The brain goes the distance: a shared numerical magnitude representation revealed by a frequency-tagging multi-code EEG study

Humans can effortlessly abstract numerical information from various formats, codes, and contexts. However, whether the access to the underlying magnitude information relies on common or distinct brain representations remains highly debated. Here, we recorded electrophysiological (EEG) responses to periodic variation of numerosity (every five items) occurring in rapid streams of numbers presented at 6Hz in randomly varying codes – Arabic digits, number words, canonical dot patterns and finger configurations – thus mixing symbolic and iconic formats. Results demonstrated that numerical information was abstracted and generalized over the different representation codes by revealing clear discrimination responses (at 1.2 Hz) of the deviant numerosity from the base numerosity (both presented in various codes), recorded over parieto-occipital electrodes. Crucially, and supporting the claim that discrimination responses reflected magnitude processing, the presentation of a deviant numerosity distant from the base (e.g., base “2” and deviant “8”) elicited larger right-hemispheric responses than the presentation of a close deviant numerosity (e.g., base “2” and deviant “3”). This finding nicely represents the neural signature of the so-called distance effect, an interpretation further reinforced by the clear correlation with individuals’ behavioral performance in an independent numerical comparison task. Our results therefore provide for the first time unambiguously a reliable and specific neural marker of a magnitude representation that is shared among several numerical formats