The Mental Number Line (MNL) aligning small-to-large numbers in a left-to-right direction has been proposed as an explanation for the SNARC effect (Spatial-Numerical Association of Response Codes; Dehaene et al., 1993), which describes faster responses to small/large numbers with the left/right, respectively. The MNL and the SNARC effect have been shown to differ between cultures, and reading direction has been considered as the main cultural directional habit explaining these differences. Specifically, the SNARC effect seems to be absent or even reversed in cultures using a right-to-left reading direction (Dehaene et al., 1993; Shaki et al., 2009; Zebian et al., 2005). However, reading direction might not be the only cultural directional habit shaping the MNL. Thus, we investigated the SNARC effect in the two most common tasks (i.e., magnitude classification and parity judgment) in three culturally different samples. Simultaneously, we assessed cultural directional preferences other than only reading direction (e.g., direction when drawing horizontal lines, direction when arranging objects, direction when imagining objects facing rightward or leftward).

The study was run online as preregistered, and after applying all exclusion criteria, the analysis was based on the data from 130 German, 112 Turkish, and 75 Iranian participants. Left-to-right preferences were strongest in German, intermediate in Turkish, and weakest in Iranian participants. In line with this, the left-to-right SNARC effect was strongest in German, intermediate in Turkish, and weakest (but still not reversed, i.e., right-to-left) in Iranian participants. This was the case both in parity judgment (dRT slopes with continuous magnitude predictor from 1 to 9: German: −6.03, Turkish: −3.43, Iranian: −1.69) and in magnitude classification (dRT slopes with categorical magnitude predictor contrast-coded with -0.5 for numbers 1 to 4 and +0.5 for numbers 6 to 9: German: −32.58, Turkish: −27.26, Iranian: −19.42). These findings suggest that, in addition to reading direction, also other cultural directional preferences shape the mental representation of number magnitude.

Bulut, M., Roth, L., Bahreini, N., Cipora, K., Reips, U.-D., & Nuerk, H.-C. (2025). One direction? Cultural aspects of the mental number line beyond reading direction. Psychological Research, 89, Article 37. https://doi.org/10.1007/s00426-024-02038-4

Dehaene, S., Bossini, S., & Giraux, P. (1993). The mental representation of parity and number magnitude. Journal of Experimental Psychology: General, 122(3), 371–396. https://doi.org/10.1037/0096-3445.122.3.371
Shaki, S., & Fischer, M. H. (2024). How do numbers shift spatial attention? Both processing depth and counting habits matter. Journal of Experimental Psychology. General, 153(1), 171–183. https://doi.org/10.1037/xge0001493
Zebian, S. (2005). Linkages between number concepts, spatial thinking, and directionality of writing: The SNARC effect and the reverse SNARC effect in English and Arabic monoliterates, biliterates, and illiterate Arabic speakers. Journal of Cognition and Culture, 5(1–2), 165–190. https://doi.org/10.1163/1568537054068660