← StudyX Devlog

Does Too Much Smartphone Use Hurt Your Focus?

Hiroki ObaraHiroki Obara · DeveloperBrainDojoHow-To
Does Too Much Smartphone Use Hurt Your Focus?

People who blocked the internet on their smartphones for two weeks got better at a task that measures sustained attention. The trial, by Castelo and colleagues, was published in PNAS Nexus in 2025. The authors write that the gain was about the same size as ten years of age-related decline on that task.

The claim that heavy phone use wrecks your focus is everywhere. The research behind it comes in two kinds, and they are not equally strong. One kind compares heavy users with light users. The other asks people to actually cut back and measures them before and after. This post looks at both: what each has found, and where the results split.

Comparing heavy and light users

The study most often cited is a 2009 paper in PNAS by Ophir, Nass and Wagner. It did not look at smartphones as such. It looked at “media multitasking”: using more than one medium at the same time, such as texting while watching TV, or listening to music while searching the web.

The authors built a questionnaire that scores how much of a person’s media time is spent on more than one medium at once. They then compared people with high and low scores on standard tests of attention and memory. Heavy media multitaskers were more easily thrown off by irrelevant things around them and by irrelevant items held in memory. They also did worse at switching between tasks, which the authors put down to a weaker ability to shut out the task they were not doing.

This was a comparison, and a comparison cannot say which way the arrow points. Media multitasking might make people more distractible. People who are already distractible might also simply multitask more.

Replications split

Later studies asked the same question, and not all of them found the same thing.

In 2017, Wiradhany and Nieuwenstein published two replication studies and a meta-analysis in Attention, Perception, & Psychophysics. Across their replications they ran 14 tests. Five showed a significant effect in the direction of more distraction for heavier media multitaskers, and only two of those held up under a stricter Bayesian analysis.

Their meta-analysis pooled 39 effect sizes from all the published studies. It found a weak but significant link, which disappeared once they corrected for small-study effects, the tendency of small studies to report larger effects. The authors concluded that they question whether a link between media multitasking and distractibility in lab tasks exists at all.

A year later, Uncapher and Wagner, the second of whom was an author of the 2009 paper, reviewed the field in PNAS. They described the literature as still sparse, with both convergent and divergent findings. On balance, they wrote, heavier media multitaskers tend to perform worse in a number of cognitive areas, although many studies find no difference. When a difference does appear, it tends to be on tasks that depend on keeping attention on a goal over time. They called for research that can settle the direction of cause.

Why the results don’t line up

There are several possible reasons.

One is how use is measured. Most comparison studies ask people how much they use their phones or other media. A 2021 meta-analysis in Nature Human Behaviour by Parry and colleagues pooled 106 effect sizes from studies that had both self-reports and logged usage. Self-reports correlated only moderately with the logs and were rarely an accurate reflection of them. Scales of “problematic” use tracked the logs even less well.

If the amount of use is measured with that much error, it is no surprise that its link with attention shows up in some studies and not in others.

Studies also use different tasks to measure attention. And the direction of cause remains open. No number of comparison studies can solve that last problem.

A trial that cut use

That is why a trial that changes the amount of use carries weight. Castelo and colleagues randomly split 467 iPhone users into two groups.

One group blocked all internet on their phones for the first two weeks, both mobile data and Wi-Fi, using an app that also recorded whether the block was on. Calls and text messages still worked, and they could still go online on a computer or other device. The other group carried on as usual for the first two weeks and did the same block in the second two weeks.

Attention was measured with a task, not a questionnaire. Photos of cities and mountains appear one after another. You press a key for each city and hold back for the occasional mountain. The task takes about five minutes and measures how well you keep telling them apart without drifting.

The results:

  • The group that blocked first improved on the attention task over the two weeks. The group that carried on as usual over the same period did not change.
  • Daily phone screen time in the group that blocked first fell from 314 to 161 minutes.
  • Comparing before and after the block, 58.5% of participants improved on the attention task.

The authors explain part of the gain through how people spent their time. While the internet was blocked, participants spent more time socializing in person, exercising and being in nature, and these changes partly accounted for the improvements.

What this trial cannot tell us

The authors list the trial’s limits themselves.

The biggest is that few people stuck to the plan. Of the 467 who signed up, 119, or about 25.5%, kept the block on for at least 10 of the 14 days. When the authors analyzed everyone, including those who did not stick to it, attention still improved.

Participants were also people who wanted to cut down on their phones. They knew the study was about smartphones, so expectations may have played a part. The comparison group was a waitlist that did nothing. Only iPhone users took part. Computers and tablets were not blocked, so it is not known which kind of use matters most.

And what the trial showed is that blocking the internet improved attention. It does not show whether everyday use wears attention down over years.

So does it hurt focus?

Putting it together:

  • Studies that compare heavy and light users disagree. A set of replications and a meta-analysis concluded that the link may not be there at all.
  • Those studies usually rely on self-reported use and cannot tell cause from effect.
  • A trial that cut actual use found better attention scores after two weeks, but only about a quarter of people kept the block on as planned, and the design has limits.

There is not enough evidence to say flatly that heavy phone use damages focus. There is, though, experimental evidence that cutting back can raise scores on a sustained attention task. What happens when a phone just sits on the desk, or when a notification goes off, is covered in Do Phone Notifications Break Your Focus Even If You Ignore Them?

References

BrainDojo is also a phone app. A session can start at about ten seconds, and Today’s Training is picked for you each day. Notifications are kept low-key, and you choose your own reminder times. The Attention Boost lane has trainings for holding and switching attention.

Every training except the newest ones is free to play, and the free version shows ads. BrainDojo Plus removes the ads and lets you play the new trainings at any time. Your first session is covered in Getting Started with BrainDojo.

Download on the App Store Get it on Google Play