Early language acquisition

Acquisition of language is thought to be a combination of associating words to objects or actions along with a social action such as pointing or eye gaze. Gradually children learn to distinguish differences with categories. For example, there is evidence that 16 month olds will not accept a common label for 2 objects that look very different, but 20 month old infants are willing to trust the speaker and give 2 perceptually different objects the same label.

Errors in early word use can help to explain the learning process. 2 errors are overextension and underextension. In overextension, children use a simple word to refer to many different things. For example, an 18 month old may use a word 'doggy' for all animals with 4 legs, or 'daddy' for all adult males. As children's vocabulary increases, their use of overextension decreases.

In underextension, which is less common, children use a single word in a very restrictive way. For example a child may use the word 'car' for just her dad's blue mini and call all other cars 'trucks'. With experience these errors decrease.