Attentional amplification of neural codes for number independent of other quantities along the dorsal visual stream.

Elisa Castaldi,Manuela Piazza,Alexandre Vignaud,Stanislas Dehaene,Evelyn Eger

doi:10.7554/elife.45160

Abstract

Humans and other animals base important decisions on estimates of number, and intraparietal cortex is thought to provide a crucial substrate of this ability. However, it remains debated whether an independent neuronal processing mechanism underlies this 'number sense', or whether number is instead judged indirectly on the basis of other quantitative features. We performed high-resolution 7 Tesla fMRI while adult human volunteers attended either to the numerosity or an orthogonal dimension (average item size) of visual dot arrays. Along the dorsal visual stream, numerosity explained a significant amount of variance in activation patterns, above and beyond non-numerical dimensions. Its representation was selectively amplified and progressively enhanced across the hierarchy when task relevant. Our results reveal a sensory extraction mechanism yielding information on numerosity separable from other dimensions already at early visual stages and suggest that later regions along the dorsal stream are most important for explicit manipulation of numerical quantity.

Highlights

One largely debated theme in cognitive neuroscience is how the human brain developed the ability to perform mathematics
Given that the whole brain univariate contrasts had confirmed equivalent activations across the two tasks, we further investigated, using multivariate classification, what was the degree of discriminability of activity patterns evoked by different sample numerosities across different regions of the dorsal visual stream and during the number and size task
Our work exploited the enhanced spatial resolution provided by ultra-high field fMRI to reveal how the human brain represents multiple quantitative dimensions of non-symbolic numerical stimuli

Summary

Introduction

One largely debated theme in cognitive neuroscience is how the human brain developed the ability to perform mathematics. The neural substrate subtending this sense of numerical quantity is thought to be shared across species and has been linked to a network of areas in the frontal and parietal cortices sensitive to changes in numerosity since very early in life (Izard et al, 2008; Hyde and Spelke, 2011; see for reviews: Cantlon, 2012; de Hevia et al, 2017) In these areas electrophysiological recordings in monkeys identified single neurons tuned to specific numerosities of visual arrays (Nieder et al, 2002; Nieder and Miller, 2004; Roitman et al., 2007; Nieder, 2016) and fMRI studies in humans found activation in these areas to be modulated during quantity perception as well as during calculation (for reviews see: Arsalidou and Taylor, 2011; Eger, 2016; Piazza and Eger, 2016). Population-receptive field mapping (pRF) methods identified individual locations tuned to specific numerosities arranged in spatially organized maps in the parietal cortex (Harvey et al, 2013)

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