Hearing & Language Processing

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Hearing Language Processing
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Structure of the Ear
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How the Ear Works

• The ear has three main parts the outer, middle
  and inner ear. The outer ear (the part you can
  see) opens into the ear canal. The eardrum
  separates the ear canal from the middle ear.
  Small bones in the middle ear help transfer sound
  to the inner ear. The inner ear contains the
  auditory (hearing) nerve, which leads to the
  brain.

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From Sound Wave to Nerve Impulse

• Any source of sound sends vibrations or sound
  waves into the air. These funnel through the ear
  opening, down the ear, canal, and strike your
  eardrum, causing it to vibrate. The vibrations
  are passed to the small bones of the middle ear,
  which transmit them to the hearing nerve in the
  inner ear. Here, the vibrations become nerve
  impulses and go directly to the brain, which
  interprets the impulses as sound (music, voice, a
  car horn, etc.).

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Otitis Media
Otitis media is an inflammation in the middle
ear (the area behind the eardrum) that is usually
associated with a buildup of fluid. The fluid may
or may not be infected. The Eustachian tube, a
passage between the middle ear and the back of
the throat, is smaller and more nearly horizontal
in children than in adults. Therefore, it can be
more easily blocked by conditions such as large
adenoids and infections. This allows bacteria and
viruses to find their way into the middle ear
more easily. Their tubes are also narrower and
less stiff, which makes them more prone to
blockage.
http//www.kidsource.com/ASHA/otitis.html
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Otitis Media How hearing becomes impaired

• Three tiny bones in the middle ear carry sound
  vibrations from the eardrum to the inner ear.
  When fluid is present in the middle ear, the
  vibrations are not transmitted efficiently and
  sound energy is lost. This is because the
  flexion of the membranes in the cochlea (which
  then causes the fluid to flow past the cilia and
  bend them for the sounds) is affected. The result
  may be a mild or even moderate hearing loss.
  Therefore, some speech sounds may be muffled or
  inaudible (note think about how this might
  affect phonemic processing during the first 3
  years of life during the critical period).
• Generally, this type of hearing loss is
  temporary. However, when otitis media occurs over
  and over again, damage to the eardrum, the bones
  of the ear, or even the hearing nerve can occur
  and cause permanent hearing loss.

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Primary Auditory Pathway

• Sound travels via the 8th cranial nerve
  (vestibulocochlear)
• Most of the fibers cross over to the
  contralateral side information received in the
  right ear is processed by the left hemisphere and
  vice versa

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From Nerve Impulse to Peception
Wernicke-Geshwind Model of Language

• 7 Components
• Primary Auditory Cortex
• Wernickes Area (22)
• Arcuate fasciculus
• Primary Visual Cortex
• Angular Gyrus
• Brocas Area
• Primary Motor Cortex

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Note in this model the dorsal and ventral
streams from the occipital lobe are not included,
only Area 39 that retrieves and assembles the
phonological code. This is the original model
that has since been elaborated.
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Original Wernicke-Geschwind Model of Language
from Rosenzweig, et al., 2002
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Subtractive Pet Scans Notice all the brain areas
affected
from Rosenzweig, et al., 2002
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What is aphasia?

• An impairment in language understanding or
  production that is caused by brain injury
• Brocas aphasia
• Wernickes aphasia
• Global aphasia
• Conduction aphasia
• Subcortical aphasia

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Brain Areas Affected in Aphasia
from Rosenzweig, et al., 2002
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from Rosenzweig, et al., 2002
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Dual Route Models for Reading Writing

• Reading

• Writing

Input (text)
Input (picture, spoken work)
Phonological Route
Whole-Word Route
Phonological Route
Whole-Word Route
Grapheme-Phoneme conversion
Orthographic Input lexicon
Grapheme-Phoneme conversion
Orthographic Input lexicon
Semantic System
Semantic System
Phonological Output
Written Output
Response
Response
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Dual Route Models for Reading Dyslexia

• Reading

• Phonological Dyslexia
• In this form of dyslexia, the problem occurs
  with attributing the correct sound (phoneme) to
  the grapheme (letter). Errors occur in sounding
  out unfamiliar words such as nonsense words
  because of the phoneme-grapheme impairment. Any
  familiar word, even an irregular familiar word,
  is readable (e.g. colonel).
• The phonological route is impaired.
• Errors also occur in the form of visual
  paralexias (e.g., leaf and lead).

