*** Appendix - Pavlov's model of associative conditioning and a contemporary model (Brembs)

Ivan Pavlov.

Pavlov proposed his stimulus substitution theory to explain the conditioning process: all that happens is that the unconditioned stimulus (US) is substituted for the conditioned stimulus (CS), in eliciting a response. The conditioned response (CR) and unconditioned response (UR) are exactly the same. The animal does not actually learn anything; a new neurological connection is formed in its brain, and nothing more. Subsequent research has exposed the inadequacies of this view:

[I]f simple stimulus substitution were to account for learning, the CR should be identical to the UR. Several observations seem to indicate that this is not the case. Rabbits for instance, respond with swallowing and jaw movements during training in a salivary conditioning paradigm, but fail to show these behaviors during test... Or the CR might include behaviors not present in the UR: Pavlov's above-mentioned dog that showed appetitive behavior towards the bell is one example of motor activity towards CSs paired with food, although activity is not part of the response to food itself. Pigeons peck visual signals for USs that do not elicit pecking...

Moreover, it has been shown that conditioning still does occur if the stimulus-properties of the US are suppressed... Suppression of the response-evoking properties of the US, for instance by applying response attenuating drugs such as curare does not prohibit (sic) learning either ... ruling out direct stimulus-response associations in classical conditioning (Brembs, 1996).

Brembs' biological account of associative learning (1996) is more representative of current thinking: an animal that is being conditioned is learning to re-evaluate stimuli, in relation to its own built-in needs:

Assume an animal struggling for survival: every sensation might provide a clue how to escape a predator, find a mate, explore new food patches, hiding places, etc. In every second it is confronted with potentially dangerous or advantageous situations. The possibility to predict such situations must convey an enormous selection pressure. A very effective way to accomplish this task would be an evaluation mechanism, judging situations according to their 'beneficence' for the individual. With such a mechanism salient internal and external stimulus-arrays extracted from the situation would receive situation-specific rankings on a value-scale in terms of 'good', 'bad' or 'neutral' (1996, p. 22).

Brembs claims that this account is compatible with several current models of conditioning, and can also account for various phenomena - including differences between the CR and UR - that have been observed by researchers who study conditioning. If animals that are being conditioned are judging situations and learning to do something new (e.g. evaluate new stimuli or re-evaluate existing stimuli), then what does this tell us about their cognitive mental states?