Science & Magic

Measure your switch cost

This measures the tax you pay for changing mental rules. A letter-and-digit pair appears in a grid. The row tells you which rule to run — and the rule keeps changing.

Top row Judge the letter: vowel or consonant

Bottom row Judge the digit: odd or even

F vowel · odd J consonant · even

Rest your index fingers on F and J and leave them there — the same two keys answer everything, so the only thing that changes between trials is the rule in your head. About 90 seconds. Nothing is sent anywhere; the result is yours to screenshot. (On a phone, tap the two buttons instead.)

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practice

letter

digit

practice done

Now the real thing

Same rules. Go as fast as you can while staying accurate. About 90 seconds.

Fingers back on F and J. Press Space when you're set.

your switch cost

–ms

repeat trials –

switch trials –

repeat · switch

attention.benphoon.dev/demo

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Scores drift with tiredness, caffeine and practice. One number isn't a verdict on anyone — the point is that the gap between switch and repeat is real, and it survives even when you know the switch is coming.