Small number preference in guiding attention.

Healthy individuals are usually biased toward small numbers when they are asked to mentally bisect number intervals or generate number sequences. Number magnitude may be represented spatially along a left-to-right mental number line. The preference for small numbers is believed to reflect the leftward spatial bias of this numerical representation. This study examined whether small numbers captured visual attention more than larger numbers. Participants were asked to detect a target pre-cued by a small or a large number. We found that the response was faster when the target was pre-cued by a small number than when pre-cued by a large number, suggesting that visual attention is preferentially allocated to small numbers. In addition, this attentional preference for small numbers was distinct for participants of different educational backgrounds. For science or engineering participants, this small number preference was enhanced by left-hand responding and was positively correlated with the small number preference in a random number generation task, suggesting that the small number preference was attributable to a leftward bias of the spatial representation. For liberal arts participants, however, left-hand responding did not enhance the small number preference and no correlations were found between the attention task and the random number generation task, suggesting that non-spatial processing mediated the small number preference. Our findings show that the small number preference occurs as early as the perceptual processing stage and distinct mechanisms underlie the preference for small numbers for participants with different educational backgrounds.