Purposive behaviour requires the learning of appropriate knowledge about the environment. Cognitive theory and techniques used in mathematical psychology are combined in an exploratory study of aspects of a theory of learning. A single quantifiable set of stimuli is used as a preliminary test of the theory and data analysis techniques. A set of 34 features are derived for the stimuli, including scales of complexity and preference. Pairwise similarity judgements are used to assess which of these features are most salient to the perceiver. A delayed similarities task is outlined as a special case of a generalised similarities paradigm. Results obtained in a delayed similarities experiment indicate a shift in the salience of features as compared with corresponding feature salience in a standard similarity judgement experiment. This shift in feature salience is also found when selective attention instructions are given before the similarity judgements are made. Sorting tasks are used to indicate how participants organise (categorise) the Walsh stimuli. The results taken as a whole provide basic information about the way in which the Walsh stimuli are perceived and organised. The present findings need to be checked for their generality using related visual stimuli. Further research within the type of framework to be presented here may eventually lead to a comprehensive theory of learning with respect to two dimensional black and white stimuli.