Psychology Science, Volume 47, 2005 (1), p. 10 - 21 The hunt for SNARC WIM GEVERS 1 &JAN LAMMERTYN 2 Abstract The SNARC effect specifically relates small magnitudes to the left hand side and larger magnitudes to the right hand side (e.g. Dehaene et al., 1990; Dehaene et al., 1993). It is certain that cultural characteristics define the SNARC effect: In western cultures small and large numbers are coded in a left-right direction while in Arabic countries magnitude infor- mation is coded from right to left (Dehaene et al., 1993; Zebian, in press). In this sense, reading and writing direction have been considered to be the main determinants of the SNARC effect. Indeed, a number of recent studies support the idea that the mastering of a language (and thus reading and writing direction) biases scanning habit in a favourable di- rection (e.g. Chatterjee et al., 1999; Padakanaya et al., 2002). If this is indeed the case, it is not surprising that the SNARC effect has been found with stimuli other than numbers (Gevers et al., 2004). Related to this, future research could address the question if magnitude and ordinal information are processed by the same mechanism or by different mechanisms with similar properties. However, reading and writing direction alone are not sufficient to explain all SNARC related findings. For instance, it does not allow for an explanation of a vertical SNARC effect as observed by Schwarz and Keus (2004). Apparently, other variables are important in the onset of an association between numbers and space. Furthermore, the existence of a SNARC effect in the vertical dimension could indicate that the number line can be conceptually extended to a number map. Another puzzling question is to what reference frame the SNARC effect is based. Based on the finding of a SNARC effect with both unimanual (Fischer, 2003a) and oculomotor responses (Fischer et al., 2004; Schwarz & Keus, 2004) at this moment an egocentric alloca- tion of the SNARC effect does not seem feasible. On the other hand, both behavioural (e.g. Bächtold et al., 1998) and neuropsychological studies (Veuilleumier et al., 2004) point out that the mental representation of numerical information in itself is of major importance to the SNARC effect. 1 Wim Gevers, Department of Experimental Psychology, Ghent University, Henri Dunantlaan 2, B-9000 Ghent, Belgium; Phone: ++32 9 2646398; Fax: ++32 9 2646496; E-mail: Wim.Gevers@ugent.be 2 Department of Experimental Psychology, Ghent University, Belgium; E-mail: Jan.Lammertyn@ugent.be