Question

1. What explanation does RWMOD provide for why there is no (or little) conditioning of the CS when CS and US presentations occur at random (how does it explain an organisms sensitivity to contingency)?

Answer 1

RWMOD's explanation on classical conditioning:

Rescorla–Wagner model also known as RWMOD :

The Rescorla–Wagner model was created by Yale psychologists Robert A. Rescorla and Allan R. Wagner in 1972. The Rescorla–Wagner model ("R-W") is a model of classical conditioning, in which learning is conceptualized in terms of associations between conditioned (CS) and unconditioned (US) stimuli. A strong CS-US association means, essentially, that the CS signals or predicts the US. One might say that before conditioning, the subject is surprised by the US, but after conditioning, the subject is no longer surprised, because the CS predicts the coming of the US. The model casts the conditioning processes into discrete trials, during which stimuli may be either present or absent. The strength of prediction of the US on a trial can be represented as the summed associative strengths of all CSs present during the trial. This feature of the model represented a major advance over previous models, and it allowed a straightforward explanation of important experimental phenomena, most notably the blocking effect. Failures of the model have led to modifications, alternative models, and many additional findings. The model has had some impact on neural science in recent years, as studies have suggested that the phasic activity of dopamine neurons in mesostriatal DA projections in the midbrain encodes for the type of prediction error detailed in the model.

Blocking effect :

Blocking effect is the conditioning of an association between two stimuli, a conditioned stimulus and an unconditioned stimulus is impaired if, during the conditioning process, the CS is presented together with a second CS that has already been associated with the unconditioned stimulus

Basic assumptions :

1. The change in the association between a CS and a US that occurs when the two are paired depends on how strongly the US is predicted on that trial - that is, informally, how "surprised" the organism is by the US. The amount of this "surprise" depends on the summed associative strength of all cues present during that trial. In contrast, previous models derived the change in associative strength from the current value of the CS alone.
2. The associative strength of a CS is represented by a single number. The association is excitatory if the number is positive, inhibitory if it is negative.
3. The associative strength of a stimulus is expressed directly by the behaviour it elicits/inhibits.
4. The salience of a CS (alpha in the equation) and the strength of the US (beta) are constants and do not change during training.
5. Only the current associative strength of a cue determines its effect on behavior and the amount of learning it supports. It does not matter how that strength value was arrived at, whether by simple conditioning, reconditioning, or otherwise.

The first two assumptions were new in the Rescorla–Wagner model. The last three assumptions were present in previous models of classical conditioning and are less crucial to the R-W model's novel predictions.

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