In two experiments we evaluated the coactivation of arithmetic facts and the possible inhibitory mechanism used to select the correct one. To this end, we introduced an adapted version of the negative priming paradigm in which participants received additions and they decided whether they were correct or not. When the addition was incorrect but the result was that of multiplying the operands (e.g., 2 + 4 = 8), participants took more time to respond relative to control additions with unrelated results. This finding corroborated that participants coactivated arithmetic facts of multiplications even when they were irrelevant to perform the task. Moreover, the participants were slower to respond to an addition whose result was that of multiplying the operands of the previous trial (e.g., 2 + 6 = 8). These results support the existence of an inhibitory mechanism involved in the selection of arithmetic facts.

This study aimed at exploring the time course of processes underlying the associative confusion effect. We also evaluated the consequences of selecting arithmetic facts to resolve addition problems. We gathered electrophysiological evidence when participants performed a verification task. Simple addition problems were presented in blocks of two trials and participants decided whether they were correct or not. The N400-like component was considered an index of semantic access (i.e., the retrieval of arithmetic facts), and the P200 component was used to determine the difficulty associated with encoding after the answer to an addition problem. When an addition problem was incorrect but the result presented to the participant was that of multiplying the operands (e.g., 2 + 4 = 8), N400-like amplitude was reduced relative to an unrelated condition (e.g., 2 + 4 = 10). This finding suggested that the coactivation of addition and multiplication facts took place. Furthermore, the P200 amplitude was more positive when participants answered to addition problems whose result was that of multiplying the operands of the previous trial (e.g., 2 + 6 = 8). This suggests that irrelevant results were inhibited and it was difficult to encode them later.

We examined the role of numerical format in the activation and selection of arithmetic facts. We also explored the inhibitory nature of this mechanism. To this end, in two experiments we manipulated the format of the operations (digit format and word format) while participants decided whether simple additions were correct or not. In Experiment 1, when an addition was incorrect but the result was that of multiplying the operands (e.g., 2 + 4 = 8), participants took more time to respond relative to a control condition where the addition's result was incorrect but unrelated. Afterward, participants took more time to respond when the result of multiplying the operands was presented again in a correct addition problem (e.g., 2 + 6 = 8), suggesting that the related multiplication result in the previous trial (e.g., 8) was inhibited to select the correct response (e.g., 6); thus, when it was presented again in the next problem, additional time was necessary to reactivate it. These effects were found in the digit format but not in the word format. In Experiment 2, we considered the degree to which participants used memory retrieval to perform the task. In participants with high retrieval usage, the interference effects in the first and second trials were larger for the digit format than for the word format. However, the participants with low retrieval usage showed interference effects only for problems with digits. These findings are discussed in terms of automaticity in retrieving arithmetic facts to perform simple arithmetic.

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