Language and Speech: Neuroscience, Theories, and Disorders

Phoneme

The smallest unit of sound that can change word meaning.

Morpheme

The smallest meaningful unit of a word (e.g., un- in undo).

Lexicon

The mental 'dictionary' that stores word forms and associated information.

Prosody

Tone, pitch, and rhythm of speech.

Syntax

The rules governing admissible combinations of words in phrases and sentences.

Morpheme in ASL

The smallest meaningful movement.

Formants

Resonance peaks shaped by the vocal tract.

FOXP2 mutation

Associated primarily with deficits in sequencing articulation patterns.

FOXP2 gene

A transcription factor regulating many other genes.

Discontinuity theories of language evolution

Propose that language emerged rapidly and recently in modern humans.

Continuity theories

Emphasize that language developed from modifications of existing animal communication systems.

MacNeilage's proposal

Focuses MOST on articulation and mouth movements.

Alex the African gray parrot

Demonstrated particularly strong ability to categorize and label objects by color, shape, and material.

Washoe the chimp

Primarily communicated using American Sign Language (ASL) signs.

Sarah, Premack's chimp

Learned a communication system using lexigrams on a keyboard.

Lana and Yerkish

Trained to use Yerkish, which is a language based on lexigrams on a computer keyboard.

Kanzi's performance

Important because he learned Yerkish lexigrams spontaneously by observation.

Wernicke-Geschwind model

Proposes that comprehension is extracted in Wernicke's area and then passed via the arcuate fasciculus to Broca's area for speech production.

Key limitation of the Wernicke-Geschwind model

Treats language as restricted to a few small cortical regions.

Dorsal language stream

Most strongly involved in mapping sound to articulation (phonology → motor).

Ventral language stream

Primarily associated with semantic processing (sound → meaning).

Patient with intact dorsal, impaired ventral pathway

Can repeat nonsense syllables but does not understand their meaning.

TMS to anterior Broca's area

Primarily disrupts phonological processing.

TMS to posterior Broca's area

Primarily disrupts phonological (sound-based) decisions.

Penfield's electrical stimulation of speech zones

Commonly produced speech arrest, hesitations, and naming errors.

Semantic network identified by Binder and colleagues

Includes the angular gyrus, which is MOST associated with integration and retrieval of complex conceptual knowledge.

Brain dictionary

Based on lesion-symptom overlap across stroke patients.

Semantic maps in the brain dictionary work

Found in multiple regions of both hemispheres.

Aphasia

Characterized as a language disturbance due to brain injury.

Paraphasia

Involves unintended syllables or words with correct articulation.

Wernicke (sensory) aphasia

Most strongly associated with poor comprehension and fluent 'word salad' speech.

Conduction aphasia

A patient who speaks fluently, understands speech, but cannot repeat sentences likely has this condition.

Anomic (amnesic) aphasia

Defined chiefly by difficulty finding object names despite fluent, meaningful speech.

Nonfluent (Broca) aphasia

Characterized by effortful, telegraphic speech with relatively preserved comprehension.

Wernicke aphasia

Marked by fluent but meaningless speech.

Alexia

Refers to the inability to read.

Word deafness

Most specifically refers to the inability to comprehend spoken words despite normal hearing for other sounds.

Middle cerebral artery (MCA)

Important for aphasia because it supplies blood to much of the left perisylvian language cortex.

Chronic apraxia of speech

Most closely linked to lesions of the insula.

Recurring stereotyped utterances

Associated with damage to the arcuate fasciculus.

Thalamic contributions to language

Thought to involve activation and arousal of cortical language regions.

Right-hemisphere lesions

Most likely to produce deficits in prosody, metaphor comprehension, and discourse coherence.

Right hemisphere contributions

Shows relatively stronger contributions to emotional tone and global discourse.

Token Test

A comprehensive aphasia battery.

Boston Diagnostic Aphasia Test

Primarily used as a brief aphasia screening tool.

Deep dyslexia

Most strongly characterized by semantic reading errors and inability to read nonwords.

Phonological dyslexia

Defined by the inability to read nonwords aloud.

Surface dyslexia

Most evident when the person misreads irregular words by applying regular letter-sound rules.

Dual-route theory of reading

Proposes that reading uses both lexical (whole-word) and nonlexical (letter-sound) routes.

core language skills

categorizing, category labeling, sequencing behaviors, and mimicry