What do I want? Don't ask me: Choice blindness at the market stall

Imagine you sampled two jams, chose your favourite, and were then offered another taste of it before being asked to explain your preference. Would you notice that you'd been offered the wrong one, that you were actually tasting the jam you'd turned down? A new study conducted at a market stall by Lars Hall and colleagues found that even for tastes as dramatically different as spicy Cinnamon-Apple and bitter Grapefruit, fewer than 20 per cent of participants realised that they'd just tasted the jam they'd moments earlier turned down. Even after being told the truth, fewer than half said they'd suspected they'd been offered the wrong jam.

This striking lack of insight has been dubbed choice blindness. Before now, it had only been demonstrated for visual preferences, in relation to women's faces, in a lab environment. This new study finds the effect in the real world, and in the context of taste and smell (as well as choosing between pairs of jams, participants also used smell to choose between pairs of specialist teas including Pernod vs. Mango).

To test the choice blindness effect, researchers used sleight of hand and double-ended jam jars or tea jars with a divide in the middle. Each jar contained a different jam/tea option at each end. Participants were presented with a pair of jars and tasted/smelt a sample from each. Then, by surreptitiously inverting the jars, the researchers were able to offer participants a second taste/smell from what appeared to be the same jar they'd just selected as their favourite, but actually now contained the jam/tea choice that they'd turned down.

Remarkably, on trials in which the tea or jam had been swapped, participants were just as confident about their choice as they were on control trials. However, as you'd expect, participants more often detected that the jams/teas had been swapped when choosing between pairs that pilot work had established were more different from each other. Another twist was that some participants were told they could actually take away their favoured jam or tea as a reward. However, this made no difference to the rates at which they detected their choice had been swapped, thus undermining the idea that the choice blindness effect may have to do with a lack of motivation.

People's apparent lack of awareness about choices they themselves have just made not only raises awkward questions about the limits of conscious awareness, but surely also has real-world implications. The researchers put it this way: 'The fact that participants often fail to notice mismatches between a taste of Cinnamon-Apple and Grapefruit, or a smell of Mango and Pernod is a result that might cause more than a hiccup in the food industry, which is critically dependent on product discrimination and preference studies to further the trade.'
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Hall L, Johansson P, Tärning B, Sikström S, & Deutgen T (2010). Magic at the marketplace: Choice blindness for the taste of jam and the smell of tea. Cognition, 117 (1), 54-61 PMID: 20637455