Human Language: Biology, Universals, Development, and Cross-Species Comparisons

Course Logistics & Context

• Remaining schedule
  • Wed: Schizophrenia
  • Fri: Biology of Religion
  • Next Wed (final): Personality Disorders/Individual Differences
  • No dedicated lecture on Depression this year
  • Last two lectures may not be taped

Optimising the Cortex: "Travelling Salesman" in Neural Wiring

• Cortex contains $\approx 2\times10^{10}-3\times10^{10}$ neurons, each making $\sim10^{4}$ synapses
• Depending on wiring efficiency, total axonal length could range from a few km to “$10^{14}$ miles”
• Developmental solution
  • Two‐generation system
  • 1° radial glia set up scaffolding
  • 2° neurons migrate & connect at optimal nodes
  • Swarm intelligence = brain’s analogue of solving travelling-salesman problem (minimise cable length while maximising connectivity)

Universals of Human Language

• Semanticity
  • Continuous acoustic spectrum is chunked into discrete, meaningful units (phonemes → morphemes → words)
  • Discreteness: impossible to utter "$6.5$ words"; you either have a word or you don’t
• Embedded / hierarchical clauses
  • All languages allow A can do B … except under conditions x/y/z
• Recursion / Generativity
  • Finite lexicon → infinite sentences
  • “Bill said that… Jane said that Bill said that …”
• Displacement
  • Ability to discuss past/future, distant places, hypothetical events
• Arbitrariness of sign
  • No intrinsic link between signal & meaning (e.g., “dog” does not look/ sound like a dog)
• Meta-communication
  • Capacity to talk about language (linguistics, dictionaries, language academies, ASL councils)
• Motherese (infant-directed speech/sign)
  • Universal high-pitch, exaggerated intonation, repetition, close eye contact
  • Debate: instructional vs emotional function
  • Similarities to pet-directed speech but with clearer articulation when aimed at babies (goal = teaching)

Language Is Cognitive, Not Merely Motoric

• Evidence from Sign Languages (esp. ASL)
  • Deaf infants “babble” with hands at same age hearing infants babble vocally (esp. before sleep)
  • Strokes in signers → Broca-like or Wernicke-like deficits in signing (not speech)
  • Prosody exists in ASL
  • Facial expression, body shift to mark dialogue, rhythm → conveys tone/ emotion just as vocal prosody does
  • Auditory cortex activates in congenitally deaf signers watching signs ⇒ cortex repurposed for symbolic processing, not sound per se
  • Regional “accents,” slurring & poetry (manual rhyme) in ASL
  • Puns possible (e.g., iconic sign for “milk” → “past-your-eyes milk” = “pasteurised milk”)
  • Second-language storage parallels spoken L2 (same cortical real estate)
  • Even whistle-based language of Canary Islanders maps onto Broca/Wernicke analogues

Neurobiology of Language

• Three canonical cortical areas
  • Broca’s area: inferior frontal gyrus (motor planning → production)
  • Wernicke’s area: posterior superior temporal gyrus (comprehension)
  • Arcuate fasciculus: white-matter tract linking the two (conduction)
• Classic aphasias
  • Broca’s (non-fluent/production): halting speech, intact comprehension
  • Wernicke’s (fluent/receptive): word salad, impaired comprehension
  • Conduction aphasia: intact comprehension & speech but impaired repetition; pure lesions rare
  • Numerous micro-aphasias: alexia (reading loss), agraphia (writing loss), even semaphore aphasia
• Lateralisation
  • $\approx90\%$ of right-handers (and majority of left-handers) = left-hemisphere language
  • Left peri-Sylvian cortex physically thicker
  • WADA test: transiently anaesthetise one hemisphere via carotid → identify language side (being replaced by fMRI)
  • Right hemisphere = prosody, sarcasm, facial & bodily cues; right-side strokes → aprosodia
• Sub-cortical & limbic contributions
  • Basal ganglia: motoric gesturing; people gesture on phone even when unseen; blind speakers gesture
  • Limbic system
  • Enables emotional colouring, music & singing
  • Broca’s patients can sometimes sing what they cannot say (melodic intonation therapy)
  • Tourette’s coprolalia = limbic over-drive bypassing cortical control
• Modularity debate
  • Williams syndrome: eloquent speech despite $\text{IQ}\approx70$ (suggests separability)
  • Specific Language Impairment (SLI): poor language with normal IQ
  • Counter-argument: both cases show broader cognitive anomalies → language not an isolated “Swiss-Army-Knife blade”

Evolutionary Precursors in Primates

• Structural
  • Great-ape & monkey brains show slight leftward enlargement in pre-Broca & auditory cortex
• Functional
  • Vocalisations accompanied by stronger right-side facial expressions (=> left-hemisphere drive)
  • fMRI: species-specific calls preferentially activate left temporal areas
  • Fossil endocasts (Australopithecus) already show asymmetry $\sim1\text{ Myr}$ ago

