Reaction time as a process indicator in digital symptom assessment

Background: Individuals with mild intellectual developmental disorder (IDD) and borderline intellectual functioning (BIF) often face challenges in self-reporting mental health symptoms. Reaction time (RT) may offer a dynamic process indicator to supplement static symptom reports. Objective: This study explored whether RT data collected during a digital, cognitively accessible self-report tool (iSpe®) could provide insights into cognitive and emotional processing during mental health assessment. Methods: Twenty-seven adults (neurotypical, BIF, and mild IDD) completed symptom-specific modules on an iPad, with item-level RT recorded. Linear regression analyses assessed RT trends across items. Outliers were identified within participants, and RT patterns were analyzed by cognitive functioning level. Results: Significant negative RT trends were observed across agoraphobia, panic anxiety, and insomnia domains, suggesting task habituation or reduced processing load. RT outliers were most frequent among BIF participants, indicating heterogeneity in cognitive engagement. Items eliciting frequent outliers often involved primary symptom content or functional consequences. Conclusion: RT captured dynamic cognitive-affective processes beyond static symptom responses, supporting its use as a sensitive, low-burden behavioral marker. Integrating RT into digital PROMs may enhance the validity, adaptability, and person-centeredness of mental health assessments for individuals with cognitive vulnerabilities