CSD350 Exam 2

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Electrophysiology
record neurons using electrode (usually wire or glass) and the ACTION POTENTIALS, can measure cell voltage or currents
Is electrophysiology invasive?
YES, usually requires some sort of surgery
What is electrophysiology usually done on?
Animal models (limited circumstances in people)
What are glass electrodes for?
intracellular recordings (ex: "patch clump")
Whole cell intracellular recordings
electrodes filled with solution, stuck into brain tissue until contact with cell, researcher sucks up plasma membrane and records action potentials from single neuron
Electrodes for extracellular electrophysiology
records multiple neurons at once from outside of the cell with a metal electrode (metal, or four wires twisted together)
Utah Array
very small; measures many neurons in a local area at once; was used to control a robotic arm (Brain Gate 2)
Electrocortiography (ECoG)
grid of electrodes placed on surface of the brain to localize seizures in people with drug resistant epilepsy
Why is ECoG helpful if stroke is lateralized?
ECoG sees which electrodes where first involved and where it spread, if the stroke were all over this wouldn't help.
What is local field potential (LFP)?
the signal recorded from 100s of neurons near an electrode
Is ECoG invasive?
Highly
What is used with ECoG to see where electrodes are?
CT scan and MRI
How do you study human speech while using ECoG?
play different sounds while using electrodes then measure brain activity, phonemes, filter data & look at high frequencies
"brain-to-text"
many groups working on using ECoG, Utah arrays, or noninvasive EEG/fNIRs to decode thoughts in people who cannot speak
Types of Analysis
Peri-stimulus time histogram (PSTH) and Receptive field analysis
Peri-stimulus time histogram (PSTH)
make a plot that shows number of action potentials before/during/after stimulus, look at response timing + selectivity, line shows when it's on
Receptive field analysis
Play many different stimuli, see which cause the neuron to fire AP
High temporal
can test hypotheses about processes that happen quickly
High spatial
can know precisely where neural signals are coming from
Low temporal looks at things like
semantics
High temporal looks at things like
phonemes
What can fNIRS test?
conversations, turn taking in people each with fNIRS cap
What can fMRI test?
listening to sentences, find where this processing happens in the brain
What can EEG test?
testing whether responses to phonemes differ for non-native vs native English listeners
Holist view
language functions distributed across many brain areas
Localizationist view
specific language functions localized to a particular region
Where is Broca's area?
foot of inferior frontal gyrus, above lateral fissure, anterior to percental gyrus
Lesions in Broca's area cause what?
apraxia of speech (disfluent production)
Exner's center
2nd frontal gyrus just above Broca's, across from hand/motor cortex
Lesions in Exner's center cause what?
agraphia (impairment in writing)
Wernicke's area
center/posterior parts of superior temporal gyrus, extends to supramarginal gyrus
Lesions in Wernicke's area cause what?
impair comprehensions of spoken language
Supramarginal gyrus
adjacent to Wernicke's area
Lesions to supramarginal gyrus cause what?
impair syntax, semantics, and repetition
Angular gyrus
at the junction of temporal, parietal, and occipital lobes. at posterior part of the sulcus separating the superior temporal and middle temporal gyri
What is the angular gyrus important for?
reading, writing, and understanding sentences
The classic model
Broca's = language production ("non-fluent aphasia"), Wernicke's = language perception ("fluent aphasia"), Arcuate Fasiculus = connection between them
Critiques of classical model
Broca's is also involved in language comprehension, is wernicke's even real?
Modern view
We know where Broca's is, but not what it does. We know what Wernicke's does but not where
Evidence for localizationist view
lesions can sometimes lead to specific deficits (ex: loss of knowledge about tools or animals)
Evidence for holist view
Differences in aphasias can be explained by a single "general language factor"
Localizationist or Holist?
the truth is probably somewhere in between
Criticisms of Neuropsychology
Lesion extent different in every patient, Lesions damage white & gray matter, Lesions symptoms are not stable, Many symptoms are not all or one but degree, Important functions may be redundantly represented
What does fMRI measure?
BOLD (blood oxygen level dependent signal), ratio of oxygenated to deoxygenated hemoglobin - more oxygen needed for brain activity! measured with magnetic fields
fMRI is ___ spatial and ___ temporal
high, low
What does PET measure?
metabolism of certain molecules
PET is __ spatial and __ temporal
low, low
What does EEG measure?
electrical potentials at the scalp, this reflects groups of neurons firing
EEG is __ spatial and __ temporal
low, high
What does fNIRS measure?
