One direction? Cultural aspects of the mental number line beyond reading direction

Abstract

Spatial-Numerical Associations (SNAs) refer to the demonstrations of spatial processing of numbers. The Mental Number Line (MNL) is a representation model describing numbers as aligning left-to-right (LR) and was suggested to account for directional biases in participants' responses during numerical tasks. One common behavioral demonstration of this is the Spatial-Numerical Associations of Response Codes (SNARC) effect, which describes faster left-/right-hand responses to smaller/larger numbers, respectively. The MNL, and, consequently, directional SNAs, show variabilities across different cultures. Reading direction is considered to be the main factor in explaining these differences. In line with this, individuals with right-to-left (RL) reading habits show a weaker or even reverse SNARC effect. In the present study, we investigated whether SNAs are influenced not only by reading direction, but also by cultural directional preferences such as drawing lines, arranging objects, imagining objects (i.e., rightward or leftward facing), or representing events in time (i.e., mentally representing the past/future on the left/right, respectively). To test this hypothesis, we measured the cultural directional preferences and the SNARC effect across three cultures in an online setup; German, Turkish, and Iranian. LR preferences in the Cultural Directional Preferences Questionnaire were most prominent in German participants, intermediate in Turkish participants, and least prominent in Iranian participants. In line with this, the LR SNARC effect was strongest in German, intermediate in Turkish, and weakest (but not RL) in Iranian culture. These findings suggest that cultural directional preferences are involved in the emergence of adult SNAs in addition to the reading direction.

Fig. 1

The depiction of the cultural directionality hypothesis which predicts that both reading direction and cultural directional preferences are involved in the emergence of SNAs. Turkish culture is expected to be mixed regarding reading direction and cultural directional preferences. Therefore, we expected SNAs (specifically the SNARC effect) to be less prominent than a consistent LR culture (i.e., German). Also, we expected the SNARC effect to be more prominent in Turkish than a consistent RL culture (i.e., Iranian) based on the reading direction influence. A steeper negative slope represents a stronger SNARC effect

Fig. 2

Items in CDPQ. *Bicycle depictions were designed by FreePik

Fig. 3

The SNARC slopes in PJ (upper panel) and MC (lower panel) across three samples. The SNARC effect is characterized by a negative slope, indicating larger digits were responded to faster with the right than with the left-hand

Fig. 4

The distribution of the unstandardized SNARC slopes in each sample

Fig. 5

Directional Preferences in CDPQ Items