Introduction

The human faculty of language is a breathtaking skill. It allows us to communicate observations, thoughts, wishes, intentions, emotions, etc., to another person in the same room (by speaking), to a person in the next room (by shouting), to someone thousands of kilometers away (by speaking on the telephone or sending a fax), and even to future generations (by writing stories, poems, books, or scientific articles). Language is characterized by almost infinite variation and creativity. Every person alive today (with the exception of pre-verbal infants and people with severely impaired language skills) probably utters a number of sentences every day that he or she has never produced before. What other form of behavior could compete with this for degree of novelty and originality?

Language is typically considered to involve a set of interacting, but somewhat separate, domains of ability or knowledge. These include the sound structure of the language (phonology); word meanings (semantics); the ways in which individual morphemes combine to create complex words (morphology); the ways in which morphologically simple or complex words combine to create phrases and sentences (syntax); and finally, at least in the relatively brief time since a substantial proportion of the world's population has become literate, knowledge of how words are written in the speaker's language (orthography).

How and where does the brain represent and process this complex set of abilities? Because language is unique to humans, we can only learn about this topic by studying humans.