What the Research Says About Phones and Focus

Data · 2025-05-08 · 7 min read

Forty-seven seconds on one screen. A smartphone on the desk. Two weeks without mobile internet. What studies of attention found, where they disagree, and what that suggests for focus tools.

In Gloria Mark's workplace studies at UC Irvine, the average time people spent on one screen before switching fell from about two and a half minutes in 2004 to 47 seconds in a 2016 study, according to Mark.

Forty-Seven Seconds

Gloria Mark began timing how people at work moved between tasks in the early 2000s, first with stopwatches and later with logging software. Describing the work behind her 2023 book Attention Span, she gives these figures for the average time on a single screen before switching: about two and a half minutes in 2004, 75 seconds in 2012, and 47 seconds in a 2016 study, where the median was 40 seconds.

The number is often misquoted. It isn't a limit on the human brain, and not every switch is a distraction. It describes how office workers at computers moved between screens. Mark also says people are just as likely to interrupt themselves as to be interrupted by a notification: they switch away on their own, without anything prompting them.

Interrupted Work Is Faster, and Costs More

A 2008 experiment by Mark, Daniela Gudith and Ulrich Klocke found something counterintuitive. People who were interrupted while answering emails finished the task in less time, with no loss in quality. The cost showed up elsewhere: interrupted participants reported more stress, higher frustration, more time pressure and more effort. They compensated by working faster, and paid for it.

The Phone on the Desk

In 2017, Adrian Ward and colleagues published 'Brain Drain: The Mere Presence of One's Own Smartphone Reduces Available Cognitive Capacity'. The study varied where participants' phones were (on the desk, in a pocket or bag, or in another room) and tested their performance on cognitive tasks. The idea that a phone's mere presence uses up attention spread quickly.

It has not held up cleanly. A pre-registered replication by Ruiz Pardo and Minda, published in Acta Psychologica in 2022, repeated the second experiment with the same phone locations and found no difference between them on a working-memory task or a go/no-go task. A 2023 meta-analysis of 22 studies (Böttger, Poschik and Zierer) reported a significant overall negative effect of smartphone use and presence, but with substantial variation across studies and cognitive domains. The fair summary is that the evidence is mixed, and the size of any cost from a nearby phone is still argued.

Two Weeks Without Mobile Internet

A more recent test came in 2025. In a randomised trial published in PNAS Nexus, Noah Castelo and colleagues asked 467 iPhone users to install an app that blocked mobile internet for two weeks, while keeping calls and texts. In the group that blocked first, average daily screen time fell from 314 minutes to 161. That figure covers only the participants in that group who uploaded screen-time screenshots at all three time points, not everyone assigned to it.

467: Participants in the 2025 trial
314 → 161: Daily minutes, screenshot subgroup
91%: Improved on at least one outcome
47 sec: Average time on one screen, 2016 study

Participants improved on a measure of sustained attention and reported greater well-being, and 91% improved on at least one of the measured outcomes. The main results count everyone as assigned, whether or not they complied, and the authors report effects for compliers separately. The study also showed how hard this is: only about a quarter (119 of 467) kept the block active on at least 10 of the 14 days. A full cut-off is hard to keep up, and most people didn't.

What This Suggests for Focus Tools

Self-interruption is common, so a moment of friction at the point of reaching for an app does more than a reminder.
All-or-nothing cut-offs are hard to keep, so pausing a few chosen apps for a set session may be easier to stick with.
Interruption carries a stress cost, so a focus tool should not add guilt, scores or penalties of its own.
Attention data is personal, so a focus tool shouldn't need to record what you do elsewhere on your phone.

How HushZone Puts This Into Practice

HushZone pauses the apps you choose during a focus session, using Apple's Screen Time shield. When you open a paused app, 'Back to focus' is always the first choice. With the shield set to Soft, 'Open anyway' takes a second tap after a short pause; set it to Strict and that option goes away until the session ends.

Every session adds rows to a glass-bead weave, so focused time becomes something you can see. Weekly targets have rest days built in, and drifting away leaves a little gold in the cloth, not a penalty. Insights shows plain numbers, with no scores and no leaderboards.

None of it requires watching you. HushZone has no account, no analytics and no third-party SDKs, and it makes no network requests of its own. Your sessions and weaves stay on your iPhone.

Sources

Annie Duke's newsletter, 'Q&A with Gloria Mark, Author of Attention Span: A Groundbreaking Way to Restore Balance, Happiness and Productivity' (page read October 29, 2026). https://annieduke.substack.com/p/q-and-a-with-gloria-mark-author-of
Gloria Mark, Daniela Gudith and Ulrich Klocke, 'The Cost of Interrupted Work: More Speed and Stress', CHI 2008 proceedings, ACM. https://www.ics.uci.edu/~gmark/chi08-mark.pdf
Adrian F. Ward, Kristen Duke, Ayelet Gneezy and Maarten W. Bos, 'Brain Drain: The Mere Presence of One's Own Smartphone Reduces Available Cognitive Capacity', Journal of the Association for Consumer Research 2(2), April 2017 (bibliographic record only). https://doi.org/10.1086/691462
Ana C. Ruiz Pardo and John Paul Minda, 'Reexamining the brain drain effect: A replication of Ward et al. (2017)', Acta Psychologica 230, October 2022 (abstract via Europe PMC). https://doi.org/10.1016/j.actpsy.2022.103717
Böttger, Poschik and Zierer, 'Does the Brain Drain Effect Really Exist? A Meta-Analysis', Behavioral Sciences 13(9), 2023 (abstract via Europe PMC). https://www.mdpi.com/2076-328x/13/9/751
Castelo, Kushlev, Ward, Esterman and Reiner, 'Blocking mobile internet on smartphones improves sustained attention, mental health, and subjective well-being', PNAS Nexus 4(2), pgaf017, February 2025. https://academic.oup.com/pnasnexus/article/4/2/pgaf017/8016017