P600 related to rule violation in an arithmetic task.

The goal of the present paper was to study if a similar neurophysiological process is required for treating violations of both arithmetical rules and linguistic syntactic structures. It has been shown that syntactic violations elicit the P600/syntactic positive shift (SPS) component, reflecting secondary parsing processes or repairing of an incorrect syntactic structure. However, late positivities, similar to the P600/SPS component, are also elicited by other types of violations (e.g. harmonic anomalies or violations in non-linguistic abstract rules), so this component is thought to be an index of detection for any anomaly in rule-governed sequences. We carried out an experiment where violations of arithmetic rules were presented. These violations were evident to a greater or lesser degree (a number very different or very similar to that which correctly completed a series of seven numbers). The type of rule was also manipulated, and increasing and decreasing series were presented. Results showed a late centro-parietal positivity related to arithmetic violations, whose amplitude was larger, the more evident the violation presented was, in both addition and subtraction. It is concluded that a similar neurophysiological process could be required for the processing of violations in numerical sequences and in linguistic syntactic structures. When the rule was broken, another component was present for the adding operation: an early negativity peaking between 250- and 300-ms post-stimulus. Regarding this negative peak, although some possible explanations are drawn, further research needs to be carried out in order to gather more knowledge about it.