Chapter 8: Hearing and Language Processing

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9 Apr 2012
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Chapter 8- Hearing and Language Processing
Module 8.1 The Auditory System
The Properties of Sound
o Frequency: rate of vibration, or number of wave cycles per unit time (Hz)
Human range: 20-20 000Hz max sensitivity 1000-4000
Dogs 20 000Hz +
Fish <2000
o Speed 340m/s
o Pitches: depend on frequency; higher frequency higher pitch
o Loudness: the amplitude of the sound wave
o Amplitude: sound pressure of the source
o Timbre: the complexity of the sound
o Fundamental frequency: intended frequency
o Overtones: at frequencies higher than but related to the fundamental frequency; vary in intensity
o Fourier analysis: break down complex sounds into simple components
o Sound is always moving and changing
o Prosody: tone of voice that can indicate cues
The Ear
o Capable of detecting and amplifying subtle vibrations and transforming them into neural signals
o Parts
Pinna: outermost visible portion of the ear
Auditory meatus: hole
External ear canal: amplifies vibrations and channels them on
Tympanic membrane/eardrum: vibrates and passes vibration along ossicles
Ossicles: malleus, incus and stapes; each successive bone amplifies the vibration and
transmits vibration
Oval window: has a membrane over it that transmits vibrations into the cochlea through the
cochlear fluid
Cochlea: shell; has inner (receptors) and outer (modulate) hair cells; more outer than inner
but inner serve as receptors
Cochlear fluid: vibrations of the fluid cause a bending of both basilar membrane and
tectorial membrane
Basilar membrane and tectorial membrane: bending of it elicits neural activity in hair cells
Hair cells: are receptor cells of the auditory system
Organ of Corti: hair cells, their cilia and cells that support them
Outer ear: pinna and external ear canal that catches and amplifies sound waves
Middle ear: chamber and contents between tympanic membrane and oval window; signal is
transduced to variations in air pressure to mechanical energy
Inner ear: mechanical energy is turned into neural activity
o tonotopic
Frequency specific sensory organization; as you go down toward apex more sensitive to
lower and lower frequencies
o Functioning may be influence by cognition ex. Experience can alter outer hair cells
o Efferent projections from cochlea show differential activation in different conditions
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Auditory Pathways
o Several functionally distinct and complex pathways that may be interconnected
o One pathway
Eighth cranial nerve vestibulocochlear nerve carries info from cochlear nerve to ipsilateral
cochlear nuclei
Ipsiliateral cochlear nuclei project to ipsilateral or contralateral superior olives and some
directly to inferior colliculus
Olivary nucleus ipsilateral to inferior colliculus
Some then travel contralateral side and others to medial geniculate nucleus of thalamus
then to primary auditory cortex
There is some crossover at both cochlear nuclei and inferior colliculus but most is ipsilateral
o Another
All have same destination until inferior colliculus where they then synapse on dorsal medial
genicular nucleus if thalamus and then directly to secondary and tertiary auditary cortices
Auditory Cortex
o Primary auditory cortex: in lateral fissure; highly specialized to respond to certain frequencies of
sound; is organized in a tonotopic fasion
Arranged in columns with anterior responding to higher frequencies and posterior lower
frequencies
Cortical regions respond to a smaller range of frequencies than neurons earlier in processing
stream
o Secondary auditory cortex: located lateral and anterior to primary auditory cortex
Little is known but neurons appear to be highly selective to the stimuli they respond to
Module 8.2 Language Systems in the Brain
Models of Spoken Language
o Gall Spurzheim and Broca: language was in frontal lobe
o Wernicke: complicated model; one area responsible for output of spoken language (broca) and
another for mapping sounds to words (wernickes area); and both are connected (by arcuate
fasciculus)
o Lichtheim: Wernickes area maps sounds to words but concept center ascribes meaning to those
sounds
o Wenick-Lichtheim-Geschwind (WLG) model: included a angular gyrus that receives projections
from visual areas and is the basis for visual language
Spontaneous speech: produced by accessing the mappings of sounds to meanings in
Wernicke's area, projecting this info to Brocas where motor program is formulated and
executed by motor cortex
Support
Accounts for visual language processing. Accounts many clinical speech disorders and
has been confirmed by electrical stimulation and functional neuroimaging studies
Problems
Oversimplification and omission
Models of Visual Language
o Auditory language abilities develop earlier and are more implicit than visual language abilities
o Classes of visual language models: single route models and dual route models
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