In the digital era, smartphone usage is shifting from functional utility to problematic engagement. Problematic smartphone use (PSU) is a construct defined as excessive smartphone use accompanied by functional impairments in daily life and symptoms resembling those of substance use disorders, with its core criterion being functional impairment—distinguishing it from “excessive use,” which involves no adverse consequences (Billieux et al., 2015). PSU falls within the scope of addiction research. While some researchers employ terms such as “smartphone addiction” (Kwon et al., 2013, Kuem et al., 2021, Li et al., 2024), Panova and Carbonell (2018) note that “PSU” more precisely defines this specific behavioral addiction phenomenon characterized by functional impairment. PSU avoids the overgeneralization of terminology that might obscure its specific characteristics. According to Lu et al. (2024), PSU is estimated to affect 37.1 % of adolescents globally, though prevalence varies across studies due to differences in assessment tools and cultural contexts. For example, 29.4 % of Chinese college students are at high risk of PSU (Hong et al., 2022), whereas PSU prevalence among U.S. adults is only 0.75 %–1.2 % (Rochat et al., 2025). Notably, such estimates rely primarily on self-reported data, which may be prone to response biases, limiting their reliability. Across cultures, PSU correlates with sleep impairment and academic decline (Tu et al., 2023).

Expectancy-Value Theory (Eccles & Wigfield, 2002) suggests that value expectations drive rational decision-making, yet smartphone use presents a potential paradox: initially rewarding behaviors may often develop into PSU due to failed self-regulation, manifesting as compulsive use and withdrawal distress (Busch and McCarthy, 2021, Elhai et al., 2017).

Reinforcer Pathology Theory proposes an explanation for this through distorted valuation, suggesting that immediate rewards (e.g., social media use) may be overvalued while the expected value of alternative behaviors (EVAB; e.g., psychological rewards from social or physical activities) may be undervalued (Acuff et al., 2023). Although enhancing the EVAB has been identified as a potential core mechanism in reducing behavioral addictions, which may include diminishing compulsive engagement in addictive behaviors by strengthening valuation of adaptive alternatives (Acuff et al., 2023, Field et al., 2020), its role in PSU remains unclear in two key aspects. First, existing research has primarily focused on value drivers within addictive behaviors themselves, such as the immediate hedonic rewards of smartphone use (e.g., likes and notifications; Allcott et al., 2022), or the impairing effect of immediate rewards on self-control in sexual addiction and cocaine addiction (Graczyk et al., 2023, Liberg et al., 2022). However, it has not yet fully explored the real-time associations between EVAB and PSU. Second, traditional methods cannot capture diurnal EVAB fluctuations or reveal momentary decision mechanisms. Using Ecological Momentary Assessment (EMA) with daily randomized sampling, this study examines dynamic EVAB-PSU relationships and mediating mechanisms. The findings may advance Reinforcer Pathology Theory with digital behavior evidence and inform real-time intervention development.

Within the context of behavioral addiction, the Expected Value of Alternative Behaviors (EVAB)—defined as an individual’s subjective appraisal of the benefits (e.g., pleasure, goal fulfillment) versus costs (e.g., time, effort) of engaging in non-addictive activities (e.g., social interactions, academic work)—is a critical yet understudied construct (Acuff et al., 2023). Expectancy-Value Theory (Eccles & Wigfield, 2002) delineates behavioral valuation as encompassing four dimensions: intrinsic motivation (inherent enjoyment), utility (goal relevance), social identity (self-concept alignment), and cost assessment (resource expenditure). Positive value expectations toward alternative behaviors enhance rational decision-making across domains, from consumer behavior (Kim et al., 2022) to academic achievement (Hidi, 2016).

For problematic behaviors such as PSU, the development of addiction may occur not only when addictive behaviors are overvalued but also when adaptive alternative behaviors are undervalued (Bickel et al., 2023). Specifically, PSU may persist when individuals fail to recognize or prioritize the value of alternative activities that can meet their psychological needs (e.g., social connection, achievement) without causing functional impairment (Kuem et al., 2021). Thus, EVAB may serve as a potential protective factor against PSU.

Reinforcer Pathology Theory directly articulates the influence of EVAB on addiction. This theory posits that imbalanced value allocation is a driving factor of addiction. When disproportionately concentrated on immediate-hedonic rewards, expected value amplifies addictive craving through dual mechanisms. These include the overvaluation of addictive behaviors (e.g., substance use) and the devaluation of alternative behaviors (e.g., exercise) (Acuff et al., 2023). Addictive behaviors deliver transient yet intense rewards, creating inflated value expectations that eclipse EVAB's long-term benefits (Hogarth, 2020). This pathological valuation may sustain compulsive drug-seeking despite adverse consequences.

