Through the eyes of a child
The way in which children and adults process visual information indicates that they perceive the world quite differently, shows new research from the UK. The study, presented in the Proceedings of the National Academy of Sciences (PNAS) journal, concludes that children up to the age of 12 do not combine sensory information the way adults do. The research was conducted by scientists from University College London (UCL) and the University of London's Birkbeck College in the UK. Lead author Dr Marko Nardini of UCL's Institute of Ophthalmology explains: 'To make sense of the world we rely on many different kinds of information. A benefit of combining information across different senses is that we can determine what is out there more accurately than by using any single sense.' This also applies to different types of input within a single sense. 'Within vision,' says Dr Nardini, 'there are several ways to perceive depth. In a normal film, depth is apparent from perspective, for example in an image of a long corridor. This kind of depth can be seen even with one eye shut. In a 3D [three-dimensional] film, and in real life, there is also binocular depth information given by differences between the two eyes.' This integration of sensory information is a useful skill, which helps to reduce uncertainty in our interpretation of our surroundings. It is not, however, an ability with which we are born. Focusing specifically on visual information, Dr Nardini and his colleagues analysed how children and adults combine perspective and binocular depth perception. In a first experiment, children and adults wearing 3D glasses were asked to compare two slanted surfaces based on separate perspective and binocular information, or both, and to decide which was the flattest. Adults tended to reply with greater accuracy using a blend of both sets of input. The researchers observed that the ability to use both types of depth information simultaneously only develops around the age of 12. Professor Denis Mareschal, from the Centre for Brain and Cognitive Development at Birkbeck, is one of the co-authors of the study. He notes that 'Babies have to learn how different senses relate to each other and to the outside world. While children are still developing, the brain must determine the relationships between different kinds of sensory information to know which kinds go together and how. It may be adaptive for children not to integrate information while they are still learning such relationships - those between vision and sound, or between perspective and binocular visual cues.' And indeed, the ability to combine the pieces of the sensory puzzle can come at a cost. Adults can lose the knack for separating the individual items of information that combine into the bigger picture, particularly within a single sense. This phenomenon is known as 'sensory fusion'. Another experiment conducted by the team involved special 3D disks where perspective and binocular information sometimes disagreed. In these tests, six-year-olds outperformed adults in spotting differences in the slant of the disks. So it seems that children do, indeed, see the world quite differently. The team is planning to conduct further research involving functional magnetic resonance imaging (fMRI) to analyse the brain changes that arise as children develop the ability to combine visual information.
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