Neurolinguistics LING 400 Winter 2010

Overview Vocal tract specialization for language Brain specialization for language Innateness Hypothesis for further learning: LING/PSYCH 347 (Psychology of Language I), or SPHSC 425 or 445 please turn off your cell phone

Human language seems unique among animal communication systems Chimps can learn some aspects of human language −Show some spontaneity, creativity −Skills comparable to 1-2 year old child …but −Don’t get better than 1-2 year old child −Limited syntax

Human vocal tract shows specialization for speech Adult human vocal tract Chimp vocal tract

Human brain also shows specialization for language Some brain areas seem to be “dedicated” to language processing

The Localization Hypothesis Different brain areas are responsible for different functions −Most people have same basic “wiring scheme” −Damage to a brain area impairs functions handled by that area −Direct electrical stimulation of different brain areas  distinct responses (twitches, numbness, hallucinations, transient impairments) −Stimulation of “language areas” can cause vocalizations or difficulty speaking

TOP VIEW Basic Brain Anatomy Left and right hemispheres divided by longitudinal fissure Corpus callosum (not shown) −bundle of nerve fibers that allows information to pass between hemispheres

Basic Division of Cortical Functions Outer cortex divided into lobes separated by fissures (sulci [ | s ʌ lsa ɪ ], singular sulcus [ | s ʌ lk ə s]) −Temporal lobe: primary auditory processing, long-term memory −Occipital lobe: primary visual processing −Parietal lobe: high-level visual processing, sensory integration & synthesis (spatial awareness) −Frontal lobe: primary motor control, planning, decision-making SIDE VIEW

Primary Language Processing Areas Broca’s Area −primarily involved in language production −adjacent to motor cortex Wernicke’s Area −primarily involved with language comprehension −adjacent to primary auditory cortex (pink and bigger) Arcuate fasiculus (not shown) −nerve fibers that connect Wernicke’s & Broca’s areas Angular Gyrus −plays a role in understanding metaphor

Language Deficits: Broca’s Aphasia non-fluent, telegraphic speech basic meaning usually clear, good comprehension some pronunciation errors A Broca’s aphasic tells the story of Cinderella −Cinderella... poor... um ’dopted her... scrubbed floor, um, tidy... poor, um...’dopted... si-sisters and mother... ball. Ball, prince um... shoe.

Language Deficits: Wernicke’s Aphasia fluent production, but nonsensical poor comprehension A Wernicke’s aphasic describes a knife −That’s a resh. Sometimes I get one around here that I can cut a couple regs. There’s no rugs around here and nothing cut right. But that’s a rug and I had some nice rekebz. I wish I had one now. Say how Wishi idaw, uh windy, look how windy. It’s really window isn’t it?

Lateralization = Difference in Function Between Hemispheres Right Hemisphere: “holistic” processing −pattern-matching (e.g., recognizing faces), spatial relations, emotional reactions, music (in musically naïve individuals) Left hemisphere: “analytical” processing −mathematics, logical reasoning, temporal relations, rhythm, music (in musically sophisticated individuals) Language processed by left hemisphere for most people

Contra-Lateral Control In general, right side of brain processes information and controls movement for left side of body, and vice versa Some exceptions, including −speech sounds processed by left auditory cortex (Wernicke’s area) (including sound from left ear); non- speech sounds usually processed by right auditory cortex

Evidence for Left-Lateralization of Language Processing Aphasia −Most aphasias result from left hemisphere damage ‘Split brain’ patients −Corpus callosum severed (e.g. to control severe seizure disorders like epilepsy) −Marked performance difference on language tasks involving left vs. right sides −E.g. naming object −left eye open (right brain), right eye covered much harder than (or impossible) −right eye open (left brain), left eye covered

Evidence for Left-Lateralization of Language Processing Dichotic listening tasks −If speech sounds heard by only one ear, processed faster and more accurately when heard by right ear (left brain) −Non-speech sounds processed faster and more accurately through left ear Tone (pitch) −Speakers of tonal languages (e.g., Thai) process linguistic tone in left hemisphere −Speakers of non-tonal languages (e.g. English) process tone in right hemisphere

What About Signed Languages? Signers, like speakers, tend towards left-lateralization Aphasias are similar −Wernicke’s: difficulty recognizing single signs, following commands, and understanding sentences; sign selection errors −Broca’s: sign production impairment (“halting and effortful”), but comprehension OK

Right Hemisphere Damage in Native Signers Non-aphasic problems such as left hemispatial neglect −When describing furniture in a room: “furniture piled in helter-skelter fashion on the right, and the entire left side of the signing space left bare...” −Describing the Cookie Theft Picture: girl ignored

Summary Human brain shows some specialization for language Caveats re localization and lateralization

Against Localization For complex cognitive tasks, processing more diffuse than specific areas Functions lost due to permanent injury can be recovered (to a certain extent) by “recruiting” new areas to perform function of damaged area Non-localized neurological decay (e.g. Alzheimer’s disease) can also cause language deficits (among other problems) Functions of areas not entirely specialized −Localized damage to “language areas” sometimes causes motor control problems and cognitive/perceptual deficits

Against Left-Lateralization of Language Right-hemisphere damage can cause language deficits, even in people who appear to be “left-lateralized,” affecting −prosody (emotion, tone of voice) −discourse (jokes and puns; reference to things said in previous sentences) −pragmatics

Lateralization Statistics: Handedness Likelihood of left-lateralization increases if: −adult / male / right-handed / literate / monolingual ≈ 90% of humans right-hand dominant −≈ 90% of these left-lateralized for language −the rest almost all right-lateralized ≈ 10% of humans left-hand dominant or ambidextrous −≈ 65% of these left-lateralized for language −the rest either right-lateralized or bilateral

Lateralization Statistics: Gender and literacy Left-lateralization seems to be less strong in women −Left hemisphere damage in women less likely to result in aphasia −Aphasia from left hemisphere damage tends to be milder −Dichotic listening tests don’t show right ear advantage as often Illiterate speakers −Language processing tends to be more bilateral −Aphasias can result from damage to either hemisphere

The Innateness Hypothesis Humans “genetically programmed” for language...language appears to be a true species property, unique to the human species in its essentials and a common part of our shared biological endowment, with little variation among humans... — Noam Chomsky

Universal Grammar (UG) There are universal properties of human languages. UG determines possible forms of human language Why would UG exist? −Maybe UG is innate knowledge hard wired into brain −Or maybe UG a consequence of structural properties that are common to all (normal) human brains