Ben Goldacre, The Guardian, Saturday 26 February 2011

Science is about disproving hypotheses, and no matter what the armchair conspiracy theorists tell you, torpedoing cherished ideas is a very good way to make a name for yourself in academia. Here are two fun ones from the literature this month.

Firstly: are sniffer dogs for real? Animals respond to humans, after all, and especially domesticated animals: that’s the point of them. This is why the placebo effect is so wonderfully effective in animals, and of course in children.

Clever Hans was a horse who could read, spell, perform arithmetic, handle fractions, and differentiate musical tones. But in 1907 a psychologist Oskar Pfungst found the horse was actually responding to his owner, and his audience, who unwittingly gave involuntary cues to the animal as he got nearer to tapping out the right answer with his hoof.

3 academics have now replicated this phenomenon in sniffer dogs. They took 18 dog and handler teams, certified for detection of drugs or explosives, where the dog was trained to indicate it had found something by standing next to it. They ran a search for drugs or explosives in a four room building, in one of four conditions. Sometimes there was nothing to find. Sometimes there was an empty box with a sign on it, telling the handler this was the target. Sometimes there was a box of delicious decoy sausages. And sometimes there was a box of decoy sausages, with a sign on it, telling the handler this was the target.

The dogs were supposed to do the searching work, and the handlers were supposed to ignore the signs. In no case were there any drugs or explosives, although the handlers thought there were.

The results were a smuggler’s dream come true. The “dogs” kept confidently finding the empty boxes, when the humans could see the marker saying where they were. So in reality, although the human handlers cheerily thought the dogs were finding these boxes, in fact it was the humans themselves, just like with Clever Hans. The dogs also found the sausages a lot (though they were supposed to be finding drugs and explosives), but they were twice as likely to do so when the handler saw a sign misleading them into believing this was the target. Overall, the handlers beliefs had a greater influence over what was found than the dogs. If you’re a smuggler, get a haircut and buy a suit.

Meanwhile, you’ll have heard all about brain scanners being the next horizon in lie detectors. Neuroimaging lie detectors work by watching areas of the brain which are known to exhibit modest changes in blood flow when you’re shown a stimulus that has “salience”, like the box of poison you used to kill your wife, perhaps.

In a new study, the experimenters taught their subjects how to fake that signal. The participants were put in a scanner, shown a series of dates, and asked if each was their birthday. One date was. If they tried to deny their genuine birthday, the brain scan gave them away: they had concealed knowledge, they recognised their date of birth but denied it, and the machine caught them 100% of the time.

But then they were given a faking strategy: whenever you see an irrelevant date second in the sequence, you imperceptibly move your left toe before clicking “no”, and so on. This introduced salience to the other dates, as well as the birthday date. The recognition of – and deception about – their birthday no longer stood out in their brain bloodflow activity, and the computer could only spot the subjects’ deception about their birth date 33% of the time. As a lie detector this is basically useless.

Sometimes, when I’m in a fanciful mood, I enjoy devices like brain-scanning lie detectors, and hi-tech sniffer dogs, because their appeal speaks to our desire for simple mechanical explanations in a complex world, and for machines to aggrandise intuition, or make it more sciencey. But I enjoy them mostly because – like the ridiculous new porno-scanners in US airports, that give staff a view of your breasts and penis – they show how much of security is about theatre rather than reality.