Stroop Effect

Maybe the image is right and you're wrong. Maybe you've always been wrong. Who's to say? Look again. Think about it – but don't take too long.

Jun 11, 2026

True BLUE design at REMO, 1990. Design credit: Remo Giuffré

In 1990, a T-shirt design was added to the REMO General Store range that inadvertently demonstrated one of the most famous experiments in the history of cognitive psychology. On the front of the T-shirt was the word “BLUE” – printed boldly in red ink. On the back: “TRUE” – this time printed in actual blue. A striking combo. Visually arresting. But also, as it turns out, mentally confounding. Not recommended as a gift for the elderly.

Confused old people according to a Google image search

True BLUE (as it was named by REMO) is a textbook case of what’s called the “Stroop Effect” – a phenomenon first documented in 1935 by American psychologist John Ridley Stroop. It’s simple on the surface – participants are shown the names of colours (like blue, red, green) printed in mismatched ink colours and asked to say the colour of the ink, not the word itself. When the word “blue” is printed in red, the brain takes a beat longer to respond correctly. It’s not that you don’t know what red looks like. It’s that your brain processes the word faster than the colour, and the two signals collide.

John Ridley Stroop (1921–1968) > Stroop stimuli example

It’s a tiny but measurable moment of cognitive interference, and it says a lot about how we think. Reading, for most literate adults, is automatic – so much so that even when you’re trying not to read, you kind of do it anyway. Realising that your initial assumption is wrong, and identifying the colour of the word instead is a process that is not automated.

The Stroop test has since become a go-to tool for measuring attention, processing speed and mental flexibility. It’s used in everything from diagnosing neurological disorders to testing how tired someone is.

Anterior cingulate gyrus shows increased activity when viewing conflicting stimulus

Similarly, the emotional Stroop test is a psychological variation of the classic Stroop task, designed to reveal how emotionally charged words affect our attention and cognitive processing. Instead of neutral colour words like “blue” or “green,” participants are shown words with emotional significance, such as “death”, “love” or “failure” – each printed in various ink colours. The task remains the same: name the colour of the ink, not the word itself. But when the word carries emotional weight, people typically take longer to respond. This delay can reveal unconscious anxieties, trauma or emotional salience – and is often used in clinical settings to explore conditions like PTSD, depression or anxiety.

What makes the Stroop Effect enduringly interesting is how it taps into the strange friction between intention and automation. And it’s not alone. The world is full of everyday Strooplike stumbles. Two more examples:

1. The McGurk Effect. Watch a video of someone mouthing “ga”, while the audio says “ba”, and your brain hears “da”. What you see changes what you hear.

2. Trompe-l’oeil street art: A flat pavement painted to look like a deep hole can trigger vertigo. You know it’s flat, but your brain screams otherwise.