Input (text)
Phonological Route
Whole-Word Route
Grapheme-Phoneme conversion
Orthographic Input lexicon
Semantic System
Phonological Output
Response
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Dual Route Models for Reading Dyslexia

• Reading

• Surface Dyslexia
• In this form of dyslexia, the problem occurs
  only with unfamiliar words (e.g., colonel), but
  sparing of regular (e.g., dog) or nonwords. The
  whole-word route is impaired, but the reader is
  able to apply the grapheme-phoneme conversion.
• Errors occur in understanding the meaning of
  words that sound the same (i.e. homophones such
  as son and sun).

Input (text)
Phonological Route
Whole-Word Route
Grapheme-Phoneme conversion
Orthographic Input lexicon
Semantic System
Phonological Output
Response
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Dual Route Models for Reading Dyslexia

• Deep Dyslexia
• This form of dyslexia is similar to phonological
  dyslexia, but the problem occurs only in reading
  nonwords or words that do not have strong visual
  or phonetic components (on, it,the).
• Substituting one word with another word that has
  a similar semantic meaning occurs Infant was
  crying is changed to Baby was crying (semantic
  paralexia).
• Etiology? Perhaps a disconnection between the
  phonological and the whole-word routes.

• Reading

Input (text)
Phonological Route
Whole-Word Route
Grapheme-Phoneme conversion
Orthographic Input lexicon
Semantic System
Phonological Output
Response
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A few final points

• Dysgraphia follows the same model as dylexia
  (phonolological, surface, deep)
• Impairment in prosody is a right hemisphere
  problem it can significantly affect the meaning
  of language.
• Typically, children do not fall into one distinct
  dyslexic subtype rather, they might have a
  stronger orientation or approach to reading that
  follows this model because of a problem that
  affects the other path (e.g., strong visual
  memory or visuospatial skills and otitis media
  affecting phonological processing).

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Visual and Spatial Abilities
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• Visual processing is accomplished in distinct
  neuroanatomic pathways.
• One such pathway, known as the where pathway
  involves a dorsal route through magnocellular
  thalamic cells to occipital and parietal cortices
  and conveys location and motion information.
• A second pathway, known as the what pathway
  involves a ventral route through parvocellular
  thalamic cells to occipital and temporal cortices
  and conveys color and form information.
• Note Subtle differences in this process as it
  applies to reading

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Neural Mechanisms for Reading the Left Hemisphere
Written word is sent along the ventral stream to
the word-form area (inferior temporal cortex),
which links the orthographic representation
(visual pattern) with the phonological code (Area
39). The neural networks that retrieve and
assemble phonological codes (Area 39) and those
that associate meaning with words are distributed
over the dorsal stream. Note This occurs in the
left hemisphere and reflects mature reading. In
young children, Wernickea area is more involved
as well as the ventral stream in the right
hemisphere (which later disengages) for
visuospatial information. Also, the left frontal
lobe becomes engaged and is associated with
reading fluency, which can be affected by frontal
lobe immaturity.
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philosophy.hku.hk/courses/cogsci/ncc.php
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What about the Right Hemisphere?

• Dorsal and ventral streams follow a similar
  pathway in the right hemisphere, but because
  there is complementary communication between
  hemispheres, some psychologists prefer to think
  of only dorsal and ventral streams as the basis
  for reading.
• Nonetheless, the brain is lateralized for
  speech/language in the left hemisphere and
  spatial processing in the right hemisphere.
• In the right hemisphere
• dorsal stream discrimination of spatial
  location (includes where the item is located in
  space).
• ventral stream discrimination of form
  (includes how to interact with an item) and is
  actively involved in early reading.
• Mathematics involves these spatial properties of
  the right hemisphere and later merges with left
  hemisphere language areas (i.e., math develops
  language components).
• Early reading involves the spatial components of
  the right hemisphere as well, until it becomes
  more lateralized to the left.