Categorization, conceptual conjunction and expertise: a case study from chemistry

Ross, Anne (1991). Categorization, conceptual conjunction and expertise: a case study from chemistry. PhD thesis The Open University.



This thesis tested the adequacy and generality of the prototype view of concepts. The concepts used were drawn from a knowledge rich, scientific, problem-solving domain, that of infrared spectroscopy. Expert and novice subjects' performance on a number of tasks involving these concepts was examined. The composite prototype model predicts that a conjunct will be compositional, that is, will be an additive combination of its constituents. In contrast a rival theory of concepts, the theory-based view, allows that a conjunct may be non-compositional.

The level of semantic memory first activated when classifying a spectrum was found to be less specific for a novice subject than for an expert.

The dimensions along which novices judged the similarity of spectra indicated that they were more perceptual than experts. Novices judged the similarity of spectra drawn from the extension of a conjunctive concept along a dimension unique to those spectra and which was not used to judge the similarity of spectra drawn from the extensions of either of the constituent concepts. That is, novices were non-compositional in their similarity judgements. Experts, in contrast were compositional. This is in the opposite direction to that predicted by Hampton's composite prototype model of conceptual combination.

In a membership judgement task both experts and novices overextended conjuncts, as predicted by the composite prototype model. Novices overextended more than experts. It is suggested that they may be overextending along the dimension found to be unique to the conjunct, for the novice group, in the similarity judgement study.

In contrast to the findings of the similarity judgement study, when asked to rate attribute importance for two concepts and their conjunct novices were more compositional than experts. This is as predicted by the composite prototype model.

It is argued that the overall pattern of results indicates that subjects' performance on categorization and conceptual combination is influenced by their theories of the domain. It is concluded that it is necessary to view concepts as embedded within theories.

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