Quantity Determination and the Distance Effect with Letters, Numbers, and Shapes: A Functional MR Imaging Study of Number Processing

Accuracy of subjects during the identify and order tasks. The identify task (control) resulted in near 100% accuracy irrespective of stimulus type. Subjects were less accurate when ordering letters compared with ordering numbers and shapes. IFL indicates identify far letters; INL, identify near letters; IFN, identify far numbers; INN, identify near numbers; IFS, identify far shapes; INS, identify near shapes; OFL, order far letters; ONL, order near letters; OFN, order far numbers; ONN, order near numbers; OFS, order far shapes; and ONS, order near shapes.

Regional brain activation when subjects judged the order of letters, numbers, or shapes. The images represent group composite activation maps comparing order trials with identify trials within a particular stimulus type. The red-yellow scale indicates brain regions that were more active in the order trials than in the identify trials (P = .001). The blue-purple scale represents brain regions that were active in the identify trials than in the order trials (P = .001). Rows a–e indicate the section position along the z axis of the Talairach atlas system (40, 32, 24, 12, and 4, respectively). The legend for activation is as follows: sfg indicates superior frontal gyrus; acg, anterior cingulate gyrus; mfg, middle frontal gyrus; prcg, precentral gyrus; ips, intraparietal sulcus; ifg, inferior frontal gyrus; pcu, precuneus; smg, supramarginal gyrus; sog, superior occipital gyrus; cu, cuneus; ins, insula; bg, basal ganglia; c, caudate nucleus; stg, superior temporal gyrus; mtg, middle temporal gyrus; cf, calcarine fissure; mog, middle occipital gyrus; lg, lingual gyrus; R, right; L, left.

Group composite maps compare the three stimulus types (see Methods). The red-yellow scale indicates brain regions that were more active (P = .001) when letters were compared with shapes (L vs S, column 1), when letters were compared with numbers (L vs N, column 2), or when numbers were compared with shapes (N vs S, column 3). The blue-purple scale represents brain regions that were active (P = .001) when shapes were compared with letters (column 1), when numbers were compared with letters (column 2), or when shapes were compared with numbers (column 3). Rows a–e indicate the section position along the z axis of the Talairach atlas system (40, 32, 24, 12, and 4, respectively). The legend for activation is as follows: mfg indicates middle frontal gyrus; acg, anterior cingulate gyrus; prcg, precentral gyrus; ips, intraparietal sulcus; sfg, superior frontal gyrus; ifg, inferior frontal gyrus; c, caudate nucleus; sog, superior occipital gyrus; ins, insula; bg, basal ganglia; stg, superior temporal gyrus; R, right; L, left.