Unsupervised learning is certainly more psychologically plausible, most likely because humans tend to learn more about nature and life through their own personal experience, as an alternative to by listening to a teacher. For example, suppose there is nobody to inform us which instance to classify into which class, which is, what we should always derive. The patterns in this instance are not labeled with class-labels. There is evidence that unsupervised learning is plausible from a biological point of view too, that is, the way neurons change their connection weights, but we shall look at this paradigm here from an engineering point of view.