Timing of stimulus onset modulates the influence of visual spatial attention on numerical distance effect

Numerical comparison tasks are common in our everyday life. Previous studies found a phenomenon that the performance is better (higher accuracies and shorter reaction times) when the distance between the two-compared numbers is larger (numerical distance effect). Here, we studied the influence of visual spatial attention (exogenous and endogenous attention) on numerical distance effect, and manipulated the stimulus onset asynchronies (SOAs) between the spatial cue and Arabic number (1, 2, 3, 4, 6, 7, 8 or 9) as 200 ms, 400 ms and 600 ms. We asked subjects to compare the presented Arabic number (1, 2, 3, 4, 6, 7, 8 or 9) with number 5, and found significant numerical distance effects in exogenous and endogenous attention, as there were significant differences between different number distances (number distances = 1, 2, 3 and 4), and the RT increased as the number distance decreased. Furthermore, in endogenous attention experiment, the distance effect was stronger for 600ms SOA condition, and the effect was increased with increasing SOAs. However, in exogenous attention experiment, the distance effect was decreased as the SOA increased, and was stronger for 200ms SOA condition. Our results indicate both endogenous and exogenous attention influence the numerical distance effect, suggested the role of spatial attention in number processing.