Topographic numerosity maps cover subitizing and estimation ranges

Yuxuan Cai,Serge O Dumoulin,Wietske Van Der Zwaag,Wietske Zuiderbaan,Shir Hofstetter,Ben M Harvey,Jelle Van Dijk

doi:10.1038/s41467-021-23785-7

Yuxuan Cai, Serge O Dumoulin + Show 5 more

Open Access

https://doi.org/10.1038/s41467-021-23785-7

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Abstract

Numerosity, the set size of a group of items, helps guide behaviour and decisions. Non-symbolic numerosities are represented by the approximate number system. However, distinct behavioural performance suggests that small numerosities, i.e. subitizing range, are implemented differently in the brain than larger numerosities. Prior work has shown that neural populations selectively responding (i.e. hemodynamic responses) to small numerosities are organized into a network of topographical maps. Here, we investigate how neural populations respond to large numerosities, well into the ANS. Using 7 T fMRI and biologically-inspired analyses, we found a network of neural populations tuned to both small and large numerosities organized within the same topographic maps. These results demonstrate a continuum of numerosity preferences that progressively cover both the subitizing range and beyond within the same numerosity map, suggesting a single neural mechanism. We hypothesize that differences in map properties, such as cortical magnification and tuning width, underlie known differences in behaviour.

Highlights

Numerosity, the set size of a group of items, helps guide behaviour and decisions
We measured BOLD response of neural populations that tuned to small and large numerosities and compared estimated neural numerosity preferences to investigate how different numerosity ranges are represented in the brain. We find that both numerosity ranges are represented in the same topographic maps, and we suggest that differences in neural response selectivity and topographic map properties, such as tuning width and cortical magnification respectively, underlie the different perceptual and behavioural properties of small and larger numerosities
When participants viewed the small numerosity range, i.e., 1–7, we found neural populations tuned to these small numerosities

Summary

Introduction

Numerosity, the set size of a group of items, helps guide behaviour and decisions. Nonsymbolic numerosities are represented by the approximate number system. Prior work has shown that neural populations selectively responding (i.e. hemodynamic responses) to small numerosities are organized into a network of topographical maps. Using 7 T fMRI and biologically-inspired analyses, we found a network of neural populations tuned to both small and large numerosities organized within the same topographic maps. Based on the distinct behavioural performances, a separate system termed object tracking system (OTS)[10] is thought to process small numerosities, typically up to four, known as subitizing range[11]. We have previously shown these populations to respond maximally to numerosities in a small range (i.e., 1–7) and to be arranged in orderly topographic maps[28] We measure their responses to a wider range of numerosities, well into the ANS (i.e., 1–64)

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