The Attentional Mechanism in Spatial Numerical Association of Response Codes: A Top-Down or Bottom-Up Based Processing

The SNARC (Spatial Numerical Association of Response Codes) effect, in that people respond faster with the left-hand side to small numbers and with the right-hand side to large numbers, had inspired intensive studies on spatial-numerical representation and its underlying mechanisms in recent years. Deheane et al. (1993) indicated that there is a mental number line in brain, in which the smaller number located in the left side and the larger number located in the right side. The spatial position of a number is activated automatically when a number was displayed. Attention plays the non-neglectable role in SNARC effect. Top-down and bottom-up driven processing are two important thinking ways. Bottom-up driven theory holds that the spacial characteristics of number are stable. Numerical and spacial information are activated simultaneously, yet top-down driven theory holds that number have no stable spacial characteristics and SNARC effect is output of subjective strategy control according to tasks. Concerning the role of attention in SNARC, majority studies have been focusing on the spatial characteristics of numbers, e.g. whether numbers can elicit attentional shifts automatically. Several studies have found that small numbers shift spacial attention to the left, while large numbers shift spacial attention to the right (Calabria & Rossetti, 2005; Fias et al., 2001; Fischer et al., 2003). In bottom-up driven processing, posterior parietal cortex (PPC) play a key role. But when participants were told to image a right-to-left ruler before response, the SNARC effect would disappeared or even reversed (Ristic et al., 2006). The prevailing view is that number can elicit attentional shifts, but under the mediation of top-down driven processing. However, new emerging evidence contributed to this topic from a completely new angle, e.g. how attentional cues, such as encoding of spatial locations, might activate numerical representations differently. Recently the studies from endogenous and exogenous paradigms in spa