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.