Psycholinguistics or Linguistics of psychology is the study of the psychological and neurological factors that enable humans to acquire, use and understand language.
While initial forays into Psycholinguistics were largely philosophical ventures, due mainly to a lack of cohesive data on how the human brain functioned, modern biology and neuroscience have spawned a number of subdisciplines, with neurolinguistics and psycholinguistics remaining the two most popular.
Psycholinguistics covers the processes that make it possible to generate a grammatical and meaningful sentence out of vocabulary and grammatical structures, as well as the processes that make it possible to understand utterances, words, sentences, texts etc. Developmental psycholinguistics covers children's learning of language, usually with experimental or at least quantitative methods (as opposed to naturalistic observation like Darwin and Piaget emphasized when studying their own children).
To give an example, one field of research deals with questions like 'How do people learn a second language?' and 'How do children learn their native language?'.
According to Noam Chomsky and like-minded scholars, humans have an innate Universal Grammar (i.e., an abstract concept containing the underpinnings for grammatical rules in all languages). Opponents of this view claim that language is learned only through social contact. However, it is scientifically proven that every healthy human being has the ability to learn many languages, as many as s/he is exposed to for a long enough period of time. This ability reduces considerably after the onset of puberty, so that children can learn any language fairly rapidly wheareas adults may need years to learn a second or third language. It also seems to be the case that the more languages one knows, the easier it is to learn more.
Another aspect of psycholinguistics involves studying individual use of language to understand the mental processes of the individual, a potentially useful tool for psychologists.