Numbers and space: a cognitive illusion?

This study investigated the relationships between numerical and spatial representations by means of a bisection task, exploring the view that the core representation of number meaning is spatially organized as a mental number line. In Experiment nos. 1 (bisection of digit strings) and 2 (bisection of flanked lines) spatial biases towards the larger digit were found to be related only to processing of relative magnitude. Experiment nos. 3 (bisection of an unfilled space) and 4 (bisection of flanked lines/unfilled spaces) aimed at disclosing perceptual, attentional, and numerical constraints on the bias induced by the position of the larger digit. This effect is interpreted in terms of a cognitive illusion of length, whereby a spatial bias compensates for the numerical disparity. This seems to operate in a categorical fashion ("small/large"), and to be congruent with the assumption that relatively large numbers are associated with the right side of a mental representational space.