Research from a cognitive function perspective has linked addictive behaviors to deficits in evaluating future rewards and self-regulatory mechanisms (Büchel et al., 2017; Krönke et al., 2020). For instance, in adolescents, heightened sensitivity to immediate rewards coupled with weakened self-control predicts the escalation of substance use (Graczyk et al., 2023). Similar cognitive biases—overvaluing immediate digital stimulation and undervaluing goal-directed behaviors—have been proposed as potential psychological underpinnings of PSU, a prototypical behavioral addiction(Kuem et al., 2021). Notably, individuals with stronger future orientation exhibit enhanced cognitive control over PSU (Li et al., 2024). However, how EVAB, a key protective factor against addiction, influence the fluctuation of problematic use patterns remains insufficiently explored.

Delay discounting is defined as the tendency to devalue future rewards relative to immediate ones (Amlung et al., 2019) and has been proposed as a critical mediator in the relationship between the EVAB and PSU. This construct reflects core deficits in self-regulation, where higher discount rates indicate greater impulsivity and a prioritization of immediate gratification over larger delayed outcomes (Bickel et al., 2014). Consistent with addiction research frameworks, elevated delay discounting has been strongly linked to both substance use disorders and behavioral addictions, including PSU (Cheng et al., 2021, Pancani et al., 2023). For example, individuals with high delay discounting rates exhibit heightened sensitivity to the immediate hedonic rewards of smartphone use (e.g., social notifications, entertainment content) while undervaluing its long-term costs (e.g., reduced productivity or social isolation) (Billieux et al., 2015, Busch and McCarthy, 2021, Sohn et al., 2019).

The core psychological mechanism underlying the association between EVAB and delay discounting likely stems from the inhibition of immediate impulses and the strengthening of future-oriented cognition. EVAB enhances individuals' ability to maintain attention on goal-relevant stimuli while inhibiting prepotent responses to immediate rewards (Piray et al., 2016). Neuroimaging studies have shown that individuals with stronger EVAB exhibit increased activation in the prefrontal cortex—particularly the dorsolateral prefrontal cortex (DLPFC)—during delayed reward tasks, a brain region critical for evaluating future outcomes and inhibiting impulsive choices (Tabara et al., 2024). Enhanced EVAB may improve future-oriented valuation processes, reducing the subjective devaluation of delayed rewards characteristic of high delay discounting. For instance, Benningfield et al. (2014) found through a monetary incentive delay task that young adults exhibited lower delay discounting rates when anticipating delayed rewards compared to immediate ones.

In the context of PSU, this mechanism may follow a specific pathway: stronger EVAB may reduce delay discounting by enhancing cognitive control over immediate reward impulses and increasing emphasis on delayed benefits (e.g., academic achievement, interpersonal relationships). Conversely, weakened EVAB may impair these regulatory processes, increase delay discounting and thereby amplify susceptibility to the immediate rewards of PSU (Krönke et al., 2020). Empirical support for this chain comes from addiction research: Sofis et al. (2020) significantly reduced delay discounting rates and cannabis use frequency by guiding cannabis users to anticipate future alternative behaviors (e.g., marriage); Stein et al. (2018) instructed tobacco addicts to anticipate smoking-unrelated events and found significant reductions in both delay discounting levels and tobacco craving. Notably, while these studies did not directly measure the EVAB levels of anticipated events, their results indirectly support the mechanism that “anticipatory processing of alternative behaviors can reduce delay discounting.” Additionally, research has shown that reduced delay discounting is associated with decreased PSU severity (Hayashi, 2024, Pancani et al., 2023). However, the direct mediating role of delay discounting in the relationship between EVAB and PSU remains empirically untested, representing a critical gap in current research.

In the serial mediation model, Episodic Future Thinking (EFT) may function as a key antecedent mechanism that influences PSU through sequential pathways of enhancing the EVAB and reducing delay discounting. EFT refers to the capacity to mentally simulate or imagine personal future experiences by projecting oneself into hypothetical scenarios based on current or past contexts (Atance & O'Neill, 2001). This capacity varies across individuals and may exert cross-level effects: higher EFT capacity predicts stronger daily EVAB levels, lower degrees of delay discounting, and less severe PSU.

