Some utterances are underinformative: The onset and time course of scalar inferences

When Tarzan asks Jane Do you like my friends? and Jane answers Some of them, her underinformative reply implicates Not all of them. This scalar inference arises when a less-than-maximally informative utterance implies the denial of a more informative proposition. Default Inference accounts (e.g., Levinson, 1983, 2000) argue that this inference is linked to lexical items (e.g., some) and is generated automatically and largely independently of context. Alternatively, Relevance theory (Sperber & Wilson, 1985/1995) treats such inferences as contextual and as arriving effortfully with deeper processing of utterances. We compare these accounts in four experiments that employ a sentence verification paradigm. We focus on underinformative sentences, such as Some elephants are mammals, because these are false with a scalar inference and true without it. Experiment 1 shows that participants are less accurate and take significantly longer to answer correctly when instructions call for a Some but not all interpretation rather than a Some and possibly all interpretation. Experiment 2, which modified the paradigm of Experiment 1 so that correct responses to both interpretations resulted in the same overt response, reports results that confirm those of the first Experiment. Experiment 3, which imposed no interpretations, reveals that those who employed a Some but not all reading to the underinformative items took longest to respond. Experiment 4 shows that the rate of scalar inferences increased as permitted response time did. These results argue against a Neo-Gricean account and in favor of Relevance theory. (C) 2004 Elsevier Inc. All rights reserved.