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UBC Theses and Dissertations

Constrained scaling : calibrating individual subjects in magnitude estimation West, Robert Lawrence


Magnitude estimation, although a very valuable technique for the study of sensory systems, suffers from the problems of excessive intersubject variability and interlab variability (Marks, 1974). Assuming that healthy normal subjects experience approximately the same levelof perceived stimulus magnitude when presented with the same stimulus under the same conditions, the seemingly excessive intersubject variability revealed by magnitude estimation techniques must be due to factors left free to vary during the magnitude estimation procedure. In this dissertation I explore a methodology called constrained scaling, which is an attempt to establish a methodology for magnitude estimation that exerts greater control over the scaling process. Constrained scaling consists of using feedback to train subjects to respond to a set of stimuli according to a power function with a particular exponent and then asking them to respond to a different set of stimuli using the response scale they have learned, but without feedback. Thus this dissertation was an investigation of the degree to which, and under what conditions, subjects could extend a learned scale to novel stimuli. The results indicate that under the right conditions subjects can perform this task with a level of precision sufficient to significantly reduce intersubject variability as compared to standard magnitude estimation results. The consequences of constraining subjects to answer according to a predetermined function are discussed in terms of the type of scale that is produced. Also, the conceptual implications of constrained scaling for modeling sensory systems and conscious perception are discussed.

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