This special corner consists of three selected papers that were presented at the Visual Categorisation and Image Management Systems (VCIMS) workshop organised by V. Bonnardel, M. Oakes and J. Tait and sponsored by the Multimedia Knowledge Management Network chaired by S. Rueger that took place at the University of Sunderland on the 18 June 2006. The VCIMS workshop offered the opportunity to bring together Cognitive Psychologists, Visual Neuroscientists, Information Retrieval scientists to promote integration from interdisciplinary approaches on visual categorisation in natural and artificial systems. Categorization is the ability to determine that an entity belongs to a particular group of objects and by this mean to recognize, differentiate and understand objects. Objects are classified in function of attributes defining their category memberships. There are different theoretical views that specify the nature of category-relevant attributes and the strategy in distinguishing between exemplars and nonexemplars of a given category. In the classical view, categories are mutually exclusive and collectively exhaustive discrete entities. They are characterized by a list of necessary and sufficient attributes, so that any object belongs univocally to one and only one category. More recent theories, such as prototype theory, acknowledge that natural categories are graded and that some members of the category, based on their properties, are more central than others. For these theories it is essential to evaluate the relative relevance of the different properties. Hammer, Hertz, Hochstein and Weinshall propose a novel approach to determine the ‘dimension weighting’ (property relevance) in category learning. In their approach, learning strategies are based on a restriction indicating whether two exemplars belong (positive equivalence constraint, PEC) or not (negative equivalence constraint, NEC) to the same category. PEC differs from NEC on several aspects. PEC specifies within-category variations whereas NEC specifies between-category variations, and if NEC are more common than PEC (i.e., number of pair comparisons from between category objects is larger than that from within category objects) they are less informative. Indeed, if two objects are from the same category, it can be deduced that at least some of the shared dimensions are relevant to that category and all non-shared dimensions are irrelevant, but if two objects from different categories differ by more than one dimension, it is impossible to know which of these dimensions is relevant for discriminating between categories. Probably because of this difference in the amount of information, performances in a categorization task are better in PEC condition. When the amount of information is made equal in the PEC and NEC conditions, participants are divided in two groups: those who used the NEC strategy successfully and those who do not. These individual differences highlight fundamental distinctions between the two strategies. PEC is used more intuitively but not perfectly while NEC is potentially more accurate but not implemented by all participants. Interestingly, a similar asymmetry is observed in machine-learning where NEC is V. Bonnardel (&) Department of Psychology, University of Winchester, Winchester, UK e-mail: valerie.bonnardel@winchester.ac.uk
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