The Role of Visual Clustering in Approximate Numerosity Perception
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Marupudi, Vijay
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Abstract
The ability to visually perceive distinct objects as groups that belong together is a core part of human perception. This ability, called visual clustering, is important for a wide range of human behaviors such as ensemble perception, visual working memory, spatial problem-solving, and understanding information visualizations. However, surprisingly little is known about this ability, which is also known as Gestalt proximity grouping. In the work presented in this thesis, I found that people showed a high degree of reliability in their visual clustering, with higher reliability on clustered compared to dispersed stimuli. These properties demonstrate the promise of using clustering to solve other visual problems. In human solutions of the traveling salesperson problem (TSP), I found that reliability patterns of the TSP for clustered and dispersed stimuli followed the same patterns as visual clustering, suggesting that clustering may be used to solve the TSP. Additionally, I found that people's TSP solutions were remarkably consistent with their clusterings, with 52% of TSP solutions being perfectly congruent with their clusterings. Even when their solutions weren't perfectly congruent, they displayed high amounts of congruency, providing further support to the theory that people use the clusters they perceive to solve the TSP. Finally, I investigated whether people use visual clustering for numerosity perception by conducting two experiments where participants compare and estimate the numerosities of sets of points while providing the clusterings they perceive. In both experiments, I found a robust effect of cluster structure, i.e., whether stimuli are clustered or dispersed, on the magnitude comparison task. However, other clustering properties, such as the number of clusters, clustering reliability, and how points were assigned to clusters, were not reliable predictors of participants' performance. These findings shed light on the cognitive processes underlying the approximate number system (ANS). They suggest that visual clustering, one prevailing explanation for why people underestimate clustered stimuli, is unlikely to be responsible for the cluster structure effect and raise new questions about the mechanisms underlying the ANS.
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2025-04-23
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Dissertation