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.

The effect of numerical magnitude on the perceptual processing speed of a digit.

In this study, we investigated whether the numerical information of a digit would affect perceptual processing speed for that digit. In Experiment 1, participants performed a temporal order judgment (TOJ) task in which they judged the order of two digits presented briefly to the left or right of the fixation point with a short asynchrony. The point of subjective simultaneity (PSS) was significantly shifted such that large numbers had to be presented before small numbers in order to be perceived as simultaneous, implying that small numbers are perceptually processed faster than large numbers. Given the susceptibility of a TOJ task to response bias, this result might have simply reflected the conceptual association between magnitude (e.g., small) and response selection (e.g., first). To exclude the potential influence of response bias, we adopted a simultaneity judgment (SJ) task in Experiment 2. Most participants in Experiment 2 had participated in Experiment 1. The participants judged whether the two digits were presented simultaneously or successively. The maximal possibility of simultaneous response was obtained when a large digit preceded a small digit by 5 ms, suggesting that small numbers were indeed perceived earlier than large numbers. Our findings indicated that small numbers were processed faster than large ones and that perceptual mechanisms contribute to this temporal advantage. In addition, although the TOJ and SJ task produced a similar processing speed advantage for small numbers, the PSSs of the two tasks were not correlated, which implied that different cognitive mechanisms were involved in the two tasks.