To study how we perceive our environment, scientists created the illusion of being either Barbie doll-sized or gigantic.
Becoming Barbie. I'm Bob Hirshon and this is Science Update.
At the Karolinska Institute in Sweden, volunteers have been shrunk to Barbie doll size or turned into thirteen-foot-tall giants. It's all an illusion, but a surprisingly strong one.
Cognitive neuroscientist Henrik Ehrsson and his colleagues had volunteers lie on stretchers and look toward their feet. Subjects wore video headsets that showed them the body and legs of either a small doll or a giant mannequin.
So when you look down, you don't see your own body, you see the mannequin or doll's body from this sort of first person perspective, where you expect to see your own body.
To seal the effect, the researchers prodded the patients' real bodies with various tools, while doing the same to the fake bodies with proportionally sized instruments. Ehrsson says the illusion altered not only how the subjects perceived their own size, but how they judged the size and distance of objects in the room. I'm Bob Hirshon, for AAAS, the science society.
Making Sense of the Research
We're so used to living in our own bodies and getting around in the world that we tend to take certain aspects of this experience for granted. For example, what makes you perceive your body as your own? Is it what you feel, what you see, or just what you know? And does our perception of ourselves influence how we judge the world around us?
To put it another way: Suppose you woke up one morning and found you had shrunk to Barbie doll size. Would you feel mainly like you had become tiny, or that the world had become gigantic? That's the central question this particular experiment looked into.
A few years ago, Ehrsson's team showed that people can be tricked into believing they had swapped bodies with a mannequin. They achieved this by fitting volunteers with video headsets, which were linked to video headsets on a mannequin. When the volunteers looked down, they saw a video image of the mannequin's torso, legs, and feet, rather than their own. The researchers then stroked the mannequin's belly and the volunteer's belly at the same time, which added to the illusion that the volunteers were inhabiting the dummy's body. They recoiled when the researcher raised a sharp knife over the dummy's body, as if their own body were being threatened. The trick even worked when they used another live person instead of a dummy, so much so that when that other person shook hands with the volunteer, they felt as though they were shaking hands with themselves.
In this experiment, Ehrsson's team applied the same techniques to disproportionately large and small dummies. Sure enough, they were able to make people feel like they were inhabiting these bodies too. Then they tested how the volunteers perceived their environments. They found that people who inhabited smaller-sized bodies judged objects to be larger than people in giant bodies. In one experiment, the participants were asked to close their eyes, stand up and walk toward where they thought a particular object was. Those who felt Barbie-sized walked further than those who felt huge.
What's more, these effects didn't happen when the volunteers looked through the video goggles but hadn't been fully trained to take "ownership" of the body through the touch procedures. So it doesn't appear that the fake bodies were simply a visual distraction that made people misjudge size and distance; rather, the fake bodies only changed people's perception if they really felt like they were their own. The research suggests that our sense of self depends on external cues, and our sense of the environment depends on our sense of self. And these things are far easier to tinker with than you might expect.
Now try and answer these questions:
- Describe how the body-swap illusion is induced.
- How does the Barbie/giant illusion take this a step further?
- What would it mean if simply wearing the video headset changed the way people judged size and distance, as opposed to actually experiencing the body as one's own?
- Why is it important to understand how we perceive ourselves?