Clash

The most famous interference test in psychology. A colored word appears, and a prompt tells you which to tap — the color you see, or the color you read. The rule flips between rounds, and because reading is automatic, doing the opposite is surprisingly hard.

The Science: The Stroop Effect (Stroop, 1935). Perhaps the most replicated finding in cognitive psychology — reading is so automatic that suppressing it is measurably harder than any other single act of attention.