The unsupervised learning of feature extraction in high-dimesional patterns is a central problem for the neural network approach. Feature extraction is a procedure which maps original patterns into the feature (or factor) space of reduced dimension. In this paper we demonstrate that Hebbian learning in Hopfield-like neural network is a natural procedure for unsupervised learning of feature extraction. Due to this learning, factors become the attractors of network dynamics, hence they can be revealed by the random search. The neurodynamics is analysed by Single-Step approximation which is known [8] to be rather accurate for sparsely encoded Hopfield-network. Thus, the analysis is restricted by the case of sparsely encoded factors. The accuracy of Single-Step approximation is confirmed by Computer simulations.
This article tries to reveal factors which could have contributed to the successful spread of the ancient cult of the Greek god of medicine Asclepius but are difficult to grasp by traditional historiographical methods. More specifically, this article analyses which processes within the human body and mind could be advantageous for the spread of mental representations connected with the cult of Asclepius using the theoretical framework of cognitive sciences (especially Dan Sperber's epidemiology of representations and Andy Clark's concept of extended cognition). The major ritual of the cult of Asclepius is known as incubation. Patients, who visited the god's sanctuaries as supplicants, spent a night in the inner sanctuary (abaton) and it was expected that Asclepius would appear in their dreams performing an immediate cure or giving remedies for their recovery. Also, the temples of Asclepius featured iconographical artifacts (e.g. inscriptions about healing miracles) that could trigger emotional reactions and expectations about the ritual. Results from neurobiological experiments suggest that emotional arousal in combination with subsequent sleep could lead to a vivid and long lasting memory of the previous event. These memories could be therefore prioritized in the person's memory and thus be more suitable for cultural transmission than others.