When people are more logical under cognitive load: dual task impact on scalar implicature

The present study introduces dual task methodology to test opposing psychological processing predictions concerning the nature of implicatures in pragmatic theories. Implicatures routinely arise in human communication when hearers interpret utterances pragmatically and go beyond the logical meaning of the terms. The neo-Gricean view (e.g., Levinson, 2000) assumes that implicatures are generated automatically whereas relevance theory (Sperber & Wilson, 1986/1995) assumes that implicatures are effortful and not automatic. Participants were presented a sentence verification task with underinformative sentences that have the potential to produce scalar implicatures like Some oaks are trees. Depending on the nature of the interpretation of Some (logical or pragmatic) the sentence is judged true or false. Executive cognitive resources were experimentally burdened by the concurrent memorization of complex dot patterns during the interpretation process. Results showed that participants made more logical and fewer pragmatic interpretations under load. Findings provide direct support for the relevance theory view.