Source: Laboratories of Nicholaus Noles and Judith Danovitch—University of Louisville

It might be possible for the human brain to keep track of each individual person, place, or thing encountered, but that would be a very inefficient use of time and cognitive resources. Instead, humans develop categories. Categories are mental representations of real things that can be used for a variety of purposes. For example, individuals can use the perceptual features of animals to place them into a given category. So, upon seeing a furry, four-legged, tail-wagging, barking animal, a person can determine that it is a dog. This is one of many examples where people use perceptual similarity to fit new experiences into their existing mental representations.

However, category membership is much more than skin deep, especially for representations of animals. Frank Keil demonstrated this by using a simple, yet powerful technique that focused on the differences between natural kinds and artifacts. Natural kinds include animals and other living things, while artifacts consist largely of nonliving things, such as tables or gold bricks. In his study, Keil told children stories about natural kinds and artifacts that underwent transformations causing them to cross categorical boundaries. For example, he described a step-by-step process by which a raccoon was transformed into a creature that resembled a skunk in every way. At the end of the story, the raccoon was black with a white stripe, and it had implanted glands that made it smell like a skunk, too. He asked the children to determine whether the resulting animal was a raccoon or a skunk. He used a similar method to describe the transformation of a tire-an artifact-into a shoe. Children's responses revealed interesting developmental changes into how people think about artifacts and natural kinds.

This video demonstrates Frank Keil's transformation study.¹

Recruit healthy 5-, 7-, and 9-year-old children with normal hearing and vision and no history of developmental disorders. For the purposes of this demonstration, only one child is tested. Larger sample sizes (as in Frank Keil's transformation study¹) are recommended when conducting any experiments.

1. Data collection

1. Gather the necessary materials.
   1. Design eight vignettes describing the transformation of animals from one kind to another via surgery.

In order to have enough power to see significant results, researchers would have to test at least 18 children in each age group. Typically, when asked about artifacts, children in all three age groups conclude that what is seen confirms the categorical placement. If a tire is transformed into a rubber shoe, then it is a shoe and not a tire. In contrast, children presented with natural kinds reveal a developmental trend. Five-year-olds are either indecisive or see an animal's posttransform

Frank Keil's work demonstrates that internal characteristics count. Children treat category membership as springing from internal characteristics that cause animals' appearances and behaviors, and children continue to have the intuition that animals belong to their category, even when appearances and behaviors change. Generally, this finding supports other work demonstrating that children use categorical information and not other cues, such as appearance, to guide their inferences about animals. For example, indi

1. Keil, F.C. Concepts, Kinds, and Cognitive Development. MIT Press: Cambridge, MA (1989).