Perceptual Learning

Perception is a form of action. It is a skill set that is incredibly useful for gathering information about the environment so that we can act in various ways. Some aspects of our perception are inborn, such as the ability to perceive faces as infants. Others are learned. In this post I want to discuss a famous anthropological case that clearly illustrates the reality of perceptual learning.

In the late 1950s and early 1960s, Colin Turnbull spent time in the Ituri Forest in Congo studying the BaMbuti Pygmies. He spent the majority of his time observing their behavior as it occurred in its natural setting. He had a young(22 years old) Pygmy assistant named Kenge who acted as a guide. On one particular excursion in between villages, Turnbull and Kenge came to the edge of a hill that had been cleared of trees. This clearing offered a view of the distant Ruwenzori Mountains. Normally, the Ituri forest is extremely thick and such clearings are rare. Because of this, Kenge had never experienced a view over such vast distances. He asked if the mountains were hills or clouds. Turnball offered to drive over to the mountain to see them more closely.

On the drive over, it began raining and the visibility was reduced. Upon arriving to the foot of the mountain, Kenge was amazed at their size. He didn’t know what to make of their snowcaps. As they were leaving, a herd of buffalo grazing on the plain a couple of miles away was visible. Kenge asked Turnbull what kind of insects they were! Turnbull tried to inform Kenge that the buffalo were much bigger up close, but because Kenge had never learned the perceptual skill of size constancy, he was skeptical of such claims. Turnbull, of course, drove Kenge to the buffalos. As they were driving, the optic array of the buffalo became larger and larger to Kenge, and he asked Turnbull what sort of witchcraft was at work to make the buffalo grow in size. Over the next day or so, Kenge quickly learned the skill of perceptual size constancy and no longer made such optical errors.

This fascinating anthropological tale vividly illustrates how important exposure to a wide variety of different environments is crucial to developing an adaptable perceptual system. Kenge had grown up in the dense forest and had never been exposed to optical arrays of the environment that offered information about such great distances. This lack of distance information shaped the development of his brain in such a way as to make it quite shocking when he was finally exposed to such optical information 22 years into his life. It is a testament to the plasticity of the brain that he was able to adapt so quickly and illustrates how readily our perceptual systems learn when exposed to new environmental circumstances.