Research Report Parametric effects of numerical distance on the intraparietal sulcus during passive viewing of rapid numerosity changes Daniel Ansari ⁎ , Bibek Dhital, Soon Chun Siong Numerical Cognition Laboratory, Department of Education, Dartmouth College, 3 Maynard Street, Raven House, Hanover, NH 03755, USA ARTICLE INFO ABSTRACT Article history: Accepted 5 October 2005 Available online 15 December 2005 A number of functional neuroimaging studies have revealed that regions in and around the intraparietal sulcus (IPS) are parametrically modulated by numerical distance, whereby there is an inverse relationship between distance and levels of activation. These areas are thus thought to contain the internal representation of numerical magnitude. Nevertheless, it has also been suggested that the IPS is involved in response selection during number comparison tasks rather than the representation of numerical magnitude per se. In order to test the independence of the effect of distance on cortical regions, we employed a passive viewing paradigm. Sixteen right-handed male participants viewed rapidly changing slides containing arrays of squares. By varying the distance between the numerosity presented in separate blocks (8 vs. 8, 8 vs. 12, and 8 vs. 16), we examined which regions exhibit a parametric effect of numerical distance. This analysis revealed such effects in the superior part of the IPS bilaterally as well as the superior parietal lobule and the supramarginal gyrus. In contrast, slides rapidly changing in area but not number (Area constant, Area × 1, and Area × 2) did not yield a parametric effect of distance in these regions. Instead, a reverse effect of area was found in a region of the calcarine sulcus. These findings suggest that areas in and around the IPS are involved in numerical magnitude discrimination in the absence of an explicit task and response requirements. © 2005 Elsevier B.V. All rights reserved. Theme: Neural basis of behavior Topic: Cognition Keywords: Functional MRI Numerical cognition Numerical magnitude Distance effect Intraparietal sulcus 1. Introduction How does the brain enable the representation of numerical magnitudes? Much research into the neural basis of numerical magnitude processing today is related to an influential paper by Moyer and Landauer (1967). In this paper, the authors reported that reaction time is inversely related to the distance between numbers when adults perform relative magnitude comparisons. This so-called “numerical distance effect” has since been studied in young children, infants, and animals (Brannon and Terrace, 1998; Feigenson et al., 2004; Huntley- Fenner and Cannon, 2000; Sekuler and Mierkiewicz, 1977; Xu and Spelke, 2000). The distance effect is well replicated and is thought to reveal important characteristics of the semantic organization of numerical magnitudes. The fact that it can be measured in both animals and preverbal infants suggests that it represents a fundamental property of the way in which numerical stimuli are processed. In this vein, it has been hypothesized that numerical magnitudes are represented on a “number line,” where magnitudes close to each other share more variance in representational signal than those relatively far apart and are therefore harder to discriminate. BRAIN RESEARCH 1067 (2006) 181 – 188 ⁎ Corresponding author. Fax: +1 603 646 3968. E-mail address: Daniel.Ansari@Dartmouth.Edu (D. Ansari). URL: http://www.dartmouth.edu/~numcog (D. Ansari). 0006-8993/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.brainres.2005.10.083 available at www.sciencedirect.com www.elsevier.com/locate/brainres