Objectives: To investigate whether high-functioning adults with autism are capable of deriving scalar implicatures, which are generally considered as pragmatic inferences.
Methods: We carried out a behavioral experiment on high-functioning adults with autistic disorder (n=11) or Asperger syndrome (n=18) and matched controls (n=28). Participants were presented with underinformative sentences like “Some sparrows are birds” and “Zebras have black or white stripes”. These sentences are logically true, but pragmatically infelicitous if the scalar implicatures “Some but not all sparrows are birds” and “Zebras have black or white stripes but not both” are derived. The task was to judge whether the presented sentences were true or false. Responses and reading times were measured.
Results: Participants with autistic disorder derived fewer scalar implicatures than participants with Asperger syndrome, but they did not differ in response pattern from the control group. However, reading time data suggest that the autistic disorder group needed more time to perform the task. In contrast, participants with Asperger syndrome performed at normal levels and even better. Moreover, in the autistic disorder group the number of derived implicatures correlated with verbal intelligence. In the Asperger syndrome and group control group no such correlations were found.
Conclusions: Our findings indicate that a differentiation between high-functioning autistic disorder and Asperger syndrome is relevant. Moreover, our results suggest that verbal intelligence is a constraint on task performance in autism.