Left-to-right coding of number magnitudes: Inherent or not?

One of the issues of major interest in numerical cognition is the relationship between the brain representation of space and that of numerical magnitudes. Space–Number interactions have been vari- ously ascribed to the inherent spatial coding of number magnitudes, to the verbal coding of space determined by the use of contrasting left/ right spatial codes in the task at hand or to the use of the same spatial codes in the selection of motor responses associated with numerical features such as magnitude or parity. In my talk, I shall review the results gathered from behavioral, neuropsychological, electrophysio- logical and fMRI investigations run in our lab. Through the use of different behavioral paradigms like the mental bisection of number intervals, the SNARC and Attentional-SNARC tasks (both in their original and modified versions) we demonstrate that the use of spatial codes in the numerical task at hand is crucial in determining the Space–Number interaction when numerical information are recovered from LTM knowledge. This happens both when spatial codes are directly associated with number stimuli and when the same codes are indirectly associated with numbers through the selection of motor responses. These findings outdate the idea that numbers have an inherent spatial representation or that, vice-versa, the mere perception of numbers determines spatial orienting in the left or right side of space according to number magnitude. Critical comparisons with the results and hypotheses from other labs will be also provided and future lines of investigations will be sketched during the talk.