep, the effect of sensitisation becomes
clear. Sensitisation can over-ride habituation. For example, if the
police horse had been involved in a road traffic accident every day
for a month, he would reliably become sensitised to motor vehicles
and perhaps even become phobic so that just the sound or sight of
them might be sufficient to send him into a flight response.
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