In the field of Cognitive Science, when studying about the Stroop effect, the claim is often made that it had been used during the Cold War by the American counter-intelligence units in order to identify Russian spies.
the Stroop task became a tool for American intelligence officials during the cold war. A covert agent could claim not to speak Russian, but he’d take longer to answer correctly when looking at Russian words for colors.
The idea is that you can't control the effect that your native language has on your performance on this task, so it can be used to uncover your native language. Is there any historical evidence of this usage?