Intraindividual reaction time variability, respiratory sinus arrhythmia, and children's externalizing problems.

Intraindividual reaction time variability (IIRTV) is a unique cognitive function index that is independent of accuracy and has been found to be related to children's externalizing problems. Respiratory sinus arrhythmia (RSA) reactivity to challenge tasks was also found to be a potential influence factor of children's externalizing problems. The present study examined whether IIRTV interacts with RSA reactivity to relate to externalizing problems in children. The flanker task was administered to 168 early elementary school-age children to assess their IIRTV, and the Child Behavior Checklist-Chinese version (CBCL-CV) was completed by their parents to assess children's externalizing problems. Electrocardiogram data were collected during the resting and task period to calculate resting RSA and RSA reactivity. The results indicated that children's IIRTV was correlated with their externalizing problems. Importantly, IIRTV interacted with RSA reactivity to relate to externalizing problems. IIRTV was positively related to externalizing problems in children with RSA suppression but was not significantly related to externalizing problems in children with RSA augmentation during the task. These findings suggest that poor attentional or cognitive control, as indexed by greater IIRTV, is related to more externalizing problems. Moreover, during mild cognitive stress, greater RSA suppression might indicate poor physiological regulation, which is more likely to increase externalizing problems for children with poor attentional or cognitive control.