Humans dedicate a significant portion of their time to intrinsically rewarding activities—those enjoyable in their own right, irrespective of external outcomes. Examples range from appreciating art and reading to solving puzzles and exploring nature. Unlike activities driven by primary rewards (e.g., eating, procreation) with clear survival benefits, or secondary rewards (e.g., money) linked to primary rewards, the common underlying features of intrinsic rewards remain less understood. This study investigates the hypothesis that despite their apparent diversity, sensitivity to intrinsic rewards shares core characteristics and is partially domain-general, potentially overlapping with sensitivity to secondary rewards. Engagement with specific intrinsically rewarding stimuli has been linked to happiness, mental health, and professional success. This study posits that these findings stem from a core relationship between mental health and domain-general sensitivity to intrinsic rewards. Individuals highly sensitive to intrinsic rewards are predisposed to engage in a variety of such activities, increasing their chances of discovering pursuits they excel at. Conversely, low sensitivity might lead to disinterest in diverse activities, potentially resulting in low mood and lack of motivation. Therefore, domain-general sensitivity to intrinsic rewards could contribute significantly to flourishing, while its absence might contribute to suffering. This research focuses on affective health, encompassing characteristics like positive mood, high motivation, feelings of pleasure, interest, and happiness. By examining responses to visual, cognitive, and social intrinsic rewards alongside monetary rewards and neutral stimuli, the study aims to determine if within-individual responses to intrinsic rewards are domain-general and linked to affective mental health.

Prior research has explored the association between engagement with specific intrinsically rewarding stimuli and various positive outcomes such as happiness, mental health, and professional achievement. However, this study seeks to move beyond these isolated observations by exploring whether the observed associations might be explained by a more fundamental relationship between mental health and a domain-general sensitivity to intrinsic rewards. The authors hypothesize that a core aspect of this relationship may be captured by what they define as "affective health", and they plan to measure this with a range of questionnaires examining aspects such as mood, motivation, pleasure and interest. The literature on the link between mental health and reward sensitivity, particularly monetary reward sensitivity has provided mixed results, prompting the investigation into whether the processing of intrinsic rewards is more crucial for well-being.

The study employed three online experiments (Experiment 1, N=132; Experiment 2, N=171; Experiment 3, N=180). Each experiment measured liking, wanting, and reinforcing strength for various stimuli. Stimuli included three types of putative intrinsic rewards (visual, cognitive, social), their corresponding non-rewarding alternatives, a monetary reward (earning bonus money), its alternative (not receiving a bonus), and neutral stimuli (vertical and horizontal lines). Visual rewards were landscape images contrasted with wall images; cognitive rewards were informative sentences versus scrambled letter strings; social rewards involved learning about agreement versus disagreement with another participant's preferences; and the monetary reward was a picture of a coin representing a bonus payment. Liking was measured by rating how much participants liked each stimulus block. Wanting was measured differently across experiments. In Experiments 1 and 2, participants rated their preference for ten trials of a reward versus its alternative; in Experiment 3, they chose between the reward and alternative on each of 15 trials. Reinforcing strength was assessed by a probabilistic instrumental learning task where participants chose between cues probabilistically associated with the reward or its alternative. Data were analyzed using factor analysis with bi-factor rotation to determine if a general factor (reward sensitivity) explained variance across all reward types but not neutral stimuli. Affective health was assessed using multiple questionnaires, and a similar factor analysis was performed to derive a mental health score. Linear models examined the relationship between reward sensitivity and mental health score, controlling for demographics and IQ. Separate analyses examined the contribution of intrinsic versus monetary reward sensitivity to mental health.

The results demonstrated that intrinsic rewards, similar to monetary rewards, elicited liking, wanting, and reinforcement responses, unlike neutral stimuli. Factor analysis revealed a general factor, termed "reward sensitivity," accounting for approximately 40% of the variance in responses across all reward types (excluding neutral stimuli). This suggests a domain-general sensitivity to rewards. Crucially, reward sensitivity, particularly sensitivity to intrinsic rewards, was significantly associated with affective aspects of mental health. Linear regression models showed that intrinsic reward sensitivity predicted mental health scores even after controlling for demographics and IQ, whereas monetary reward sensitivity did not. The models using intrinsic reward sensitivity as the predictor also showed better model fit (lower BIC scores) compared to models using monetary reward sensitivity. Further analyses comparing intrinsic reward pairs versus pairs including monetary rewards also confirmed the stronger association between intrinsic reward sensitivity and mental health scores (lower summed BIC for models with only intrinsic rewards).

The findings support the hypothesis that sensitivity to diverse intrinsic rewards is domain-general and significantly related to affective mental health. The common sensitivity across intrinsic rewards, unlike monetary rewards, was strongly associated with better mental health scores. This suggests that the processing of intrinsic rewards may be more vital for well-being than previously appreciated, highlighting the need to study rewards beyond primary and secondary types. Potential common features underlying the rewarding nature of diverse intrinsic stimuli include self-efficacy (autonomy and competence) and curiosity (desire for information). These features might promote mental well-being, but further research is needed to elucidate the directionality and potential mediating factors in this relationship. The results also suggest potential shared neural underpinnings for intrinsic and other reward types, with the possibility of distinct neural mechanisms for distinguishing between different types of rewards and their values.

This study demonstrates that sensitivity to intrinsic rewards is partially domain-general and strongly linked to affective mental health, independent of monetary reward sensitivity. This highlights the significance of studying intrinsic rewards for understanding human well-being and suggests potential shared neural mechanisms and common features such as self-efficacy and curiosity that contribute to this association. Further research should investigate the causal relationships and neural correlates of this association, examining a wider range of intrinsic and primary rewards to confirm generalizability.

The fixed order of measurements in Experiments 1 and 2 is a limitation, although Experiment 3 addressed this by randomizing the order and replicated the key findings. The use of rating scales for both liking and wanting in Experiments 1 and 2 could have affected the correlation between these measures. Experiment 3 employed a choice task for wanting, mitigating this issue. The study focuses on correlations, not causations, limiting the ability to infer whether intrinsic reward sensitivity influences mental health or vice versa. Finally, the scope of intrinsic rewards is limited in this study, future research should expand to a wider range of rewards to evaluate the generalizability of the findings.