Mental fatigue and attention: four things worth noticing

Attention and memory

Mental fatigue has a shape. Once you can see the shape, you can plan around it instead of grinding through it, which is the whole reason it is worth describing. Four observations cover most of what you need.

This article covers ordinary everyday tiredness and what it does to your performance on attention tasks. It is not about any medical condition, and nothing here is diagnostic. If concentration gives you persistent trouble, raise it with a qualified professional.

1. Speed goes before accuracy

Your accuracy usually holds up when you are tired. What gives way first is time: how long each answer takes you, and how often a long pause turns up in the middle of something you have done a hundred times. On a speeded task, fatigue looks like a response time distribution going ragged at the edges, not like a run of errors.

Judge your own state by whether you are making mistakes and you will think you are fresher than you are. The slowdown gets there first. The mistakes take their time.

2. Sustained attention fails before selective attention

Attention is not one capacity, which is the part people skip. Picking the relevant item out of a cluttered screen, which is selective attention, holds up well when you are tired. Staying locked on something dull for twenty minutes, which is sustained attention, falls apart much faster.

Tired work goes better in short, well-defined pieces. Motivation has nothing to do with it, whatever the voice in your head says about discipline. You have run down the one capacity that long unbroken stretches depend on.

3. The cost of switching rises

Moving between two kinds of task always costs you something. Fatigue raises the price. The same alternating pattern of work you handled fine in the morning drains you out of all proportion by late afternoon.

Stop switching rather than trying to switch better. Group similar work together and take a duller afternoon in exchange for a cheaper one. Boredom is the fee here, and it is worth paying.

A tired hour spent on one kind of task buys you considerably more than a tired hour spread across three.

4. Interest partially masks it

Fatigue effects shrink on tasks you find engaging, which is why you can be too tired to answer email and then absorbed in something demanding an hour later. The effect is real. Your tiredness was not fake.

It is also a trap, and a flattering one. Interest borrows against the same capacity instead of topping it up, and the bill turns up later. Use an engaging task to prove you are fine and you tend to buy yourself a harder crash.

A set of lap times shows it plainly. Late in a stint a driver still hits the same apexes and brakes at the same boards, so nothing looks or feels wrong from the cockpit, while the times drift a couple of tenths at a time. Accuracy holds. Speed leaves without telling anyone.

Noticing it earlier

Trust what you do over what you feel. You re-read the same sentence. You lose the thread of your own paragraph. You reach for your phone between every small step, which is the one people notice last in themselves. All three turn up before you notice you are tired.

A short timed task makes the point sharper, because you can measure response time and you cannot argue with it. Comparing a quick self-assessment in the morning against one late in the day is a blunt instrument, and it still beats asking yourself whether you feel tired.

Working with it rather than against it

Match the work to the capacity you have left. Demanding, tangled work belongs in the window where your sustained attention is still intact. Routine work with clear edges survives fatigue well, which is the cheap win most people leave on the table. Decide which is which in advance, while you are fresh enough to judge, and you have taken most of the benefit.