Monday, 10 January 2011

Three-year-olds show a bias for spotting snakes in a striking posture

Have we evolved to detect this threat?
We humans seem to have an innate predisposition to fear dangerous animals and other hazards that would have imperilled our ancestors - a phenomenon called 'prepared learning'. For example, when researchers in the 1980s used loud noises to condition people to fear the sight of snakes and guns, they found that people acquired a fear of the snakes much more easily, even though the noises matched the sound made by guns. A new study has built on that classic work by showing that children as young as three seem to be particularly adept at spotting snakes in a 'striking pose'.

Nobuo Masataka and his colleagues presented their participants with three-by-three arrays of pictures of snakes and flowers on a touch-screen. On each trial, eight of the pictures were of flowers with one snake picture, or vice versa, and the task was to touch the odd-one-out picture as quickly as possible. Twenty three-year-olds, 34 four-year-olds and 20 adults took part.

Participants of all ages were significantly quicker at the task when spotting a snake among flowers than when spotting a flower among snakes. For example, the three-year-olds took an average of 2735ms when a snake photo was the target compared with an average reaction time of 3283ms when the target was a flower. This was the case even though the children's parents said their offspring hadn't previously been exposed to real or toy snakes.

What's more, all the participants were extra quick at the task when the target picture was a snake in a striking pose: with the body coiled, the neck held in an s-curve and the head poised to strike. The three-year-olds' average reaction time for snakes in a strike pose was 2452ms compared with 2519ms for snakes in a resting position.

The new finding builds on the classic research into prepared learning by suggesting that there is a prototypical snake posture that humans are innately sensitive to. 'When a striking posture is taken by snakes,' the researchers explained, 'they display their specific morphological characteristics as signals towards the presumptive signal receivers so that the receivers will categorise them as snakes as efficiently as possible, be threatened and withdraw.'

An interesting question for future research is whether this is an evolutionary adaptation in snakes or in humans. In other words, did snake appearance and behaviour evolve in a way that exploited existing perceptual biases in humans and other animals, or did the human perceptual and attentional system evolve in such a way to become particularly attuned to snakes and snake behaviour?
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ResearchBlogging.orgMasataka, N., Hayakawa, S., and Kawai, N. (2010). Human Young Children as well as Adults Demonstrate ‘Superior’ Rapid Snake Detection When Typical Striking Posture Is Displayed by the Snake. PLoS ONE, 5 (11) DOI: 10.1371/journal.pone.0015122

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

5 comments:

  1. Surely the latter? How would it benefit snakes to evolve in lines with our pre-existing fears?

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  2. If there is indeed a prototypical snake posture that humans are innately sensitive to an even more interesting question is: How the heck can this be encoded in the genes???

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  3. The "how the heck can this be encode in the genes?" question applies to so many evolutionary adaptations for which we know for sure that it is purely genetic (e.g. preference of baby infants for beautiful faces of women = symmetrical faces = healthy women); and although the question is a tricky one, this is not the right place for a discussion about that, because we know for sure that these complex things CAN be encoded.

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  4. Is it easier to spot spaghetti amongst macaroni or macaroni amongst spaghetti? "The three-year-olds' average reaction time for snakes in a strike pose was 2452ms compared with 2519ms for snakes in a resting position." That's an improvement of 67ms, about 2.6%. Although human reactions and snake attacks do occur at this order of time, it is readily attributable to other factors, such as the very fact that humans interpret vertical and horizontal elements differently.

    And even if such complex things can be encoded in genetic information, would there even be a feasible mechanism for this to occur? In this case, 2.6% appears to be statistically insignificant for gradual change. Perhaps they got a "genetically defective" sample?

    Nice try, but the research doesn't say much.

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  5. More evidence for the innate ability to spot such threatening geometric shapes comes from the fascinating research of Christine Larson at UW-Milwaukee. See for example her 2009 article in Journal of Cognitive Neuroscience, "Recognizing threat: Simple geometric shapes activate neural circuitry underlying threat detection". Not only do subjects show a reaction time advantage for geometric shapes associated with phylogenetically relevant feared objects, they also preferentially recruit a neural network associated with threat detection for these shapes.

    While it might be difficult for us to conceptualize how evolution could encode such abilities in genes, the data are what they are. I agree with Eiko on this point.

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