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Preferential looking can be used to conclude many things related to an infant’s visual acuity. In preferential looking experiments, a child will be shown two objects, perhaps projected onto a screen, and the experimenter will measure the amount of time a child spends looking at each object.

The results of these experiments will find one of two things. Either the experimenter will observe that the child looks at one object for a significantly greater amount of time the it does the other, or find that both objects are looked at for approximately the same amount of time. The implications of these results are as follows. Should the child be found to look at one object more than the other, then it is reasonable to conclude that the child finds the more observed object more interesting. The important implication of this is that it shows the child is able to distinguish between the two objects. However, should the child spend roughly equal amounts of time looking at each object, then an experimenter could conclude that the child is unable to distinguish between the two objects. Although saying that, it is important to bear in mind that the child may actually be able to distinguish between the two objects, but finds them equally interesting, or indeed, equally boring, therefore one attracts its attention no more than the other.

An example of what preferential looking has shown is that as an infant ages, they are better able to differentiate between a striped black and white pattern and one which is uniformly grey and of the same total luminance. It is presumed that should the child be able to differentiate between the two, it will find the striped pattern more interesting and therefore spend more time looking at it. This was indeed what experiments have shown. However, when premature babies were tested against babies born at term, it was found that the babies born at term were better able to distinguish between the striped pattern and the uniform grey (since they spent a greater proportion of their time looking at the stripes). But then when the age of the infants was measured not from date of birth, but date of conception, it was found that both groups performed to the same level.

Now this can be thought of as a slightly strange result since the premature babies would have had a greater visual experience. What this experiment therefore shows is that environment appears to have little effect on the development of an infant’s visual acuity, at least when it comes to differentiating between a black and white striped pattern and a uniform grey one.

Habituation is based largely on the ideas of preferential looking experiments. It evolved from Fantz’s idea that infants are interested in novelty, so if they become accustomed to a particular stimulus a new stimulus will be preferred as it is more interesting. So, a habituation experiment to determine whether newborn babies can differentiate between various geometric shapes would involve a baby being shown a certain shape until they were bored with it and indifferent to its presence. Then this familiar shape was displayed alongside a new and different shape. The principles of preferential looking apply here. Results show that the babies tested spent a greater proportion of time looking at the new novel shape than the old familiar one. Therefore one can conclude that newborn babies can differentiate between geometric shapes.

It is, however, important to make the point that these newborn babies are not necessarily able to differentiate geometric shapes in the same way adults do. Adults have learned that a three-sided shape is a triangle for example, whereas newborns do not have innately within them the concept of a triangle. From further experiment, it is believed that infants have an in-built system that allows them to detect the differing properties of different shapes. For instance, a newborn may differentiate two shapes based on the total amount of black and white that constitutes them, the size of one shape compared to the other, the varying length of the shapes, or the varying numbers of corners.

The conclusions of preferential looking and habituation experiments all imply that infants have innate systems which allow them to detect information about their surroundings, and also that they have some method of using this information to perceive certain properties of their environment. This then allows them to try and foster some understanding of their environment.

Based on the lectures of Prof. Oliver Braddick, Head of Department of Experimental Psychology, University of Oxford.

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