BOLD (blood oxygen level dependent signal), ratio of oxygenated to deoxygenated hemoglobin - more oxygen needed for brain activity! measured because they absorb light differently
fNIRS is __ spatial and __ temporal
low, low
What does Electrophysiology measure?
electrical signals = action potentials (voltage of the cell membrane either inside or outside cell)
Electrophysiology is __ spatial and __ temporal
high, high
What does ECoG measure?
electrical signals, but these are from many groups of neurons firing, similar to EEG
ECoG is __ spatial and __ temporal
medium/high, high
What are sounds?
vibrations that travel through the air and propagate a pressure wave
Important parameters of sound waves
frequency & intensity/amplitude
Frequency
# of waves in one second (Hz) - pitch
Intensity/amplitude
magnitude of movements (dB) - loudness
Speech sounds are the outcome of a combination of gestures of several organs including multiple __ and __ acoustic cues
spectral, temporal
Acoustic Cues in Speech
• "Bands" in the spectrogram: Pitch/harmonics, prosody/melody
• Formants (vowel identity)
• Voicing (voice onset time /ba/ vs /pa/)
• Noise segments (sibilants and fricatives)
• Silence (stops & plosives)
• Duration and shape of formant transitions
Word comprehension relies on what?
lower spectral modulations (still need temporal content)
You get speaker identity from
spectral modulations (determines pitch)
What would the spectrogram of the sound that is heard from a limited number of electrodes in a cochlear implant look like?
smeared in frequency
Tonotopy
orderly representation of frequencies from low to high
The Dual Stream Mode
Bilateral, very cortically focused (like classic model)
Spectrotemporal analysis
the computation of which sound frequencies are modulated at which rates
Example of spectrotemporal analysis
patients with electrodes listen to speech stimuli, record ECoG signals, determine which spectral or temporal modulations each area is most sensitive to
How can we see pitch?
using scalp electrodes (EEG) in the neural signal itself
FFR is different for native vs. non-native speakers
true!
Spectral modulation
any change in frequency (how close the harmonics are - pitch)
Temporal modulation
any change in the spectrogram, independent of frequency
Vowels have more ___ modulation, stops have more ___ modulation
spectral, temporal
Why is speech perception hierachial?
Earlier stages of processing involve extracting & analyzing low level acoustic properties

Later stages involve combining low level features into more complex, language-specific phonological patterns
What are linguistic representations in the brain?
phonemes/phonetic features, semantics, prosody, syntax, etc.
Ex of how acoustic patterns must be converted to a "code" at multiple levels
appeared vs appealed
What generates speech?
coordinated control of many articulators
Phonemes can be classified according to their ___ and ___ of articulation
place, manner
What is the place of articulation and constriction location for the major articulator /d/?
coronal tongue & alveolar
What is the place of articulation for /b/?
labial
What is the constriction location of /th/?
dental
Constriction degree of /d/?
plosive
Constriction degree of /sh/?
fricative
Are the fundamental units of phonological representations segments (phonemes) or features?
FEATURES - they combine to form the speech sounds
The Feature Theory
languages do not vary without limit, but reflect a single general pattern which is rooted in the physical and cognitive capacities of the human brain
What is important about the superior temporal gyrus?
it responds to speech
Do electrodes respond to a group of phonemes or specific phoneme?
GROUP, specific category, manner features, consonants/vowels
Where is spectral model (acoustic features) best?
superior temporal plane (primary auditory cortex)
Where is articulation/phoneme model best?
around superior gyrus
Where is semantic model best?
superior temporal sulcus
Homo sapiens arouse 150-180 thousand years ago, but when did writing emerge?
5,400 years ago
What was early writing?
Egyptian hieroglyphs (pictorial)
What did simplified alphabets do?
Alphabets allow us to capture abstract concepts more efficiently
In alphabetic writing systems, letters represent ___
phonemes
In systems other than alphabets, symbols can encode
phonetic features, syllables, or whole words
What are some consistencies in writing systems?
direction of writing, letters usually 3 strokes or less with high contrast, shapes are common in natural scenes (common shapes L&T)
Reading involves small, jerky eye movements called what?
