Finding a Face in the Crowd: Developmental Change of Sensitivity to Threatening Faces in Children with Autism Spectrum Disorders

Background:  An atypical face and emotion processing in individuals with autism spectrum disorders (ASD) have received wide attention in the research of cognitive characteristics in ASD.  Although many studies have tackled on this issue, it is still not clear whether / how their processing is different from typical people.  In the current study, we focused on the "anger superiority effect". This effect refers a phenomenon where an angry face is detected more quickly than a happy or neutral face in a crowd of distracter. This is believed to be brought by the attention-getting properties in such threatening stimuli. Previous studies reported that individuals with ASD showed the quick anger detection ability as typically developed people did (Ashwin et al., 2006; Krysko & Rutherford, 2009).  Interestingly, however, individuals with ASD showed weaker effect than the typical people at a larger crowd size. These previous findings raised a question, whether the rapid processing to the threat in adults with ASD is brought by the same mechanism as typical people use, or they use a different strategy to compensate their poorer emotion perception. In the latter case, the rapid processing to the threat in ASD can be considered to be acquired through their development. To address the question, we tested the angry superiority effect in children with and without ASD.

Objectives:  In this study, we aimed to test the anger superiority effect in children with and without ASD, and to examine the developmental change in this effect.

Methods:  19 children with ASD ages 7 to 11 years old and 18 typically developing children (TD) with same age participated in this study.  Visual search paradigm using touch-sensitive monitor was employed.  Schematic facial stimuli including angry, happy, and neutral faces were used.  The task includes two conditions to examine the search asymmetry effect.  In the first condition, emotional faces were presented as targets and neutral faces were presented as distracters.  In the other condition, neutral faces were presented as targets and emotional faces were presented as distracters.  Participants were required to touch the object which is different from others as quick as possible.  Reaction times in correct responses were measured.  

Results:  The results revealed that an angry face was detected more quickly than a happy face both in ASD and in TD.  However, when integrating the effect of emotional stimuli both as a target and as distracters (Emotion Effect Index: EEI), which indicates the size of search asymmetry effect, the EEI was significantly different between the groups. Further analysis revealed that the EEI tended to be predicted by age in ASD, but not in TD.  

Conclusions: These results suggested that children with ASD may acquire the sensitivity to the threat in faces as they grow up.