Supplementary materials to "The parity judgment SNARC effect: The role of response mapping order and the nature of the instruction"

Previous research has investigated the Spatial Numerical Associations of Response Codes (SNARC) effect as a measure of spatial number coding in relation to mathematics (Cipora et al., 2020, https://doi.org/10.1111/nyas.14355). An issue that arises if one wants to correlate mathematical performance with the SNARC effect, is how individual differences in the SNARC effect are measured. Specific design choices might have an impact on the size of the SNARC effect as an individual difference measure. In the present study we investigated two design choices that have previously been neglected as possible determinants of the size of the SNARC effect as obtained in the parity judgment task. The first determinant that we investigated is mapping order. The odd-even left-right response assignments can be congruent (even-right and odd-left) or incongruent (even-left and odd-right) in terms of linguistic markedness (MARC effect: markedness association of response codes) and might be presented in two different orders (congruent first or incongruent first) possibly affecting the size of the SNARC effect. A second possible determinant is task instruction. Instructions can emphasize parity (judge numbers as odd or even) or emphasize two categories (classify numbers as 1-3-7-9 versus 2-4-6-8) as the basis for responding, perhaps requiring different levels of semantic processing. To investigate the potential impact of these variables, this study used a 2x2 between subject design, resulting in four conditions to verify the effect of mapping order and instructions. The results show that the SNARC effect is not influenced by mapping order or by the nature of the instructions, revealing the parity judgment SNARC effect as a robust marker of spatial number coding useful for individual difference research.