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Title: Unsupervised categorisation and cross-classification in humans and rats
Author: Close, James Owen Edward
ISNI:       0000 0004 2748 6370
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2009
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This thesis examines how stimulus similarity structure and the statistical properties of the environment influence human and nonhuman animal categorisation. Two aspects of categorisation behaviour are explored: unsupervised (spontaneous) categorisation and stimulus cross-classification. In my General Introduction, I raise the issue of the respective roles of similarity and the classifier in determining categorisation behaviour. In Chapter 1, I review previous laboratory-based unsupervised categorisation research, which shows an overwhelming bias for unsupervised classification based on a single feature. Given the prominent role of overall similarity (family resemblance) in theories of human conceptual structure, I argue that this bias for unidimensional classification is likely an artefact. One factor in producing this artefact, I suggest, are the biases that exist within the similarity structure of laboratory stimuli. Consequently, Chapter 2 examines if it is possible to predict unidimensional versus multidimensional classification based solely on abstract similarity structure. Results show that abstract similarity structure commands a strong influence over participants' unsupervised classification behaviour (although not always in the manner predicted), and a bias for multidimensional unsupervised classification is reported. In Chapter 3, I examine unsupervised categorisation more broadly, by investigating how stimulus similarity structure influences spontaneous classification in both humans and rats. In this way, evidence is sought for human-like spontaneous classification behaviour in rats. Results show that humans and rats show qualitatively different patterns of behaviour following incidental stimulus exposure that should encourage spontaneous classification. In Chapter 4,1 investigate whether rats exhibit another important aspect of human categorisation namely, stimulus cross-classification. Results show that the statistical properties of the environment can engender such cognitively flexible behaviour in rats. Overall, the results of this thesis document the important influence of stimulus similarity structure and the statistical properties of the environment on human and nonhuman animal behaviour.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available