Mathematics is another domain, usually considered quite distinct from language, which has shown canonical N400 effects. Whether using an arithmetic verification task or a more implicit probe task (Galfano et al 2004), responses to incorrect (versus correct) solutions are characterized by centro-parietal negativity, which within-subjects comparisons indicate is virtually identical to that for semantically incongruous words in written sentences (Niedeggen et al 1999). Perhaps even more importantly, the arithmetic N400 effect shows a remarkable functional similarity to lexico-semantic ones: its amplitude is similarly sensitive to relations between items in long-term memory and is dissociable from concomitant RT measures. For example, Nieddegen and Roesler (1999) recorded ERPs and RTs for multiplication facts (5 × 8) that were either correct (40) or incorrect, and, when incorrect, varied in numerical distance from the correct product and were either related (32, 24, 16) or unrelated (34, 26, 18) to the operands. Both these factors influenced RTs, additively. N400s, however, were small to correct solutions, equally large to all unrelated solutions and to distant, related solutions, and intermediate in size to incorrect solutions that were
