Children's sense of having and owning a body differs from that of adults, indicating that our sense of physical self develops over time, according to a new study published in Psychological Science, a journal of the Association for Psychological Science.
Many of our senses -- vision, touch, and body orientation -- come together to inform our perception of having and owning a body. Psychological scientist Dorothy Cowie of Goldsmiths, University of London and colleagues hypothesized that there might be age differences in how these processes come together. To test this hypothesis, they relied on a well-known sensory illusion called the "rubber-hand illusion."
In this illusion, the participant sits with their left hand on a table -- but hidden from view. Instead of looking at her real left hand, she looks at a fake left hand. The experimenter sits across the table and strokes the participant's left hand with a paintbrush while also stroking the fake rubber hand. When the paintbrush strokes are matched so that they occur at the same time and in the same place on the two hands, the participant will often feel as if the fake hand is her own, and perceive the touch she feels as arising from the brush she sees stroking the fake hand.
Cowie and colleagues tested children of three different age groups (4-5; 6-7; and 8-9 years old), as well as adult participants. After experiencing the stroking, the participants were asked to close their eyes and point with their right index finger under the table, so that it was directly underneath the left index finger of their actual hand.
Like adults, children were sensitive to whether the vision and touch cues given by stroking were matched on the real and fake hands. When they were matched, all participants experienced the rubber hand illusion, and when they were asked to point towards their real hand, the points drifted closer to the fake hand and farther away from their own hand.
Interestingly, children of all ages responded more strongly to the illusion than did adults. This shows that children rely more than adults on seeing their body in order to determine their sense of physical self; that reliance on vision created a strong bias toward the fake hand that they were looking at.
These findings indicate that there are two distinct processes underlying the sense of the body that develop according to different timetables -- the process driven by seeing touches on the hand develops early in childhood, while the process driven by seeing a hand in front of us doesn't fully develop until later in childhood.
Co-authors on this research include Tamar Makin of the University of Oxford and Andrew J. Bremner of Goldsmiths, University of London.
This research was supported by a grant from the European Research Council and an award from the Royal Society.
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