An event-related brain potential study of the arithmetic split effect

This study explores the split effect on arithmetical sequence processing using event-related brain potentials (ERPs). This effect has been reported in arithmetic problem verification tasks and refers to an increase in reaction time when an incorrect solution close to the correct one is presented. The use of different strategies has been suggested to account for this effect: a whole-calculation strategy for close incorrect solutions (small-split problems), and a plausibility-checking strategy for far or obviously incorrect solutions (large-split problems). In the present study, participants were asked to verify whether the last item of a numerical sequence was correct or not, according to the rule established by the preceding numbers. Subjects were presented with sequences of numbers, and the distance between the proposed and the correct ending was manipulated by presenting the correct ending, a small-split ending or a large-split ending. To avoid problems that violated the parity rule only even numbers were presented. Two ERP components were evident whenever the arithmetical sequence was broken: an early negativity peaking at about 270 ms and a subsequent late positivity component (LPC) peaking between 550 and 650 ms. The early negativity was larger at posterior sites. The late positivity had a centro-parietal scalp distribution, and its amplitude was sensitive to the numerical distance from the correct number: the greater the distance, the larger the positivity. The present results suggest that the centro-parietal LPC can be taken as an index of the split effect and may broaden our knowledge about arithmetical processing strategies.