Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Psychology

Supervisor

Dr. Daniel Ansari

Abstract

Humans are born with a sensitivity to numerical magnitude. In literate cultures, these numerical intuitions are associated with a symbolic notation (e.g..Hindu-Arabic numerals). While a growing body of neuroscientific research has been conducted to elucidate commonalities between symbolic (e.g. Hinud-Arabic numerals) and non-symbolic (e.g. arrays of objects) representations, relatively little is known about the neural correlates specific to the symbolic processing of numerical magnitude. To address this, I conducted the three fMRI experiments contained within this thesis to characterize the neuroanatomical correlates of the auditory, visual, audiovisual, and semantic processing of numerical symbols.

In Experiment 1, the neural correlates of symbolic and non-symbolic number were contrasted to reveal that the left angular and superior temporal gyri responded specifically to numerals, while the right posterior superior parietal lobe only responded to non-symbolic arrays. Moreover, the right intraparietal sulcus (IPS) was activated by both formats. The results reflect divergent encoding pathways that converge upon a common representation across formats.

In Experiment 2, the neural response to Hindu-Arabic numerals and Chinese numerical ideographs was recorded in individuals who could read both notations and a control group who could read only the numerals. A between-groups contrast revealed semantic processing of ideographs in the right IPS, while asemantic visual processing was found in the left fusiform gyrus. In contrast to the ideographs, the semantic processing of numerals was associated with left IPS activity. The role of these brain regions in the semantic and asemantic representation of numerals is discussed.

In Experiment 3, the neural response of the visual, auditory, and audiovisual processing of numerals and letters was measured. The regions associated with visual and auditory responses to letters and numerals were highly similar. In contrast, the audiovisual response to numerals recruited a region of the right supramarginal gyrus, while the audiovisual letters activated left visual regions. In addition, an effect of congruency in the audiovisual pairs was comparable across numeral-number name pairs and letter-letter name pairs, but absent in letter-speech sound pairs.

Taken together, these three experiments provide new insights into how the brain processes numerical symbols at different levels of description.


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