Form perception
In the American Indian language Navaho, the form of a verb for handling an object varies with the form or shape of the object. For instance, if one asks somebody to hand over an object, the form of the verb will vary according to whether the object is long and flexible like a piece of string, long and rigid like a stick, or flat and flexiblelike paper or cloth. In general, Navaho-speaking children use these verb forms correctly as early as the age of three. Thus, the grammar of Navaho classifies objects according to form or shape in a way that English grammar does not.
In an experiment, Navaho children from the same reservation and living under similar circumstances were divided into two groups according to whether English or Navaho was their dominant language. Both groups were given pairs of objects where each object differed from the other in two respects, such as colour and size, colour and shape/form, or size and shape/form. For instance, one of the pairs consisted of a yellow stick and a piece of blue rope of comparable size, differing from each other in both colour and shape/form: