Language Processing: Split-Brain & EEG

Phonology Clarifications

• Split-brain involves the brain's lateralization and its ability to compensate for damage.
• Different frequency bands (delta, theta, beta, gamma) have various roles in language processing.
• Kids with aphasia tend to recover better than adults.
• There is a bioprogram hypothesis.

Split Brain Experiments

• Experiments with split-brain patients help illuminate the lateralized nature of brain function.
• Split-brain patients undergo surgery to cut the corpus callosum, which connects the two sides of the brain.
• Visual information from the left field of view is processed by the right hemisphere, and vice versa.
• A word flashed to the right field of view is verbally identified by the patient because the left hemisphere is dominant for verbal processing.
• A word flashed to the left field of view cannot be verbally identified, because the right hemisphere cannot share information with the left, but the patient can draw it.

EEG Bands

Delta (0.5-4 Hz)

• Associated with deep sleep, unconscious states, and slow-wave cognitive processes.
• Less directly associated with speech processing in awake individuals but can be observed in studies with sleep.

Theta (4-8 Hz)

• Associated with drowsiness, light sleep, meditation, and memory retrieval.
• Linked to memory encoding and retrieval, crucial for language comprehension and speech production; plays a role in semantic processing and contextual information integration.

Alpha (8-12 Hz)

• Associated with relaxation, calmness, and a wakeful state.
• Observed when individuals are in a relaxed state but not actively processing language; changes in alpha activity can indicate shifts in attention and cognitive workload during speech tasks.

Beta (12-30 Hz)

• Associated with active thinking, focus, problem-solving, and motor control.
• Prominent during active speech processing, including language comprehension, speech production, and auditory processing, often linked to motor planning for speech articulation and cognitive load for complex linguistic tasks.

Gamma (30-100 Hz)

• Associated with high-level information processing, perception, and consciousness.
• Crucial for higher-level cognitive functions, including sensory input integration during speech perception and synchronization of neural networks in language comprehension and production; also associated with the binding of phonological and semantic information during speech.

Theta Example

• Syllables organize sequences of speech sounds.
• Theta oscillations help the brain segment continuous speech into smaller manageable units crucial for understanding the rhythmic and intonational structure of speech.
• EEG work shows that theta activity increases during tasks that involve syllable discrimination and repetition, suggesting the brain uses theta rhythms to organize and process syllabic information.

Neural Tracking

• Subtle phonemic differences such as cat vs. pat require distinguishing specific acoustic features, like voice onset time (VOT) or formant transitions.
• Gamma activity helps track rapid acoustic changes; gamma oscillations enhance temporal resolution, enabling precise temporal alignment between the neural response and subtle phonemic cues.
• "Tracking with higher fidelity" closely aligns the brain's neural oscillations (in multiple frequency bands) with the dynamic features of speech, such as syllable timing, pitch contour, and phoneme transitions.
• During tasks requiring fine acoustic discrimination, gamma activity is upregulated for high-resolution, short-timescale processing; lower-frequency bands (e.g., theta, delta) track slower modulations like syllable or word rhythms.
• The brain uses a hierarchical organization of frequency bands where different groups of neurons oscillate at different frequencies simultaneously.
• Delta Tracks sentence structure and intonation (0.5-4 Hz).
• Theta Tracks syllables (4-8 Hz).
• Gamma Tracks phonemes and fine acoustic features (30-100 Hz).
• Depending on the speech task, higher-level (delta/theta) or lower-level (gamma) oscillations may dominate.
• Brain adjusts balance across frequencies based on what's needed for the task.
• During phonemic processing, more gamma oscillations synchronize with the speech signal, focusing neural resources on fine auditory discrimination.

