New research has discovered that mood can change over time, and this has implications for how scientists conduct psychological experiments. The findings of the study, which was published in the journal Nature Human Behaviour, showed that participants’ moods gradually declined with time as they completed simple tasks or rest periods.
The study was conducted by a team of international researchers who intermixed subjective momentary mood ratings into repetitive psychology paradigms. The effect was called “mood drift over time” and was consistent across 19 cohorts, totalling 28,482 adult and adolescent participants.
The researchers found that the drift was relatively large, with participants experiencing a decline in the mood of 13.8% after 7.3 minutes of rest. This effect was consistent across all cohorts, and impacted behaviour as well; participants were less likely to gamble in a task that followed a rest period.
Interestingly, the drift slope was inversely related to reward sensitivity, suggesting that participants who were less sensitive to rewards were more likely to experience mood drift over time.
The findings have important implications for how scientists conduct psychological experiments. For example, in a resting-state functional brain scan, comparisons of resting-state neuroimaging data between depressed and non-depressed participants are thought to reveal differences in their task-general traits. However, this assumption of a constant affective background may be flawed.
The researchers suggest that accounting for time using a linear term significantly improves the fit of a computational model of mood. They argue that their work provides conceptual and methodological reasons for researchers to account for time’s effects when studying mood and behaviour.
The mechanism that enables mood to be sensitive to the passage of time is not yet known. One possibility is that humans store expectations about the rate of rewards and punishments in the environment and that prolonged periods of monotony violate such expectations. Lower mood could function as an estimate of that opportunity cost, making mood drift an adaptive signal that informs decisions to exploit (stay on task) or explore (switch task).
Overall, the study provides robust empirical evidence for the phenomenon of Mood Drift Over Time and calls into question the long-held constant affective background assumption in behavioural and affective science.
The researchers state that the constant affective background assumption has profound methodological implications for psychological experiments. For example, in an event-related design, such as a gambling or face recognition task, during which participants experience stimuli (wins or losses) that elicit emotional reactions, responses to task stimuli are thought to occur on top of (and are often contrasted to) the affective baseline, which is presumed to be time-invariant. However, the findings of this study suggest that mood can change over time, and therefore, should be accounted for when conducting such experiments.
The researchers argue that the assumption of a constant affective background has implications for clinical studies, as it could affect the interpretation of data from resting-state functional brain scans. The researchers suggest that accounting for mood drift over time could help to better understand differences in the resting-state brain activity of depressed and non-depressed participants.
The study has also provided insight into the mechanism of mood drift over time. The researchers suggest that the effect could be due to the violation of expectations about the rate of rewards and punishments in the environment. Lower mood could function as an estimate of that opportunity cost, making mood drift an adaptive signal that informs decisions to exploit (stay on task) or explore (switch task).
The findings provide robust empirical evidence for the phenomenon of mood drift over time and have important implications for how scientists conduct psychological experiments. The findings suggest that researchers should account for time’s effects when studying mood and behaviour and that the constant affective background assumption should be questioned. Furthermore, the study provides insight into the mechanism of mood drift over time, which could have implications for understanding the cognitive processes that underlie human decision-making and task performance.