A single on-screen notification is enough to knock the brain off a demanding task for roughly seven seconds, according to a study by Swiss psychologists published in Computers in Human Behavior. The researchers, from the University of Lausanne, argue that the real cost of smartphones to attention lies not in total screen time but in the constant stream of brief interruptions, and that messages people believe are personally relevant cause the biggest disruption. Their practical conclusion: during complex work, switch off every alert that is not urgent.
A tired man at work with a smartphone
What you need to know
- 180 students completed a Stroop attention test while simulated push notifications appeared at the edge of their computer screens.
- After each notification, participants slowed down and made more errors for four consecutive trials, which amounted to about seven seconds.
- Participants who believed the notifications were their own real social media messages showed the largest cognitive disruption.
- The researchers identified three drivers of distraction: the sudden visual appearance of an alert, an ingrained habit of checking the phone, and the expectation of important information.
How the experiment worked
To measure precisely how long a notification disrupts thinking, the researchers recruited 180 students and asked them to complete the classic Stroop test, a tool psychologists use to assess selective attention and cognitive flexibility.
In the Stroop test, participants see the names of colors printed in a font of a different color. The word “red,” for example, might appear in blue letters. The participant must name the color of the font while ignoring the word itself, a task that demands sustained concentration.
While participants worked through the test, notifications designed to mimic smartphone push messages periodically popped up at the edge of the computer screen. Analysis of reaction speeds showed that after each alert, participants became slower and made more mistakes. The slowdown lasted for exactly four consecutive test trials, which corresponded to about seven seconds.
Personal messages are the most distracting
The team also examined whether the content of a notification affects how much it disrupts attention. Participants were split into three groups, each shown a different type of alert.
The first group was told that their personal phones had been synced with the work computer, so the notifications on screen were their genuine social media messages. The second group saw generic notifications from unfamiliar sources. The third group saw heavily blurred banners whose text could not be read.
The largest cognitive disruption occurred in the first group. The researchers’ interpretation is that the brain responds to the personal relevance of a message: when we believe information concerns us directly, the nervous system automatically assigns it top priority and overrides the current task. In their published findings, the authors single out three main causes of distraction: the sudden visual appearance of an alert on screen, a formed habit of checking the phone, and the anticipation of important information.
Why fragmentation matters more than screen time
Conventional digital-wellbeing tools focus on the total time a person spends on their phone. The Swiss psychologists argue this is not the most meaningful measure. In their view, the real problem is fragmentation: dozens of short interruptions across a day do more damage to cognitive performance than an hour of uninterrupted scrolling.
A woman writing in a notebook next to a glowing smartphone on a desk
Even if you never open a message and simply swipe it away, the brain has already spent resources recognizing the stimulus and deciding what to do with it. After those lost seven seconds, so-called attention residue sets in: it takes additional seconds, and sometimes minutes, to regain the depth of immersion in the task that existed before the alert.
What this means in practice
According to the University of Lausanne researchers, the average user receives around one hundred notifications a day. Multiplied by the time lost to each lapse in concentration, that suggests the brain spends a significant share of the working day in a state of fragmented focus. The researchers’ recommendation is to fully disable non-urgent notifications during demanding work.
Limitations to keep in mind
The findings come from a single laboratory study using a controlled attention test with a student sample, and the seven-second figure reflects performance on that specific task rather than a measurement taken during real-world work. How the effect scales across other tasks, age groups, and notification settings is not addressed in the source. The claim that fragmented interruptions are more harmful than long continuous screen time is the researchers’ argument rather than a direct comparison tested in this experiment.
