Decoding Numeracy and Literacy in the Human Brain: Insights from MEG and MVPA

Numbers and letters are the fundamental building blocks of our everyday social interactions. Previous studies have focused on determining the cortical networks shaped by numeracy and literacy in the human brain, partially supporting the hypothesis of distinct neural circuits involved the processing of the two categories. In this study, we aim to investigate the temporal dynamics for number and letter processing. We present MEG data from two experiments (N=20 each). In the first experiment, single numbers, letter, and their respective false fonts (false numbers and false letters) were presented, whereas, in the second experiment, numbers, letters, and their respective false fonts were presented as a string of characters. We used multivariate pattern analysis techniques (time-resolved decoding and temporal generalization) testing the strong hypothesis that the neural mechanisms supporting letter and number processing can be logistically classified as categorically separate. Our results show a very early dissociation ([~]100 ms) between numbers, and letters when compared to false fonts. Number processing can be dissociated with similar accuracy when presented as isolated items or strings of characters, while letter processing shows dissociable classification accuracy for single items compared to strings. These findings reinforce the evidence indicating that early visual processing can be differently shaped by the experience with numbers and letters; this dissociation is stronger for strings compared to single items, thus showing that combinatorial mechanisms for numbers and letters could be categorically distinguished and influence early brain activity.