Early language acquisition

Acquisition of language is thought to be a combination of association 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 two objects that look very different, but 20 month old infants are willing to trust the speaker and give two perceptually different objects the same label.

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

In under extension (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 dads blue mini and call all other cars 'trucks'. With experience these errors decrease.