Bidirectional number-space interactions on the horizontal and sagittal axes

Grade, Stéphane [UCL] Edwards, Martin [UCL] Pesenti, Mauro [UCL]

Recent studies suggest that numbers might be represented spatially, whith small numbers associated with the left and large numbers with the right side of space. However, number-space associations have also been observed with the vertical axis, where the lower part of space is associated with small numbers and the upper part with large numbers, suggesting that number–space associations are not restricted to the horizontal axis. Here, we investigated number-space interactions with horizontal and sagittal (i.e., near-far) space axes. Sixty-four participants took part in the study. They sat in front of a table on which stimuli (i.e., numbers or letters depending on tasks) were displayed on different spatial locations (i.e., left, right, near, or far). They were assigned to one of four groups and asked to: (i) make parity judgments on numbers or consonant-vowel classifications on letters; (ii) report the perceived position of either stimulus; (iii) make magnitude judgments of numbers (standard comparison to 5) or alphabetical position judgments (i.e., before or after the letter “L”); and (iv) perform both the second and third tasks in a same block. Results on Group 1 showed no significant number-space or letter-space interactions for both spatial axes. Groups 2 and 3 showed a number-space interaction, but only for the sagittal axis, with responses being quicker to small numbers in near space, and quicker to large numbers in far space. Finally, the analyses on Group 4 showed also a significant interaction between space and numbers for the horizontal axis. These number–space associations found on various spatial axes are discussed to constrain current models of number representations.