The spatial–numerical congruity effect in preschoolers

Number-to-space mapping and its directionality are compelling topics in the study of numerical cognition. Usually, literacy and math education are thought to shape a left-to-right number line. We challenged this claim by analyzing performance of preliterate precounting preschoolers in a spatial–numerical task. In our experiment, children exhibited a spatial–numerical congruity (SNC) effect during a nonsymbolic numerosity comparison (quicker reaction times to smaller sets presented on the left side of the screen and to larger ones presented on the right side). These findings suggest that left-to-right number ordering may also have some sources that are independent of reading and math education. We argue that the current explanations of the spatial–numerical link need to be reconsidered.