Picture a person reading a message from a friend. A second message arrives from someone else. For a moment they are reading neither. Attention is the mind's narrow beam. It lights one thing that needs thought at a time, and moving it to another thing takes a moment.
Drop the thread→Find the other→Find your place→Think again
That moment is the cost of a switch. The mind drops one thread, finds the other, and finds its place in it. Practised things, like walking, need no beam at all. But two things that both need thought cannot share the beam. They take turns, and every turn is paid for.
The sum
vsvs
The message
A person is working out a sum. A message lights up. They read it and go back to the sum. What has the message cost the sum?
A switch: the moment to drop the sum, read, and find their place in the sum again.
Right. Two things that needed thought took turns. Each turn has a cost, even when the message turned out to be nothing.
The whole sum. They will have to start again from the top.
Not yet. A switch costs the place in the thread, not the thread. The earlier steps are still done; finding where they were is the cost.
Nothing. The eye glanced at it and the sum kept going by itself.
Not yet. A sum is not walking. It needs the beam, and while the beam was on the message the sum was waiting, not running.
2004One screen
↓→
about 150 secondsBefore switching
Gloria Mark, a researcher at the University of California, Irvine, has measured this on real screens since 2004. She timed how long people in offices stayed on one screen before switching to another, first with a stopwatch and later with software. In 2004 the answer was about two and a half minutes.
Slide the marker to your guess. In her studies from 2016 on, how many seconds did people stay on one screen before switching?
Slide the marker to where you think the answer is, then press Lock. Nothing is scored.
1234
your guess · 0 s
the answer · 47 s
0 s90 s180 s
100 s
26060 s
3120120 s
4180180 s
Your guess: —
Under a minute, and under a third of the 2004 reading. A switch does not feel like something that happens every three quarters of a minute. The study measured how often the beam moved, not how well it thinks.
2004150 seconds on one screen
201275 seconds on one screen
2016 on47 seconds on one screen
Here are her three readings. They measure how often the beam moved, not how well people think. What changed is what sits in front of them, more windows, more messages, screens that light up, and a habit: Mark found people interrupt themselves about as often as they are interrupted. Every switch is paid by the person whose beam moved.
Picture an hour of work on one thing. Each switch costs about one minute to find your place again, a made-up round number. Move the switches in the hour and watch how much of the hour is left for the thing itself.
On the thing60 minutes, made up
Finding your place0 minutes, made up
Switches in the hour: 0 switches
No switches: the whole hour goes to the thing.
On the thing50 minutes, made up
Finding your place10 minutes, made up
Switches in the hour: 10 switches
Ten switches, ten minutes finding your place: fifty minutes left.
On the thing30 minutes, made up
Finding your place30 minutes, made up
Switches in the hour: 30 switches
Thirty switches, one every two minutes: half the hour is spent finding your place.
On the thing0 minutes, made up
Finding your place60 minutes, made up
Switches in the hour: 60 switches
Sixty switches, one a minute.
At sixty switches an hour, about one a minute, how much of the hour goes to the thing itself?
Half. A switch is quick, so the thing still gets most of the hour.
Not yet. The frames charged one minute per switch, and sixty switches is sixty minutes. Quick, done sixty times, is the whole hour.
All of it. Finding your place is part of the work.
Not yet. Finding where you were adds nothing new to the thing. It only gets you back to where you already were, which is why the frames count it apart.
None. Every minute is spent finding the place that was just lost.
Right. Sixty switches at a minute each is the whole hour. The beam never gets back to the thread before the next switch comes. Mark's 47 seconds is even more switches than this; the minute per switch is still made up.
Move the control.
A lightfree to send
↓→
A switchpaid by the reader
Notice who pays. The message that lit up cost its sender nothing. It cost the reader a switch, whether the message mattered or not. The screen does not pay for the beam it moves. The person does, every time. The next lesson asks why a hand keeps going back to it.
Each card is two things done together. Do they run together, or take turns?
One card at a time. Tap the pile it belongs to.
Card 1 of 5
Walking and talking with a friend
Reading a message and listening to a teacher explain a sum
Humming a tune while washing up
Writing an essay and following a group chat
Watching a film while scrolling a feed
Walking and talking with a friend → Run together
Not yet. Together. Walking is practised and needs no beam, so the talk has it to itself.
Reading a message and listening to a teacher explain a sum → Take turns
Not yet. Turns. Reading needs thought, so while the beam is on the message the teacher's words go past unheard.
Humming a tune while washing up → Run together
Not yet. Together. Neither needs the beam; both are habits the hands and mouth run on their own.
Writing an essay and following a group chat → Take turns
Not yet. Turns. A sentence being written needs the beam, and each new message pulls it away; the place in the sentence is lost every time.
Watching a film while scrolling a feed → Take turns
Not yet. Turns. A plot needs following, and following needs the beam. When the feed has it, the film goes on without a watcher.
2Run together
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3Take turns
Right. Two run together, three take turns. The test is not how easy a thing looks. It is whether it needs thought. Two things that need thought cannot share the beam, so they alternate, and the alternating is the cost.
A tipevery 10 minutes
++
A studentmid-problem
A homework app sends a cheerful tip every ten minutes to keep students going. Using this lesson, what does each tip do to a student in the middle of a problem?
It helps, because the tip is about the work.
Not yet. Being about the work does not spare the switch. The beam still leaves the problem and has to find its way back into it.
Nothing, because a student can read a tip without stopping.
Not yet. Reading needs thought, and so does the problem. Two things that need thought take turns; that is the whole lesson.
It costs a switch: the beam moves to the tip and back, and the student has to find their place.
Right. Even a helpful message needs the beam. Six an hour is six switches, each paid by the student and none by the app.
Lesson complete
One thing that needs thought at a time; every switch is paid by the reader, not the screen.