Empirical studies have demonstrated that EFT interventions modify behavioral outcomes through these mediating pathways. Guided positive EFT interventions—such as envisioning future travel scenarios or health benefits of abstinence—reduce alcohol and tobacco consumption (Voss et al., 2022), alleviate drug cravings (Moustafa et al., 2018), and mitigate internet addiction (Li, 2021). These effects are attributed to changes in EVAB and delay discounting. Specifically, EFT enhances EVAB by strengthening the perceived likelihood of future goal attainment (Ernst & D’Argembeau, 2017) and fostering positive affective experiences tied to future goals (Hallford et al., 2020, Wang et al., 2022). Meanwhile, it reduces delay discounting by promoting goal-directed cognition, which diminishes impulsive preferences for immediate rewards (Burns et al., 2022, Chang and Ladd, 2023, Mellis et al., 2019, Sze et al., 2017, Wang et al., 2022). Consistent with Expectancy-Value Theory (Eccles and Wigfield, 2002, Schacter et al., 2017) and Reinforcer Pathology Theory (Acuff et al., 2023), EFT restores the balanced valuation of future versus immediate rewards, thereby reducing addictive behaviors—a logic that suggests EFT may influence PSU through the serial mediating role of EVAB and delay discounting.

Notably, the three core dimensions of EFT—detail/vividness, clarity of mental imagery, and emotional valence—may exert differential effects on these mediating processes (Miloyan & McFarlane, 2019). Detail/vividness (the richness of contextual and sensory details in future simulations) enhances EVAB by making future outcomes more concrete and credible, as specific representations of future goals strengthen their perceived attainability (D'Argembeau & Mathy, 2011). Clarity of mental imagery (the sharpness and coherence of simulated scenarios) primarily influences delay discounting by enhancing the salience of long-term goals, enabling individuals to maintain focus on future rewards rather than succumbing to immediate gratification (Lin & Epstein, 2014). Emotional valence (the positive or negative affect embedded in future simulations) amplifies both pathways: positive valence increases the hedonic value of future-oriented behaviors (enhancing EVAB) and reduces the emotional drive for impulsive immediate rewards (lowering delay discounting), whereas negative valence may weaken these effects or even exacerbate the discounting of delayed outcomes (Chang & Ladd, 2023).

Despite these theoretical linkages, empirical evidence remains scarce regarding whether individual differences in specific dimensions of EFT are associated with daily fluctuations in EVAB, delay discounting, and PSU severity. This highlights a critical gap that needs to be addressed.

Traditional cross-sectional or longitudinal studies struggle to capture within-person fluctuations in EVAB, delay discounting, and PSU or assess how between-person differences in EFT influence daily dynamics. To address this, we used EMA and Dynamic Structural Equation Modeling (DSEM). EMA reduces recall bias and enhances ecological validity by measuring EVAB, delay discounting, and PSU in naturalistic settings (Myin-Germeys et al., 2018, McNeish and Hamaker, 2020), while DSEM disentangles within-person and between-person effects. Participants completed assessments three times daily for 14 consecutive days (time interval: 5 h). DSEM examines (1) the within-person relationship between EVAB and PSU mediated by delay discounting, and (2) whether between-person EFT levels are associated with these within-person processes. In this study, participants were assessed three times daily over 14 consecutive days, with an average interval of five hours between measurements. To ensure the robustness of the study findings, we have controlled for key covariates that may confound the relationships between EVAB, delay discounting, and PSU. These covariates include: (1) demographic variables (age, gender); (2) anxiety and depression status. Previous studies have shown that age, gender, anxiety, and depression status are all associated with PSU or delay discounting (Horwood et al., 2021, Huang et al., 2021, Lu et al., 2023). Using DSEM, this study aims to clarify the complex relationships by dissecting between- and within-person effects in EMA data Fig. 1. The study tests the following hypotheses:

Hypothesis 1 Increased EVAB will prospectively predict reduced PSU symptoms at subsequent measurement occasions at the within-person level.

Hypothesis 2: Delay discounting will mediate the within-person effect of EVAB on subsequent PSU symptoms.

Hypothesis 3 Between-person differences in EFT will predict daily life PSU symptoms through the mediation of within-person EVAB.

Hypothesis 4: Between-person differences in EFT will predict daily life PSU symptoms through the mediation of within-person delay discounting.

Hypothesis 5 Between-person differences in EFT will predict daily life PSU symptoms through a serial mediation pathway involving within-person EVAB and delay discounting.