Intact 'inner speech' use in autism spectrum disorder: evidence from a short-term memory task

Background: Inner speech has been linked to higher-order cognitive processes including 'theory of mind', self-awareness and executive functioning, all of which are impaired in autism spectrum disorder (ASD). Individuals with ASD, themselves, report a propensity for visual rather than verbal modes of thinking. This study explored the extent to which children with ASD used inner speech or visual imagery to support recall from short-term memory. Method: Twenty-five children with ASD and 20 comparison children with moderate learning disabilities completed an immediate serial recall task, in which stimuli consisted of items with either phonologically similar features, visuo-spatially similar features or control items which were neither visuo-spatially nor phonologically similar. Results: ASD and comparison participants, with verbal mental ages above 7 years, recalled phonologically similar stimuli less well than control stimuli, indicating that both groups were using inner speech to recode visually presented information into a phonological code. In contrast, those participants with verbal mental ages below 7 years, whether with ASD or not, recalled visuo-spatially similar stimuli less well than control stimuli, indicating visual rather than phonological coding. This developmental pattern mirrors that found in typically developing children. Conclusions: Under experimental conditions, individuals with ASD use inner speech to the same extent as individuals without ASD of a comparable mental age.