Saccades
The amount of detail we see is optimal at the center of eye fixation, called the what?
fovea
What does the Local Combination Detector (LCD) Model propose?
the brain has multiple levels of feature detectors

hierarchically organized, larger fragments of printed words are represented at each level
In right handed people, the __ premotor cortex is activated
left
In left handed people, the __ premotor cortex is activated
right
Reading printed letters activates the ___ ___ for writing the same letters!
motor region
From the LCD model, the more word-like a stimulus is, the more the anterior areas of the ventral occipitotemproal cortex will be ___
active
What is the order of cortex in the Local Combination Detector Model (simple to complex?)
thalamus (lateral geniculate nucleus), primary visual, secondary visual, higher order visual
How do you interpret Visual Word Form Area graphs?
barplot shows activity for each stimulus
Properties of the visual word form area (VWFA)
• VWFA responds to printed words regardless of location
• Detects identity of printed words (e.g. RAGE or rage)
• Detects identity of words regardless of font
• Has greater sensitivity to real than unreal printed words
• Responds more to printed than spoken words (but may
be activated during rhyme judgment!)
• For congenitally blind people reading Braille, VWFA more
active for real Braille than unreal Braille words!
For those who are illiterate VWFA may respond to ___ ___
visual objects
Greater reading skills means ___ more VWFA activity for words
more
When we write, what do we activate first?
phonological and semantic structures of words
What is a grapheme?
smallest unit of a writing system - can be letter, character, digit, punctuation mark
What is allographic conversion?
translating abstract letter identities into concrete forms (upper, lower? cursive?)
What does disruptions to left ventral occipitotemproal cortex often cause?
impair both reading and writing
When patients receive treatment to help reading or writing, it can ...
improve the other modality
Reading and writing probably rely on what?
a single orthographic lexicon
How does the central part of the brain relate to writing?
orthographic lexicon, graphemic buffer, phoneme-grapheme conversion
How does the peripheral part of the brain relate to writing?
allographic conversion (choosing letter to write) and graphomotor planning (writing) - motor cortex
Auditory Feature Analysis
spectral and temporal modulations in speech, process the acoustic waveform
Phoneme system
combine different acoustic features to determine if we heard /aa/ or /i/
Phonological lexicon
Way for the brain to store the auditory representation of a word (how it sounds)
Phoneme-grapheme conversion
Convert the sound into how it is written
Semantic system
what is the meaning of the word?

may be used over phonological lexicon if begins with thought
Orthographic lexicon
what is the spelling of the word (sequence of graphemes)
Graphemic buffer
limited capacity working memory system that maintains each grapheme in an activated state while writing (ex: remember how to write "a")
Graphomotor planning
actually writing down
What is the first stage of saying a word?
Lexical selection
What is lexical selection?
choosing the word; depends a lot on perspective of speaker/listener
What is second stage of saying a word?
Retrieval of the phonological code of target word
What is the third stage of saying a word?
Turn the set of phonemes into syllables
What is the fourth stage of saying a word?
Articulate the syllables
What controls speech production?
Coordination of articulators by lips, jaw, tongue, and larynx
What does the larynx do?
Controls pitch
Different articulators are controlled by ___ parts of the brain
different
Speech production is organized by ___ and ___ of articulation
manner, place
Sounds produced in a similar way are controlled by ___ brain areas
similar
Speaking involves what?
accessing the word, activating the brain areas controlling movement, and feedback
What helps us learn to speak?
hearing ourselves
What does the Directions Into Velocities of Articulators (DIVA) Model show?
How we incorporate interactions between thinking about what to say, controlling movements, and changing movements in response to what is heard/felt
Feedfoward Model
process of thinking about a sound/word to producing it - usually sufficient for well-learned movements
Feedback model
What happens after you produce the sound - important for learning pronunciations, vocal learning
The model is a ___ ____ that shows how different processes might help us learn to speak
computational framework
The model uses some of the ___ processes we think are going on in the brain
same
What is the first step of the model?
Specify auditory target and transmit to pathways (articulatory and auditory)
What is the articulatory component pathway
to control movements
What is the auditory component pathway?
to show what the sound should sound like if it's said correctly
What is the second step of the model?
It hears what is produced and the auditory output is COMPARED to auditory target
If there are auditory errors, what happens?
the motor system modifies the command
What is the third step of the model?
Acquires a somatosensory target representation (how target should feel to produce) & body position
What is the transition from learning to knowing?
At first, model relies on feedback, but then correct feedforward representation is learned and is resistant to lack of feedback
What happens when you perturb auditory feedback?
Delaying auditory feedback makes it difficult to produce speech
What happens when you perturb somatosensory feeback?
you compensate movements, so little change
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