Why Kids Recover from Aphasia Better

• Children recover better from aphasia, because their brains are still developing.
• Brains are highly adaptable and not as specialized.
• Childhood plasticity allows other brain regions to step in and compensate for damaged areas.
• Adults have more rigid and specialized neural networks making recovery slower and less complete.
• The left hemisphere typically dominates language processing when damaged in adults, it causes severe long-lasting aphasia.
• The right hemisphere can take over language functions when the the dominant hemisphere is rendered defunct.
• Backup ability diminishes with age as the left hemisphere becomes more specialized and the right for other functions.

Bioprogram Hypothesis

• The systematic structure of creoles reflects a universal grammatical framework that is biologically hardwired, similar to what drives child language acquisition.
• Limited input leads to language through gap filling, universality, with a critical period.
• Children are exposed to full grammar, and the creole languages are not predictable, and not complex as input.

Infant Directed Speech

• Has a rhythmic cadence
• Repeats words frequently
• Hyperarticulated vowel space
• Higher pitch
• Exaggerated Intonation
• Slower tempo
• Simpler vocabulary
• Uses diminutives like doggy instead of dog

Differences in Speech

• Speech sounds = acoustic signals that languages use to express meaning.
• There are ~200 different speech sounds.
• English uses about 45.
• Duration, clicks, and tone make new speech sounds in some languages. Tonal languages use prosody to mark different words

What Sounds Signal Meaning

• Distinctive feature: An acoustic characteristic that makes a meaning difference is linguistically contrastive ([t] vs [d] in English).
• Phones: Different sounds that can be produced in a language.
• Allophones: Phones that don't differentiate meaning (p vs ph are allophones of the same phone in English).
• Phonemes: Meaningfully different sounds in a language (aspiration in some languages e.g. Hindi) or [s] vs. [∫] in English.

Allophones + Phonemes

• In English, p vs ph are allophones of the /p/ phone
• Switching allophones does not change word meaning. For example [sphlt] still means spit.
• Languages group phonemes differently; for example [p] & [ph] belong to the same phoneme in English, but different phonemes in Chinese. Switching [p] & [ph] changes the meaning of the word.
• Minimal pairs are pairs of words/phrases that differ in only one phonological element

Allophones and Phonemes Defined

• Phoneme = a sound's minimal unit that distinguishes between words.
• Allophone = different phonetic realizations of a phoneme in unique environments.

Phonological Contrasts Summary

• If sounds contrast in a language (e.g. [t] and [d] in English), the sounds form separate phonemes.
• Minimal pairs (e.g., [tuejn] vs. [duejn] "train vs. drain") distinguish the sounds.
• Example: [tuejn] vs. [duejn] (train vs. drain)
• If sounds do not contrast in a language.
• The sounds are allophones of a single phoneme.
• Sounds are in complementary distribution, which indicates the other never shows up.

Identifying a Minimal Pair

• Words must have the same number of sounds
• Words must have identical sounds except for one
• The different sound must be in the same position
• Words must have different meanings

Examples of allophone, phoneme, phones:

• /ra/ vs /la/:

  • Japanese uses these sounds as Allophones
  • English uses these sounds as Phonemes
  • Both are phones

• retroflex vs. dental /da/ sounds:

  • Hindi: Phonemes
  • English: Allophones (your doll vs. this doll)
  • Both: phones

Phonological Structure of Words

• Onset + Rime
  • Cat: onset= /c/ + rime= /aet/
• Implicitly know structure of words.
  • Rhyming is evidence!
  • Language Play in the form of Spoonerisms.
    • Dear old queen --> Queer old dean
    • Glad puppy --> Plad guppy
• We know 'kpakali'and 'zloty' are not words in English by way of Phonotactic Knowledge

Phonological Rules

• Pluralization happens through addition of the letter s to nouns
• English voicing assimilation Rule:
  • Voiced consonants get the /z/ sound with pluralization
  • Unvoiced consonants get the /s/ in pluralization
  • Kids know these rules by about age 4.
• Assimilation occurs when two consonants together in a word match in terms of voicing.

