The SNARC effect reflects an association between space and number representations, suggesting a mental number line. Horizontally, the number line is oriented from left-to-right while vertically, the number line is oriented from bottom-to-top. The horizontal SNARC effect seems to be related to finger counting habits, especially in left-hand starters. The present study aimed to investigate how finger counting habits affected the horizontal and vertical SNARC effect in parity and magnitude comparing tasks carried out by Italian adults. After a finger counting questionnaire, left- and right-starters were selected. Participants performed parity and magnitude comparing tasks with horizontal and vertical response key assignments. In both tasks, the SNARC effect was found for both spatial orientations. However, right-starters exhibited significant regression slopes compared to left-starters in all conditions. The results are discussed taking into account the relationship between finger counting habits and SNARC effect in horizontal and vertical orientations.
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