Chapter 20: Language

Language - a system by which sounds, symbols, and gestures are used for communication

• Language comes into our brains through the visual and auditory systems, and we produce speech and writing with our motor system

• Brain processing between the sensory and motor systems is the essence of language

• Not all communication is language (dog growls, bee waggle dances, vervet monkey calls)

• Language involves the ability to use syntax (rules for grammar) to create new meanings

What is Language?

• Speech - an audible form of communication built on the sounds humans produce

• Human Sound:

  • Exhale air out of the lungs → larynx(voice box) → pharynx → mouth (tongue, jaw, lips) → nose

    • Adam’s apple is the larynx’s anterior wall of cartilage

    • Vocal folds and vocal chords form a “v” in the larynx

      • Sounds are produced in the glottis, space between the tightened vocal folds, via vibrations

      • Pitch is a result of frequency of vocal fold vibrations (greater tension, higher frequency)

  • Phonemes - the fundamental sounds that a language uses to communicate

    • 44 in English

• Experiments with chimps and speaking human language have been unsuccessful as their vocal tracts are not structured to make the sounds humans make

  • There is evidence that chimps make gestures with the intention of influencing the behavior of other animals

  • Non-human primates can also understand the meaning of gestures and symbols as well as phrases in human language

• Language acquisition - learning a language

  • Infants discriminate words (eliminating the segmentation problem) by statistical learning (how likely a sound is going to follow or lead another) and syllable emphasis (stress on the first syllable in English)

    • Prosody (tone) is understood early on

• Genetics play an important role in the susceptibility to language disorders

  • In a British family, known as KE, of three generations, about half had verbal dyspraxia, an inability to produce the coordinate muscular movements needed for speech

    • Their speech was unintelligible to both the general public and family members

    • The affected individuals had difficulties with grammar, language, and had lower IQs than other family members

    • Affected individuals has structural abnormalities in the motor cortex, cerebellum, and striatum (caudate and putamen)

    • A mutation of a single gene (FOXP2) affected the development of the motor cortex, cerebellum, and striatum

• A growing number of genes have been identified that are potentially involved in common language disorders

  • Specific language impairment (SLI) - developmental delay in the mastery of language that is not associated with hearing difficulty or more general developmental delays

    • More than 50% of children with SLI have a parent or sibling with the condition

      • concordance rate in identical twins

    • CNTNAP2 and KIAA0319 have been identified as other genes that code for normal language acquisition

  • Dyslexia - a difficulty learning to read despite normal intelligence and training

    • Has a strong genetic link

    • The KIAA0319 gene is associated with dyslexia as well as SLI

      • Dyslexia is often found in individuals with SLI

    • Results from normal patterns of neocortical development

The Discovery of Specialized Language Areas in the Brain

• Aphasia - the partial or complete loss of language abilities following brain damage

  • Often without the loss of cognitive faculties or the ability to move muscles used in speech

• Broca proposed that language expression is controlled by only one hemisphere, almost always the left

  • The Wada procedure of a single hemisphere of the brain being anesthetized supported Broca’s view

    • Injecting one side of the carotid artery with amobarbital

      • Targeting left side decreases conscious language-based memory

      • Targeting right side does not decrease language

    • fMRI has replaced this technique

  • Almost all right-handed people have a left hemisphere dominance for language

  • Broca’s Area - the region of the dominant left frontal lobe that Broca identified as critical for articulate speech

  • Leborgne could not communicate past the word “tone”

    • Broca identified a lesion in the left frontal lobe

• Wernicke’s Area - the region located on the superior surface of the temporal lobe between the auditory cortex and the angular gyrus

  • Responsible for language comprehension

  • Lesions can disrupt normal speech and sound recognition deficiencies

Language Insights from the Study of Aphasia

• Broca’s Aphasia - motor aphasia, in which the individual has difficulty speaking even though they understand language heard or read

  • People with Broca’s aphasia have difficulty saying anything, often pausing to search for the right word (telegraphic speech)

  • Anomia - the inability to find words

  • Speech includes mainly content words (nouns, verbs, and adjectives, but few function words (articles, pronouns, and conjunctions)

    • Agrammatism - the inability to construct grammatically correct sentences

      • Affects complicated grammar

    • Paraphasic errors - substituting incorrect sounds or words (“purnpike” for “turnpike”)

  • More complex questions with more function words are harder to understand

• Wernicke’s Aphasia - speech is fluent but comprehension is poor

  • Make more paraphasic errors and use incorrect words (sometimes with the correct sounds “click” instead of “pick”)

  • Are unable to comprehend questions understood by Broca aphasics

  • Strange speech patterns (spoken, written, sung)

    • Problems with playing songs on instruments

• Wernicke-Geschwind Model - a model for language processing in the brain

  • Includes Broca’s area, Wernicke’s area, the arcuate fasciculus, and the angular gyrus

