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During the learning process, concept-models are constantly modified. In this review we consider a case when functional forms of models, '''M<sub>m</sub>'''('''S<sub>m</sub>''',n), are all fixed and learning-adaptation involves only model parameters, '''S<sub>m</sub>'''. From time to time a system forms a new concept, while retaining an old one as well; alternatively, old concepts are sometimes merged or eliminated. This requires a modification of the similarity measure L; ); the reason is that more models always result in a better fit between the models and data. This is a well known problem, it is addressed by reducing similarity L using a “skeptic penalty function,” p(N,M) that grows with the number of models M, and this growth is steeper for a smaller amount of data N. For example, an asymptotically unbiased maximum likelihood estimation leads to multiplicative p(N,M) = exp(-N<sub>par</sub>/2), where N<sub>par</sub> is a total number of adaptive parameters in all models (this penalty function is known as [[Akaike information criterion]], see (Perlovsky 2001) for further discussion and references).
A psychological interpretation of maximizing similarity L is the [[Perlovsky | knowledge instinct]], a drive to learn, to maximize the knowledge.
==Dynamic logic==
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