Describing Speech Sounds

• Phonetics: One symbol per sound
  • Using letters of the alphabet is not adequate for description as speech sounds should be bracketed as [ph]
• Phonemics: Just indicate the meaningfully different sounds

Describing Sounds Using Articulatory Phonetics

• Place of articulation: Where the vocal tract closes or constricts
• Manner of articulation: How the vocal tract closes or constricts
• Voiced vs. Voiceless: Do vocal cords help produce sound?

Articulation Points

• Bilabial: [p], [b], [m] using both lips
• Labiodental: [f], [v] using lip and teeth
• Dental: [0], [ð]
• Alveolar: [t], [d], [n], [s], [z], [1], [1]
• Postalveolar: [S], [3]
• Palatal: [j]
• Velar: [k], [g], [ŋ]
• Glottal: [h]

Manner of Articulation

• Stop: Consonant sounds are produced by fully stopping airflow.
• Nasal: Speech sounds made as the airstream goes through the nose as a result of lowering the soft palate (velum) at the mouth's back: /m/, /n/
• Fricative: consonant sound created by bringing mouth into position to block the passage of the airstream (but not making a complete closure) generating audible friction. * English /f/ or /v/
• Affricative: begins as a stop and releases as a fricative generally ('chair') "chair."
• Glide: sound phonetically similar to a vowel, but functions as a syllable's boudary.
• Liquid: tongue produces a resonant, vowel-like consonant /l/, /r/

Voicing

• Voicing is when vocal folds are closed and vibrate to produce sound
  • For an unvoiced sound vocal folds are pulled apart

Practice With Voicing

• Voiced phonemes /b/, /m/, /w/, /v/, /TH/, /d/, ///, /j/, /y/, /z/, /n/, /r/, /g/
• Unvoiced phonemes /p/, /wh/, /s/, /sh/, /ch/, /k/, /f/, /th/, /h/
• To Practice: Name the manner (not place) of articulation such as stop or plosive

Phonological Development

Prelinguistic Speech steps:

1. Reflexive: crying (vegetative sounds)
2. Cooing and laughing (happy sounds).
3. Vocal play: increase in consonant and vowel-like sounds, squeals growls.
4. Reduplicated/canonical babbling: dadadadada.
5. Non-Reduplicatedbabbling: range with vowel combos.

• Babies babble differently (before 10 months), subtle differences.
• Deaf infants babble in the same prelinguistic stages by way of using their hands instead of vocally,

Stages in vocal development

• Babbling Drift: babies babble depending on language

Word in Evolution Defined

• A word that does not resemble the referenced word is the protoword
• Yumyum/Guh Guh

During the First Year

• The structure of the vocal tract of Newborns is such that the tongue touches most of their mouth.
• During Vocal Play tongue has articulation with the following mechanisms: skeletal; muscles; sensory receptors in the throat; maturation.
• Babies babble later with many ear infections

Word Recognition

• Recognition is by matching to a sound with external word object
• Aspects include accent & gender

Learning Words

• Babies hear mispronunciations like Baby vs Vaby
• Do not understand word-gender connection until 10 months.
• 4.5 mo olds have visual fixation that shows bilingualism

Word Production

• Early: single + reduplication, for example mama or dada
• 18 mo begin to transform sounds

First words

• First words are simple and lack consistency
• Phonological idioms produce like words

Speech errors

Can include the following mispronunciations

Weak syllable deletion, final consonant deletion, Reduplication, Consonant harmony, Velar fronting.

Phonological Awareness Basics

• Understand rhyme, count syllables + know same onset

Phonological Development Theories

• Behaviorist theory states babies imitate/rewarded
• Universalist theories use a list to learn important sounds
• Biologically determined theory with anatomical factors
  • Commonality of the sound m.

Multisensory Theory

• Multisensory theory combines the importance of visual + audio-McGurk effect.

Explore language processing through split-brain studies and EEG bands. Split-brain experiments reveal brain lateralization. EEG bands (delta, theta, beta, gamma) play key roles in language.