Development & Acquisition

• Milestones
  • $1{-}3$ mo: equal response to all phonemes; begin preferring speech over non-speech sounds
  • $3{-}6$ mo: statistical learning of syllable co-occurrence; focus on vowels
  • $\approx8$ mo: babbling (signed or spoken); right-face expressivity > left
  • $9{-}12$ mo: lose ability to discriminate unused phonemes; produce language-specific sounds
  • $15{-}20$ mo: first novel combinations = Chomsky’s explosion (proof against strict behaviourism)
  • Vocabulary growth → peaks of $\sim10$ new words/day; adult lexicon $\sim6\times10^{4}$ words
• Neural maturation
  • Gene-expression asymmetry in fetal cortex $\sim12{-}16$ wk gestation
  • Myelination: Wernicke’s precedes Broca’s by $\approx3$ mo (comprehend before speak)
• Critical periods
  • Accent-free mastery rare if L2 starts > $\approx12$ y
  • <$6$ y bilinguals: L1 & L2 share cortical territory; later learners recruit adjacent sites → possible selective aphasia
• Statistical Learning vs Poverty-of-Stimulus
  • Chomsky: innate Universal Grammar; children create rules despite imperfect input
  • Empirical work: infants track transitional probabilities of syllables; can detect violations via heart-rate
• Behaviourism vs Nativism
  • Skinner: operant conditioning (reward correct utterance)
  • Chomsky/Brown: creativity, generativity & rapid growth impossible via reinforcement alone

Social & Cultural Forces

• Peer > Parent influence (Judith Rich Harris)
  • Children adopt community accent, not parents’ (esp. immigrant families)
• Languages encode social values
  • Formal/informal pronouns (tu/vous) shift after revolutions
  • Kin terms tied to interlocutor (Malay lingo: aunt-via-mother vs aunt-via-grandmother)
  • Absolute vs egocentric spatial reference (e.g., “foot to the NW is burning”)
• Sapir–Whorf Hypothesis
  • Language shapes thought; evidence from Amazonian tribes
  • Paraha: number terms = {1, 2, >2}
  • Munduruku: {1–5, >5}
  • Performance normal within lexicon range; chance-level beyond → cognition constrained by available words

Animal Communication: Parallels & Gaps

• Shared features
  • Semanticity: vervet & chicken alarm calls (raptor vs snake; synonymy)
  • Multimodal integration: mismatched face–voice in films startles monkeys
  • Intentionality/theory-of-mind seeds: alarm calls more frequent with kin; suppressed with rivals
• Uniquely (mostly) human
  • Extensive displacement & recursion
  • Arbitrary symbols unlinked to emotion → enables lying
  • Animals’ emotional signals (pheromones, tail position) are involuntary; a frightened dog can only cover scent by tucking tail, not fake confidence

Teaching Apes Human Language – A Cautionary History

• Vocal attempts
  • 1930s “Vicky” forced to say “cup” via operant training → neurotic & failed (laryngeal anatomy inadequate)
  • Kellogg’s chimp “Gua” raised with human infant Donald → Donald began imitating chimp sounds, no language for chimp
• Sign-language era
  • Washoe (Gardners, Nevada)
  • ~150 ASL signs; claimed word invention “water bird” = duck; filmed lying & babbling “tickle me”
  • Sarah (Premack, Penn.)
  • Used magnetic symbols; could handle conditional statements & analogies
  • Coco the gorilla (Patterson, Stanford → Woodside)
  • Publicised as understanding dreams, gossip; notorious anecdote: blamed handler “Bill” for eaten plant
  • Data largely anecdotal; no peer-reviewed corpus
  • Nim Chimpsky (Terrace, Columbia)
  • Intensive analysis showed
    • Random word order; longer utterances ≠ more meaning
    • >95\% responses were trainer-prompted (not spontaneous)
  • Terrace’s 1980 Science paper dismantled previous claims; concluded apes master gestural requests, not language
• Aftermath
  • Patterson vs Terrace feud; promises to return Coco to SF Zoo broken (“has human values”) → legal kerfuffle
  • Field largely collapsed; most evidence deemed wishful interpretation
• Current status – Kanzi (Savage-Rumbaugh)
  • Bonobo using lexigram board & understanding spoken English
  • Demonstrates
  • Spontaneity & comprehension of novel sentences
  • Conditional clauses & analogies
  • Errors stay within semantic category (apple vs orange) – human-like mistake pattern

Key Take-Home Themes

• Biological wiring seeks efficiency; language areas reflect evolutionary & developmental optimisation
• Core universals (semanticity, recursion, displacement, arbitrariness, meta-language) separate human language from animal communication
• Sign-language data prove language is symbolic cognition, not mouth/throat mechanics
• Left-hemisphere specialisation is strong but prosody & emotion recruit right cortex & limbic circuits
• Acquisition is rapid, creative & peer-driven; behaviourist reward alone cannot explain vocabulary explosion
• Thought and language intertwine— sometimes restricting cognition (numeracy in Amazon tribes)
• Attempts to graft human language onto apes underline both shared cognitive substrates and stark limitations (true syntax, spontaneous generativity, unlimited displacement)
• Best evidence of cross-species symbolic competence (Kanzi) still falls short of full‐blown human grammar