Friday, 11 November 2005

Why did I do that?

What if free will is an illusion? Perhaps we make up the reasons for our actions retrospectively, tricking ourselves into believing we know why we did what we did, when really our behaviour was involuntary. A new study lends credence to this suggestion by demonstrating a phenomenon the authors dub ‘choice blindness’.

One hundred and twenty participants were shown 15 pairs of female faces (taken from here). For each pair they had to say which of the two faces they found more attractive, and on a fraction of trials they had to say why they’d made that choice, in which case the photo of the face they’d selected was slid across the table to them so they could look at it while they explained their choice. Crucially, on a minority of these trials, the researchers used sleight of hand to surreptitiously pass the participant the photo of the face they had just rejected, rather than the one they’d chosen.

Bizarrely, only about a quarter of these trick trials were noticed by participants, despite the fact the two faces in a pair often bore little resemblance to one another. Even stranger was the way the participants then went on to justify choosing the face on the card they were holding, even though it was actually the face they’d rejected. It’s not that participants weren’t paying attention to the face they’d been passed – the justifications they gave often related to features specific to this face, not the one they’d actually chosen. Independent raters who compared participants’ verbal explanations for choices they had made (non-trick trials), with their explanations for the choices they hadn’t made (trick trials), found no differences in amount of emotional engagement, degree of detail given, or confidence.

The researchers said “Participants failed to notice conspicuous mismatches between their intended choice and the outcome they were presented with, while nevertheless offering retrospectively derived reasons for why they chose the way they did. We call this effect choice blindness”.

Lead researcher Petter Johansson told The Digest that interviews with the participants afterwards confirmed the choice blindness effect was real rather than a consequence of participants being afraid to say something odd was going on at the time.
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Johansson, P., Hall, L., Sikstrom, S. & Olsson, A. (2005). Failure to detect mismatches between intention and outcome in a simple decision task. Science, 310, 116-119.

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

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