Daily life fluctuations in affect predict within-person changes in a real-world measure of cognitive processing speed

Considerable research points to a deleterious effect of negative affect on cognition. However, most evidence comes from experimental induction paradigms with unclear implications for cognitive performance in the real world. Here, we developed a microlongitudinal design to examine the between- and within-person (contemporaneous and time-lagged) relationships between affect and cognitive processing speed. Across three separate ecological momentary assessment datasets, a total of 914 participants (70.89% female) between 18 and 82 years tracked negative and positive affect 2 or 3 times daily, for 6 or 8 weeks, completing between 63 and 126 assessments each. Cognitive processing speed was measured using a recently validated method derived from time to respond to surveys (digital questionnaire response time, DQRT). Data were analyzed using multilevel vector autoregressive models. Affect and DQRT were related between-person; people with higher average negative affect were slower in responding to survey items overall, with the opposite for positive affect. This was observed for 36/37 affective items assessed. At the within-person level, DQRT was slower when negative affect increased and positive affect decreased for 34/37 items. In lagged analyses, higher negative affect (and lower positive affect) predicted slower DQRT at the next time point (5 to 12 hours later) for 27/37 items. The strongest predictors of future DQRT were feeling worried and anxious, and there was no evidence for reverse temporal causation. In conclusion, we identified a potential causal relationship where negative affect predicts slower survey completion times. This finding may inform mechanistic accounts of cognitive deficits in mental health disorders.