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Introduction

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  • Language Has Many Functional Levels: Phonemes, Morphemes, Words, and Sentences

  • Language Acquisition in Children Follows a Universal Pattern

    • The "Universalist" Infant Becomes Linguistically Specialized by Age 1 Year

    • Language Uses the Visual System

    • Prosodic Cues Assist Learning of Words and Sentences

    • Infants Use Transitional Probabilities to Identify Words in Continuous Speech

    • There Is a Critical Period for Language Learning

    • "Motherese" Enhances Language Learning

  • Several Cortical Regions Are Involved in Language Processing

    • Language Circuits in the Brain Were First Identified in Studies of Aphasia

    • The Left Hemisphere Is Specialized for Phonetic, Word, and Sentence Processing

    • Prosody Engages Both Right and Left Hemispheres Depending on the Information Conveyed

    • Language Processing in Bilinguals Depends on Age of Acquisition and Language Use

    • The Model for the Neural Basis of Language Is Changing

  • Brain Injuries Responsible for the Aphasias Provide Important Insights into Language Processing

    • Broca Aphasia Results from a Large Lesion in the Left Frontal Lobe

    • Wernicke Aphasia Results from Damage to Left Posterior Temporal Lobe Structures

    • Conduction Aphasia Results from Damage to a Specific Sector of Posterior Language Areas

    • Global Aphasia Results from Widespread Damage to Several Language Centers

    • Transcortical Aphasias Result from Damage to Areas Near Broca's and Wernicke's Areas

    • The Classical Aphasias Have Not Implicated All Brain Areas Important for Language

  • An Overall View

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Language is uniquely human and arguably our greatest skill and our highest achievement. Despite its complexity, all typically developing children master it by the age of three. What causes this universal developmental phenomenon, and why are children so much better at acquiring a new language than adults? Once language is mastered, what brain systems are involved in language processing, and how does brain damage produce the various disorders of language known as the aphasias?

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For centuries these questions about language and the brain have prompted vigorous debate among theorists. In the last decade, however, an explosion of information regarding language has taken us beyond the nature–nurture debates and beyond the standard view of specialized brain areas responsible for language. Two factors are largely responsible for this change.

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First, functional brain imaging techniques such as positron emission tomography (PET), functional magnetic resonance imaging (fMRI), electroencephalography, and magnetoencephalography have allowed us to examine activation patterns in the brain while the subject carries out language tasks—naming objects or actions, listening to sounds or words, or detecting grammatical anomalies. The results of these studies reveal a far more complex picture than the one first conceived of by Carl Wernicke in 1874, a picture in which multiple and relatively segregated brain systems cooperate functionally in language processing.

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Second, behavioral and brain studies of language acquisition show that infants learn language in ways that had not been envisioned. Well before children produce their first words, they learn the sound patterns underlying the phonetic units, words, and phrase structure of the language they hear. Listening to language alters the infant brain early in development, ...

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