Blocking Smartphone Internet Reversed a Decade of Attention Decline
A 467-person RCT found that two weeks without mobile internet improved sustained attention by the equivalent of 10 years of age-related decline — plus mental health gains comparable to antidepressants.
The Attention Economy's Hidden Cost
The average participant in this study spent 314 minutes per day — over five hours — on their smartphone before the intervention began. This isn't unusual. But the question researchers at five universities asked was: what happens to your brain when you stop? Castelo, Kushlev, Ward, Esterman, and Reiner (2025), published in PNAS Nexus, conducted a preregistered, month-long randomized controlled trial with 467 participants to find out. The intervention was simple: block all mobile internet on participants' iPhones for two weeks using the Freedom app in locked mode, preventing any override. Calls and texts still worked. Participants could use the internet on laptops and other devices. Only the smartphone was restricted.
Objective Attention Gains
Sustained attention was measured using the gradual onset Continuous Performance Task (gradCPT) — a validated cognitive test that measures discrimination ability through signal detection theory, yielding a d-prime score. After two weeks without mobile internet, the intervention group showed significantly improved sustained attention (Cohen's d = 0.23 intent-to-treat; d = 0.26 treatment-on-treated). The authors contextualized this improvement as equivalent in magnitude to approximately 10 years of age-related attention decline, and about a quarter of the difference between healthy adults and those with ADHD. This was an objective cognitive measure, not a self-report — making the finding resistant to placebo effects.
Mental Health Effects Comparable to Antidepressants
The mental health improvements were even more striking. Using the DSM-5 Level 1 Cross-Cutting Symptom Measures (covering depression, anxiety, anger, social anxiety, and personality functioning), the intervention group showed improvements with a Cohen's d of 0.56 (intent-to-treat) and 0.68 for compliant participants. Depression symptoms specifically improved with a within-subjects effect size of dz = 0.56 — which the authors noted is larger than the meta-analytic effect of antidepressants and comparable to cognitive behavioral therapy. Subjective well-being also improved (d = 0.45). Overall, 91% of participants improved on at least one of the three measured outcomes: attention, mental health, or well-being.
What Filled the Gap
Mediation analyses revealed what participants did with their reclaimed time. They spent more time socializing in person, exercising, being in nature, and pursuing hobbies and reading. They slept approximately 18 minutes more per night. Screen time dropped from 314 to 161 minutes per day. The strongest mediator of both mental health and well-being improvements was improved self-control — the sense of autonomy over one's own behavior. Interestingly, none of these mediators explained the attention improvement. The mechanism by which blocking internet improved objective sustained attention remains unknown, suggesting the cognitive benefit may operate through a different pathway than the psychological benefits.
The Rebound and What It Means
After internet was restored, screen time rebounded from 161 to 265 minutes per day — still below the 314-minute baseline, but most of the way back. Some mental health gains diminished, though attentional awareness improvements appeared to persist. The study has important limitations: 83% of participants scored high on motivation to reduce phone use (self-selected sample), only 26% met strict compliance criteria, and iPhone users only were included. The comparisons to antidepressant effect sizes are across different populations and study designs. But the core finding stands: smartphone internet access imposes a measurable, reversible cognitive and psychological cost. The question for Cognic's users isn't just how to train attention through meditation — it's whether to stop undermining attention through their devices.
References
- [1]Castelo, N., Kushlev, K., Ward, A. F., Esterman, M., & Reiner, P. B. (2025). Blocking mobile internet on smartphones improves sustained attention, mental health, and subjective well-being. PNAS Nexus, 4(2), pgaf017.
- [2]Ward, A. F., et al. (2017). Brain drain: The mere presence of one's own smartphone reduces available cognitive capacity. Journal of the Association for Consumer Research, 2(2), 140-154.
- [3]Wilmer, H. H., Sherman, L. E., & Chein, J. M. (2017). Smartphones and cognition: A review of research exploring the links between mobile technology habits and cognitive functioning. Frontiers in Psychology, 8, 605.