Metaphor processing in autism: A systematic review and meta-analysis

Impairments related to figurative language understanding have been considered to be one of the diagnostic and defining features of autism. Metaphor comprehension and production in autism spectrum disorder (ASD) as compared to typically developing (TD) individuals have been investigated for around thirty years, generally showing an overall advantage for TD groups. We present a preregistered systematic review and meta-analysis including a total of 15 studies that fulfilled our set of inclusion criteria (notably, ASD and TD groups matched in chronological age and verbal- or full-scale IQ). Along with accuracy, we also analyzed group differences in reaction time in the studies that reported them. The results revealed a medium-to-large group difference favoring TD over ASD groups based on accuracy measures, as well as a similar overall advantage for TD groups based on reaction times. There was reliable heterogeneity in effect sizes for group differences in accuracy, which was mostly explained by the effect of verbal intelligence, with differences in metaphor processing being smaller for participants with better verbal skills. Some of the variation in effect sizes may also be attributed to differences in types of metaphor processing tasks. We also evaluated the quality of the studies included in the meta-analysis, and the evidence relating to the potential presence of publication bias.