Differentiating challenge reactivity from psychomotor activity in studies of children’s psychophysiology: Considerations for theory and measurement

► Assessment of child “stress reactivity” may be confounded by psychomotor activity. ► “Non stressful” comparison tasks themselves elicited RSA and PEP responses. ► Reactivity adjusted for psychomotor activity was incongruent with traditional react. ► It is important to account for confounding psychomotor activity effects. ► Refinement of assessment of child physiologic reactivity may improve prediction. Current methods of assessing children’s physiological “stress reactivity” may be confounded by psychomotor activity, biasing estimates of the relation between reactivity and health. We examined the joint and independent contributions of psychomotor activity and challenge reactivity during a protocol for 5- and 6-year-old children ( N = 338). Measures of parasympathetic reactivity (respiratory sinus arrhythmia [RSA]) and sympathetic reactivity (preejection period [PEP]) were calculated for social, cognitive, sensory, and emotional challenge tasks. Reactivity was calculated relative to both resting and a paired comparison task that accounted for psychomotor activity effects during each challenge. Results indicated that comparison tasks themselves elicited RSA and PEP responses, and reactivity adjusted for psychomotor activity was incongruent with reactivity calculated using rest. Findings demonstrate the importance of accounting for confounding psychomotor activity effects on physiological reactivity.