Monday, 4 March 2013

Are we now blasé about brain scans?

People are so awestruck by neuroscience, the briefest mention of brain-based jargon or glimpse of a brain scan is enough to send their critical faculties into a flutter. Or so they said. But now a new study finds that in fact most people are singularly non-wowed by the technical brilliance of brain scan images.

Robert Michael and his colleagues performed ten replication attempts of a hugely influential finding published in 2008. Back then David McCabe and Alan Castel reported that undergrad students were more persuaded by a neuroscience news story when it was accompanied by a picture of a brain scan, as compared with a bar chart or no image. The result is mentioned frequently in the popular press as evidence of our neuro-enthrallment. It receives about 40 scholarly citations a year, but until now no-one has checked if the effect is real.

Seven of Michael's ten replications were performed online, three with paper materials, together involving nearly 2000 participants, including members of the public and students. As in the McCabe and Castel study, participants read a news item about brain scans being used to detect criminals. Afterwards the participants said if they agreed with the story's conclusion that brain scans can be used as a lie detector.

Combining the results from the McCabe and Castel study with the new data, overall the presence of a brain scan in the news story had only a tiny effect on participants' answers. On a 4-point response scale (from strongly disagree to strongly agree with the story), this reflected a shift of just 0.07 points or 2.4 per cent in agreement. "The image of the brain exerted little to no influence," the researchers said. The effect of the brain scan image didn't vary with the format of the study - online vs. paper. Participant age and education level also made no difference.

Past research outside of the neuroscience context has shown that images can make accompanying text more understandable and persuasive. The remarkable ineffectiveness of a brain scan in the current replications is therefore something of a puzzle. One explanation is that the impact of the image will vary according to the neuroscience training of the observer. "To people who may not understand how fMRI works, or even where the frontal lobes are, seeing an image of the brain may not be any more helpful than seeing an ink blot," the researchers said. Future research will need to test this.

Another possibility is that people have grown more sceptical of neuroscience since the 2008 McCabe and Castel finding was published. To test this possibility, Michael and his colleagues performed five online replications of another influential study - the 2008 discovery that people were more impressed by bad explanations when they contained gratuitous neuroscience language. This finding was replicated, arguing against the idea that people have become inoculated more generally against the persuasive power of neuroscience.

In the replications of McCabe and Castel, perhaps the addition of a brain scan image failed to make the lie detection news story more convincing because that story already contained persuasive neuroscience language. Regardless, this new paper adds to evidence showing the failure of brain images to sway jurors. And Michael's team said (quoting Martha Farah) it shows "the 'amazingly persistent meme of the overly influential image' has been wildly overstated." Recently, Farah and her colleague Cayce Hook described this phenomenon as the “seductive allure of ‘seductive allure’".


Michael, R., Newman, E., Vuorre, M., Cumming, G., and Garry, M. (2013). On the (non)persuasive power of a brain image. Psychonomic Bulletin and Review DOI: 10.3758/s13423-013-0391-6

--Further reading--
The power of blobs on the brain
Are Brain Scans Really So Persuasive?

Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.

1 comment:

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