Non-numerical magnitudes such as cumulative area, element size, and density influence the perception of number. How-ever, it is unclear whether interactions between number and non-numerical magnitudes reflect independent representationsthat interface vis--vis other systems (e.g., language) or, conversely, reflect holistic perception of number and other mag-nitudes. In the present work, we found converging evidence that number and cumulative area are perceptually integraldimensions. Whether assessed explicitly (Experiment 1) or implicitly (Experiment 2), perceived similarity for dot arraysthat varied parametrically in number and area was best modeled by Euclidean, as opposed to city-block, distance. Criti-cally, we also found that the integrality of number and area is comparable to other integral dimensions (Exp. 1: bright-ness/saturation; Exp. 2: radial frequency components), but different from separable dimensions (Exp. 1: shape/color; Exp.2: thickness/curvature). In summary, these findings suggest that non-symbolic number perception is holistic, such that theprocessing of non-numerical magnitudes is obligatory.

Children's spatial and numerical skills are highly related, and predictive of concurrent and future mathematical ability (Lourenco et al., 2018). The number line estimation (NLE) task, in which children indicate the spatial positions of numbers on a line, is a commonly used index of spatial-numerical ability. Critically, training studies have demonstrated a causal link between NLE and math ability (Ramani & Siegler, 2008). Nonetheless, there is extensive debate about the role of numerical and domain-general abilities in the NLE task. Here, we used fMRI with young children to assess the neural mechanisms supporting NLE performance. Whole-brain and ROI analyses yielded significant activation in bilateral intraparietal sulcus (IPS) during the NLE task, relative to matched control conditions. Moreover, we found a positive association between neural maturity in bilateral IPS during the NLE task and behavioral measures of math ability (Cantlon & Li, 2013), controlling for analogical reasoning and spatial working memory.

Numerical and spatial skills are highly interrelated, and both contribute to mathematical cognition. Spatial-numerical associations are frequently examined using number line estimation (NLE); however, there is considerable debate about the relative contributions of number-specific and domain-general (i.e., working memory) processing involved in this task. Here, we used functional neuroimaging to examine the processes supporting NLE in adults (n = 47). Participants completed an in-scanner NLE task and number localizer. We found that within left and right parietal number regions, neural activity during the in-scanner NLE task differentially predicted out-of-scanner behavioral measures. Specifically, activity in the left (but not right) posterior intraparietal sulcus (IPS) predicted visuo-spatial working memory, and activity in the left (but not right) anterior IPS predicted performance on an out-of-scanner NLE task. These findings suggest that NLE relies on both spatial-numerical and domain-general capacities supported by left-hemisphere parietal regions, challenging hypotheses about right-lateralized visuo-spatial contributions to number processing.

Over the past two-and-a-half decades, numerous empiricalstudies have demonstrated a relationship between numbersand space. A classic interpretation is that these spatial-numerical associations (SNAs) are a product of a stablemental number line (MNL) in the mind, yet others haveargued that SNAs are a product of transient mappings thatoccur in working memory. Importantly, although the latterinterpretation has no implications for the representation ofnumber, the former suggests that the representation ofnumber is inherently spatial. Here, we tease apart questionsof spatial representation (à la an MNL perspective) andspatial strategy (à la alternative accounts). In a novel place-the-number task, we demonstrate that numbersautomatically bias spatial attention whereas other ordinalsequences (i.e., letters) do not. We argue that this isevidence of an inherently spatial representation of numberand explore how this work may help answer futurequestions about the relationship between space andnumber.