3.8. Modelling Learning
Adaptation is one of the desirable characteristics in behaviour production. Adaptation
in a behaviours production system can be obtained from three main approaches:
preprogrammed adaptive behaviours, learned adaptive behaviours, and evolved adaptive
behaviours (Meyer and Guillot, 1990). In our BPS, the preprogrammed adaptive behaviours
were obtained from the construction of the three layers discussed in Sections 3.5, 3.6 and 3.7,
whereas the learned adaptive behaviours can be seen as a refinement process of these layers.
In this sense, we will refine the functionality of the BPS to provide it with two types of adaption
by learning: (1) associative learning, which allows new behaviours and emergent properties to
arise within BeCA, thus increasing its level of adaptiveness, and (2) a simple reinforcement
learning approach, which allows the motivation degree in the behaviour to be adjusted
dynamically.
3.8.1. Associative learning
All external signals sensed and preprocessed by the perceptual system are projected at
each instant on the External Perceptions level of the cognitive node. Several of these external
signals represent environment stimuli that are able to trigger the execution of either a reflex,
reactive, or motivated behaviours; whereas other external signals are not associated to the
execution of external behaviours. The last type of external signal is frequently known as neutral
stimuli, because these signals do not have an initial meaning for the agent (i.e. they are not able
to produce a behaviour). The associative learning is concerned with the acquisition of meaning
by these stimuli under certain conditions explained below. The two forms of associative learning
to be incorporated in BeCA are classical primary conditioning and classical secondary
conditioning.
Classical primary conditioning can be explained in the following terms: if an initially
neutral stimulus appears before each presentation of an unconditioned stimulus (US), the
neutral stimulus will be associated with the unconditioned stimulus, and this is why now the first
one will be able to produce the same answer produced by the unconditioned stimulus. This
stimulus, initially neutral, is now called conditioned stimulus (CS) (Kandel, 1976; Kandel,
1985).
In BeCA, neutral stimuli initially are not able to form behavioural columns through all
the levels crossed by unconditioned stimuli. In this sense, the principle to model associative
learning in BeCA consists in the modification of the coupling strength values (Fa) of
determined elementary behaviours, in order to form behavioural columns. In this way, the
trajectory through the different levels of the two blackboards initiated by a neutral stimulus
projected on the External Perceptions level of the cognitive node will be able to reach the
Actions level.
The modification of the coupling strengths of elementary behaviours takes place when
the following things occur: (1) a neutral stimulus is projected on the External Perceptions level
of the cognitive node before each projection of an unconditioned stimulus (for example, water
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