In 2008, a team of psychologists from the University of Michigan apparently found a simple memory task that could boost intelligence. They asked volunteers to watch a sequence of symbols while listening to a series of letters. Holding both streams of information in their heads, they had to say if the current symbol or letter matched the one from a few cycles back. This memory-based “dual n-back” task seemed to improve the volunteers’ fluid intelligence—a general ability to solve problems that goes well beyond mere memory. The team said that their study opened up “a wide range of applications”.
Walter Boot from Florida State University and Daniel Simons from the University of Illinois at Urbana-Champaign disagree. They think the study had a critical weakness: it compared the people who did the n-back task with a control group who did nothing. Those who did the memory training may have expected to gain a temporary boost in intelligence, memory or mental abilities. Those who sat and waited wouldn’t have expected anything.
For decades, we’ve known that our expectations can wield a huge influence over our behaviour and our bodies. This is why new medicines are tested in double-blind randomised trials, where neither doctors nor patients know who’s getting a drug and who’s just getting a placebo. If the trials weren’t blinded, the patients who got the drug might get better simply because they expected to get better—the infamous placebo effect.
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