Lecture 23: Language

What this lecture covers

This lecture asks what makes human language distinctive and how it arises from biology, moving from universal features of language across roughly 6,000 human languages through the neurobiology of production and comprehension, into how children acquire language, and finally into what animals can and cannot do with communication. It continues the course's pattern of starting from behavior and working back to the underlying biology.

After watching, you should be able to list the universal properties of human language, describe the roles of Broca's area, Wernicke's area and the arcuate fasciculus, explain why the Chomsky-Skinner debate turned on children generating novel sentences, and evaluate why most chimp and gorilla "language" projects failed a rigorous scientific test while one bonobo project held up better.

Key ideas

• Semanticity: language breaks the infinite range of possible sounds into discrete units of meaning; you can't say "6.5 words."
• Recursion and displacement: language can embed clauses within clauses to generate infinite sentences from finite words, and can refer to things distant in time, place or emotion, unlike most animal signals.
• Arbitrariness: the sound of a word bears no necessary relationship to its meaning, which is also what allows language to be used for deception.
• Language is cognitive, not just motoric: evidence from American Sign Language, such as babbling in signs, sign-language aphasias, and auditory cortex activation in deaf signers, shows language is about abstract structure, not lips and ears.
• Lateralization: language is left-hemisphere dominant in about 90% of people, with Broca's area handling production, Wernicke's area handling comprehension, and the arcuate fasciculus connecting the two; damage to each produces a distinct type of aphasia.
• Poverty of stimulus: children generate word combinations they have never heard (Chomsky's core evidence against a purely behaviorist account of language learning), though statistical learning also plays a real role.
• Critical periods: a second language learned before about age six shares brain regions with the first language; learned later, it activates more peripheral regions, and accents from languages learned after about age twelve tend to be permanent.
• Language shapes thought: number-word-poor Amazonian tribes (the Piraha and Munduruku) show reduced numerical precision above their small vocabulary of number terms, offering support for a Sapir-Whorf-style effect of language on cognition.

Walkthrough

Universals of human language (2:05)

The lecture opens with features shared across all human languages: semanticity, embedded clauses, recursion (a finite vocabulary generating infinite sentences), displacement from the immediate and emotional, arbitrariness of sound-to-meaning mapping, metacommunication (the ability to discuss language itself), and motherese. American Sign Language is used throughout to argue that language is fundamentally about cognitive structure rather than the mechanics of speaking and hearing: deaf infants babble in sign on the same developmental timeline as hearing infants, ASL has prosody, accents, puns and poetry, and signing activates the auditory cortex in people born deaf.

Brain regions for language (14:17)

The lecture works through the debate over how modular language is in the brain, using Williams syndrome (fluent language, low IQ) and specific language impairment (poor language, normal IQ) as competing evidence, before concluding the strict-module view is weak. It then maps the three key regions: Broca's area (motor cortex adjacent, governing language production; damage causes halting Broca's aphasia), Wernicke's area (near auditory cortex, governing comprehension; damage causes fluent but meaningless "word salad"), and the arcuate fasciculus connecting them, whose damage would in principle prevent converting comprehension into production. Lateralization is demonstrated through stroke studies and the Wada test, which anesthetizes one hemisphere at a time to locate language function before epilepsy surgery.

Emotion, gesture and the limbic system (31:26)

Language production draws on the basal ganglia for motor output and is deeply intertwined with the limbic system, evidenced by involuntary hand gestures during phone calls (even among blind speakers), by patients with Broca's aphasia who can sing words they cannot say, by the cursing seen in Tourette's syndrome, and by psychotherapy's basic premise that talking changes emotional states. Prosody, the tone, facial expression and gesture that accompany words, is largely right-hemisphere.

Development and acquisition (40:34)

The Skinner-Chomsky debate is presented as resolved largely in Chomsky's favor: children reliably produce sentence constructions they have never heard, which behaviorist reward-and-punishment learning cannot explain, though later research shows infants as young as six months can also pick up statistical patterns in artificial language streams. The lecture traces developmental landmarks from broad phoneme sensitivity in early infancy, through narrowing to the native language's sounds, babbling around eight to nine months, to the first spontaneous novel combinations around 15 to 20 months. New languages, the lecture argues, are invented and reshaped by children, illustrated by the emergence of Nicaraguan Sign Language among deaf schoolchildren over roughly three generations.

Language, culture and thought (1:00:51)

Peer influence, not parental influence, shapes accent and language style, which the lecture ties to Judith Rich Harris's broader argument about peer socialization. Cross-linguistic examples, such as formal and informal pronouns, kinship terms that must specify the listener's relationship, and non-egocentric direction systems based on cardinal points rather than the speaker's body, are used to introduce the Sapir-Whorf hypothesis that language constrains thought. The Piraha and Munduruku number-word studies are presented as strong recent evidence: both groups perform accurately with small quantities but lose precision above the limits of their number vocabulary, despite being expert in other complex domains like edible plants.

Animal communication and the failure of ape language projects (1:12:00)

Animal communication shares some building blocks with human language, including semanticity in vervet monkey alarm calls, multimodal integration of vocalization and facial expression, and intentional, audience-sensitive signaling. What remains distinctively human is displacement, arbitrariness and the capacity to lie, illustrated by contrasting a person's ability to mask fear in words with a dog's inability to suppress its stress pheromones. The lecture then recounts the history of ape language projects, from the failed attempts to teach chimps Vicki and Donald to speak, through the sign-language chimps Washoe and Nim Chimsky and the gorilla Koko, to Herb Terrace's 1979 analysis showing none of them met basic criteria for language (spontaneity, proper word order, added meaning with longer utterances). The bonobo Kanzi is presented as the one case with more credible evidence of language-like ability, including working analogies and semantically related errors.

Before you watch

• Review the earlier lecture on vervet monkey alarm calls and animal communication, since this lecture builds directly on it.
• Basic familiarity with brain lateralization and cortical anatomy will help with the neurobiology sections.
• No specific prior linguistics knowledge is assumed.

Check your understanding

1. What evidence from American Sign Language supports the claim that language is fundamentally cognitive rather than motoric?
2. How do Broca's aphasia and Wernicke's aphasia differ in their effect on production versus comprehension?
3. Why did children's novel word combinations pose a problem for the behaviorist account of language acquisition?
4. What did Herb Terrace's analysis find was missing from Nim Chimsky's, Washoe's and Koko's sign-language use?
5. How do the Piraha and Munduruku number systems provide evidence for the Sapir-Whorf hypothesis?