Past research has found that people are faster and more accurate at recognizing positive words such as "happy" than negative words such as "mad," and similar effects are seen with pictures and sounds. This emotional bias is curious, given how people are equally good at remembering both positive and negative details of an event, such as words, pictures and sounds.
"What causes this difference?" said researcher Lars Kuchinke, an experimental psychologist at Ruhr University in Germany.
To see what triggers this positivity advantage, the researchers decided to experiment with caffeine. Caffeine helps lead to faster responses and fewer errors in simple mental tasks, and one might expect it would help people recognize both positive and negative words.
Scientists asked 66 volunteers to decide as fast and accurately as possible whether strings of letters they saw on computer screens were real words or not. Half the volunteers were given a lactose pill that had no effect on results, while the other half were given tablets containing 200 milligrams of caffeine 30 minutes before testing, equivalent to about two or three cups of coffee.
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