Defeasible inference in autism: a behavioral and electrophysiological approach

Although people with autism spectrum disorders (ASD) often have severe problems with pragmatic aspects of language, little is known about their pragmatic reasoning. We carried out a behavioral study on high-functioning adults with autistic disorder (n = ii) , with Asperger syndrome (n=!7), and matched controls (n=28) to investigate whether they are capable of deriving scalar implicatures, which are generally consid­ ered to be pragmatic inferences. Participants were presented with underinformative sentences like “ Some sparrows are birds” . This sentence is logically true, but pragmatically inappropriate if the scalar implicature “ Not all sparrows are birds” is derived.The present findings indicate that the combined ASD group was just as likely as controls to derive scalar implicatures, yet there was a difference between partici­ pants with autistic disorder and Asperger syndrome, suggesting a potential differenti­ ation between these disorders in pragmatic reasoning. Moreover, our results suggest that verbal intelligence is a constraint for task performance in autistic disorder but not in Asperger syndrome. This chapter has been based on: Pijnacker, J., Hagoort, P., Buitelaar, J.K.,Teunisse, J-P, Geurts, B. (2009). Pragmatic inferences in high-functioning adults with autism and Asperger syndrome, Journal of autism and developmental disorders 39 (4), 607-618. P ra g m a tic in fe ren ces in A S D : sca lar im p lic a tu re s 23 Introduction In everyday discourse, the meaning of an utterance usually goes beyond its explicit linguistic meaning. For example, consider the following dialogue: a. A: Would you like some chicken soup? b. B: I am a vegetarian. B's answer seems irrelevant, unless a pragmatic inference is made. In order to under­ stand her reply, one must infer that vegetarians do not eat chicken, and therefore she does not want to have chicken soup. This inference is a pragmatic one, because it is not entailed by the literal content of B's utterance. Over the past decades, research on autism spectrum disorders (ASD) has shown that pragmatic impairments are widespread in ASD. Pragmatic impairments are found in both children and adults with autistic disorder and Asperger syndrome, whereas formal language deficits (i.e. deficits in syntax, semantics, phonology) are not defin­ ing features of ASD (DSM-IV, 1994) and show a wide variability among persons with ASD (Kjelgaard & Tager-Flusberg, 200!; Tager-Flusberg, 2006). In this paper, we focus on high-functioning ASD, that is, ASD without intellectual disability, usually defined as having an intelligence of 85 or above. Research indicates that high-functioning people with ASD usually have relatively intact core language features (Minshew, Goldstein, & Siegel, 1995), although others suggest mild to moderate impairments (see also over­ views by Boucher, 2003; Walenski, Tager-Flusberg, & Ullman, 2006). What is univer­ sal in ASD are severe problems with pragmatic aspects of language (Baron-Cohen, 1988; Boucher, 2003; Eales, 1993; Martin & McDonald, 2003; Ozonoff & Miller, 1996; Tager-Flusberg, 1981, 1996) as is shown, for example, by inappropriate turn-taking in conversations, abnormal prosody, inability to adjust to the communicative setting (e.g. impoliteness, embarrassing questions, pedantic speech), and difficulties in differ­ entiating between old and new information. Furthermore, difficulties in understand­ ing non-literal language have been observed. People with ASD tend to interpret irony and metaphors literally and have difficulty understanding humor (Dennis, Lazenby, & Lockyer, 200!; Emerich, Creaghead, Grether, Murray, & Grasha, 2003; Happé, 1993, 1995; Martin & McDonald, 2004). Despite the considerable amount of literature on pragmatics in ASD, there is a paucity of research on pragmatic reasoning, that is, the ability to make inferences that go beyond the linguistic meaning of utterances. Studies that have examined prag­ matic inferences in ASD have focused on bridging inferences and global inferences required for text interpretation (Dennis et al., 200!; Jolliffe & Baron-Cohen, 1999, 2000). People with ASD were found to be less able to use contextual information to make a global inference in a sentence arrangement task, and were less likely to