02 July 2010

Persuasion and other failures of will (but trust me on that sunscreen)

ResearchBlogging.orgYou don't have to read this. You could stop at any time. Couldn't you?

Everyone is going to say "Yes" to that question. We love to think that we are masters of our fate, captains of our destiny, our choices are ours alone. That notion is crucial to the ethical concept of agency, legal matters of intent, and much more.

But I'm sure everyone has had a moment like in video below. It starts at 1:58 and runs to 3:00:

It's that moment where you stop yourself, and go, "What am I doing?"

We don't always know why we do what we do. This idea probably got its biggest push from Sigmund Freud. Freud has a lot to answer for, because so much of his psychology is wrong, but his notions about the unconscious were revolutionary . Two articles have recently appeared that both lend support, in broad strokes, to the important of unconscious decisions.

I'll start with the empirical, by Falk and colleagues, who looked at what happens in the brain when you try to persuade somebody of something. They took a bunch of volunteers, and tried to get them to use sunscreen every day. This research was done in sunny California, so it's relevant for the people there.

I'm not sure that was the exact material they used, but you get the idea.

While showing their educational material to 20 subjects, the authors took fMRI brain scans, paying particular attention to the medial prefrontal cortex. Falk and company also asked their subjects if they planned to used more sunscreen.

After a week, they asked the subjects back, and checked on their sunscreen use.

What people said they were going to do was not significantly correlated with what they did do. This might be called the "New Year's effect."

The fMRI signal in the medial prefrontal cortex (remember, taken beforehand) was significantly correlated with what people actually did. The brain scan was a better predictor of actual behaviour than people's own statements about their intentions.

The researcher do note that they are taking the subject's word that she or he used sunscreen. They argue, though, that people would probably tend to report using sunscreen consistent with their stated intention, so if anything, the relationship between the initial intention and sunscreen use - which was not significant in the first place - was inflated.

The brain scan explains about 25% of the behavioral variation, so the effect is not huge. But still, this experiment is important is that it's part of a larger emerging enterprise that chips away at the notion that our conscious decisions cause, or are independent of, neural activity. You can't argue that very well when the neural activity precedes conscious decision and predicts it better.

Along these lines, a new review by Custers and Aarts argues that everything a human being need to create and act towards a goal can all occur unconsciously. This paper deal more with psychology than neuroscience. Interestingly, it seems to suggest that subliminal messages - once oversold, now largely ignored - can have some effects on behaviour under some circumstances.


Falk, E., Berkman, E., Mann, T., Harrison, B., & Lieberman, M. (2010). Predicting Persuasion-Induced Behavior Change from the Brain Journal of Neuroscience, 30 (25), 8421-8424 DOI: 10.1523/JNEUROSCI.0063-10.2010

Custers, R., & Aarts, H. (2010). The Unconscious Will: How the Pursuit of Goals Operates Outside of Conscious Awareness Science, 329 (5987), 47-50 DOI: 10.1126/science.1188595


Disgruntled PhD said...

Subliminal priming is actually used extremely regularly in psychology, normally to examine the effects of particular primes on future behaviors and outcomes.

Just for your information. Google evaluative priming or just read an issue of the journal of personality and social psychology.

Thanks for the link though, looks very interesting.

Zen Faulkes said...

I was aware of priming, but my impression had been that its effects were more limited than the review paper indicated.