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You are solving a chemistry worksheet. Your phone buzzes, you reply, you go back to the worksheet, and then a video autoplays in the other tab. It feels as though you are getting several things done at once. This post explains what task-switching experiments show about that feeling, why it costs you time even when your marks seem fine, and how to set up study sessions that avoid the cost.
Can the brain really do two things at once?
For simple, practised actions, such as walking while talking, yes. For two tasks that both need thinking, the answer from decades of lab work is mostly no. What looks like multitasking is rapid switching.
Rubinstein, Meyer and Evans (2001) ran four experiments in which people either repeated one task or alternated between tasks, such as classifying shapes by different rules or solving arithmetic with different operations. Alternating produced switching-time costs. Those costs grew when the rules were more complex and shrank when people had clear cues about which task came next. The authors proposed that each switch has two stages: shifting your goal, then activating the rules for the new task.
A chemistry problem and a group chat use very different rules. Each time you move between them, you pay that set-up cost again.
Does multitasking hurt marks, or just time?
This is where the research gets more interesting than the usual warning. Bowman, Levine, Waite and Gendron (2010) had students read a textbook-style passage. Some exchanged instant messages before reading, some during reading, and some not at all. On the comprehension test, the three groups did not differ. But the students who messaged during reading took significantly longer to finish the passage, even after the time spent receiving and answering messages was subtracted.
So the cost showed up as time. For a student with five subjects and a fixed number of evening hours, lost time is a real cost: it is the revision you no longer have time for.
Are some people good multitaskers?
Many students believe they are, often because they grew up with phones. The evidence does not support the idea that frequent multitaskers get better at it. Ophir, Nass and Wagner (2009) compared heavy and light media multitaskers on standard attention tests. Heavy multitaskers were more easily distracted by irrelevant information and, surprisingly, did worse on a test of task switching.
A later review by Uncapher and Wagner (2018) adds caution: many studies found no difference between groups, and the research cannot yet say whether multitasking causes poorer attention or whether people with less focused attention multitask more. On the wider claim that young people are natural multitaskers, Kirschner and De Bruyckere (2017) reviewed the evidence and concluded that learners cannot multitask; they task switch, and that switching hurts learning.
The safe reading for a student: you are unlikely to be the exception, and practice at switching does not seem to make you better at it.
Why does switching feel productive?
Every reply or new tab gives a small sense of progress. The cost of switching is invisible because it is spread across many small delays: rereading a line you already read, finding your place in a derivation, recalling which formula you were about to use. You notice the messages you answered, not the twenty minutes the chapter took longer than it should have.
If the phone pulls you even when you are not using it, our post on whether a phone on the desk affects focus covers that separate question and its mixed replication record.
How do you study without switching?
Decide the one task. Write it at the top of the page: "Solve exercise 4.2, questions 1 to 8." A clear task makes it obvious when you have drifted.
Batch messages. Choose a block length you can manage, for example 40 minutes, then a short break where you check everything at once. You still reply to friends, just in one batch.
Make switching harder. Put the phone in another room or turn notifications off for the block. Close tabs that are not part of the task.
Leave a re-entry note. If you must stop, write one line: "Next: apply Hess's law to step 3." It cuts the time needed to restart, the same way a clear cue cut switch costs in the lab.
Keep switching between subjects for planned moments. Mixing physics and chemistry in one session is fine; switching every two minutes is not. Change subject at the end of a block, not in the middle of a problem.
When the urge to switch comes from being stuck, the fix is often a clearer path through the problem. The Fermi Problem Library has worked problems with a step-by-step solver that explains the reasoning rather than printing an answer, so you can get unstuck without leaving the task for a chat.
Tonight, try one 40-minute block with your phone in another room and note how much of the worksheet you finish compared with a usual evening.
