Cognition · ~2 minutes

How fast can you compare?

Two short strings appear; decide as fast as you can whether they're the same or different. Thirty items, timed — a measure of processing speed, the cognitive throughput that sits underneath everything else you think.

30 items · Timed · Same / Different

You'll see two strings of letters and numbers. Hit Same if they're identical, Different if even one character differs. Go as fast as you can while staying accurate — both speed and mistakes affect your score. On a keyboard, use ← for Same and → for Different.

About this instrument

What this measures — and what it doesn't

Measures
Cognitive throughput

How fast you can perform a simple comparison and decide — a perceptual/processing-speed task in the digit-symbol tradition, distinct from simple reaction time.
Method
30 timed comparisons

A fixed block of same/different judgments on short strings, half matching and half differing by exactly one character. We time each response and total your correct judgments per minute.
Result
Speed × accuracy

An approximate percentile from your throughput, plus accuracy and average time per item. Near-chance responding is withheld, so fast guessing never reads as fast processing.
Limits
Honest limits

Timing depends on your device and whether you use touch or keyboard, so it's a directional signal, not an exact figure. A short block is a snapshot, not a clinical or diagnostic measure.

Questions

Before you begin

What is processing speed?

Processing speed is how quickly and accurately you can carry out simple cognitive operations — comparing, scanning, and deciding. It's a core cognitive ability (one of the index scores on major IQ batteries) and it underpins how fast you can think through more complex tasks, because slow low-level processing bottlenecks everything above it.

How is this different from a reaction time test?

Reaction time measures how fast you respond to a single stimulus — largely a motor-and-attention measure. Processing speed measures cognitive throughput: how fast you can perform an actual comparison and decision, repeated across many items. This test times your same/different judgments, so it captures thinking speed rather than just how fast you can press a button.

Why does the score combine speed and accuracy?

Because speed alone is meaningless if you're wrong. The score is your correct judgments per minute, so errors lower it and slowness lowers it. Answering fast but randomly won't help — if your accuracy is near chance for a two-choice task, the speed score is withheld entirely rather than rewarding guessing.

Is my data saved anywhere?

No. The entire test runs in your browser. Your responses never leave your device and nothing is stored or sent to a server. Refreshing the page clears everything.

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