  • Repetition of Spoken Words: Auditory cortex → Wernicke’s area → arcuate fasciculus → Broca’s area → motor cortex

  • Reading Written Text Aloud: primary visual cortex → angular gyrus → Wernicke’s area → Broca’s area → motor cortex

  • Model is an oversimplification of the actual pathways involved in speech and understanding language

  • Current Model of Language Processing: Broca’s area → ← auditory cortex; Broca’s area → ← Wernicke’s area; premotor cortex → ← Wernicke’s area

• Conduction Aphasia - aphasia from a disconnection lesion

  • Difficulty in repeating words (especially function words, polysyllabic words, or nonsense sounds)

  • Comprehension of sentences read aloud

    • Deficit between the regions involved in comprehension and speech

• Following a stroke, aphasia in bilingual people may affect the later learned language more than the one learned earlier in childhood

• Aphasia in people who primarily communicate via sign language causes impairment in “speech” through gestures, though comprehension is unaffected (similar to Broca’s aphasia)

  • Impairment similar to Wernicke’s aphasia (making mistakes with gestures and difficulty comprehending other signing) can occur

Asymmetrical Language Processing in the Two Cerebral Hemispheres

• Split-Brain Studies - studies in which the hemispheres are surgically disconnected (along the corpus callosum)

  • Produces the most valuable and fascinating findings on the language differences of the two hemispheres

  • The visual field and motor system are contralateral, so the right visual field and right hand are controlled by the left hemisphere and vise versa

• Commissures - several bundles of axons where communication between the cerebral hemispheres occurs

  • Corpus callosum is the largest of the commissures

• Roger Sperry performed split brain studies in animals

  • Cutting the corpus callosum in a cat or monkey has no noticeable effect on the animal’s behavior

  • Animals sometimes acted as if they had two separate brains both competing to recognize the same stimuli

• Surgeons used the knowledge of split-brain procedures resulting in no major deficits to treat severe epilepsy (as a last resort)

• Studying split-brain involves careful control to present stimuli to only one cerebral hemisphere

  • Gazzaniga used a device with a camera-like shutter to flash an image to both eyes, yet only one cerebral hemisphere “sees” the stimulus

    • Presented the images a shorter time than a saccadic eye movement to focus the image on the fovea or process through the entire visual field

  • In split-brain patients, the left visual field and left hand does not recognize stimuli, as the left hemisphere controls speech in most people

  • The right hemisphere is able to understand numbers, letters, and short words

    • Writing is also significant to this hemisphere

  • These studies demonstrates the brain’s ability to function as independent brains with different language abilities

    • Ex) 1: heart; 2: smiley; 3: smiley

• Asymmetry of the hemispheres has important functions

  • Planum Temporale - region a part of Wernicke’s area on the superior surface of the temporal lobe

    • In most brain’s the left planum temporale is larger than the right

      • Points to speech becoming dominant in the left hemisphere because of pre-existing size difference

      • Broca’s area and the insula are also larger in the left hemisphere

  • The correlation is not strong enough to allow one to predict the language-dominant hemisphere from anatomical measurements alone

    • Insula - the cerebral cortex within the lateral sulcus that is between the temporal and parietal lobes

      • Best predicts which hemisphere is dominant for language

      • Its role in language is unknown

Language Studies Using Brain Stimulation and Human Brain Imaging

• Aspects of language processing have been revealed by electrical brain stimulation and brain imaging with fMRI and PET in living humans

• Penfield noted that stimulation at certain locations resulted in three main categories of speech effects: vocalizations, speech arrest, and speech difficulties similar to aphasia

  • Stimulation of motor cortex in the area that controls the mouth and lips caused immediate speech arrest

  • Stimulation of motor cortex on either side of the brain occasionally evoked cries or rhythmic vocalizations

  • Stimulation of an area that appeared to correspond to Broca’s area resulted in aphasia and anomia

• Areas involves in language are more extensive than simply Broca’s and Wernicke’s areas, as they have been found to include other cortical areas as well as parts of the thalamus and striatum

• With PET and fMRI, the level of neural activity in different parts of the brain is inferred form regional blood flow

  • Significant bilateral activation is commonly observed in fMRI studies associated with language

  • PET of subjects seeing words or hearing words revealed that areas activated in the extrastriate cortex (visual) and secondary auditory cortex did not respond to visual and auditory stimuli that were not words

  • PET of subjects repeating words showed high bilateral activity in primary motor cortex, the supplementary motor area, and around the Sylvian fissure near Broca’s area

  • PET of subjects doing noun-verb association tasks showed high activity in the left inferior frontal area, anterior cingulate gyrus, and the posterior temporal lobe

  • Evidence from numerous PET and fMRI studies that distributed and distinct brain areas store info about different categories of objects