Karolis, V; (2012) Mapping numerical magnitude into behaviour. Doctoral thesis , UCL (University College London).

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Abstract

The importance of spatial models for numerical representations and the functional relation between number and space in the parietal cortex are suggested by the evidence that numerical information may affect spatial processing. It has been hypothesized that number maps onto a unidimensional continuum, the mental number line, and that number and space share a common metric. An investigation of the metric for numerical magnitudes, whether it is shared with space, and how this relation is reflected in behaviour, represent the main topic of the thesis. The hypothesis of shared metric is evaluated by the experimental work in the context of two topics: a) the subjective scale for numerical representation and b) the origin of spatial numerical interactions in visuomotor behaviour. Chapter 2 addresses an issue whether number, similarly to some physical magnitudes, may be represented on the logarithmically scaled continuum. The method for differentiating between logarithmic and linear hypotheses about the scale for number is implemented using novel variants of the number-line task, with results supporting the linear scaling schema. In Chapter 3, the method of transcranial magnetic stimulation was used to investigate whether the parietal areas, known to process numerical distance and allegedly implementing the mental number line, are involved in ratio scale computations, which are not compatible with mental number line model. Chapter 4 proposes a structural similarity between scales for number and space as a criterion to support the common metric between number and space. The scale analysis of number mapping onto space demonstrated discrepancy between spatial and numerical metrics for the performance in the manual estimation. Chapter 5 was designed to differentiate between the effect of number on the automatic visuomotor adaptation and on the response selection. The results show no evidence for the effect of number on the on-line motor corrections but reveal the signatures of non-sequential number mapping onto space at the stage of response selection. The findings in Chapter 5 are contrasted with the findings from Chapter 6, showing a pronounced effect of spatially non-specific expectations on the speed of the visuomotor coordination and spatial discrimination. The overall results do not support the hypothesis of the common metric for number and space and suggest that spatial models for number are deployed flexibly according to task demands.

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