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Chapter 9: Hearing and Language
Chapter Summary, Outline, and Key Terms
Brief Chapter Summary:
Chapter 9 explains the physiological mechanisms involved in audition and language, two
processes that are inherently linked. The chapter begins with the auditory system and a
description of the outer and inner ear and the auditory cortex. Frequency analysis is then
introduced with a discussion of frequency theory, place theory, and analysis of complex
stimuli. The section dedicated to audition concludes with a discussion of sound
localization, emphasizing binaural cues and the brain circuits specialized for processing
them. The second half of the chapter deals with language. First, the brain regions
responsible for (a) language production and (b) language comprehension are described.
Structures that account for reading and writing are then detailed, along with a description
of the Wernicke-Geschwind model. The process of recovery from aphasia is addressed.
The chapter ends with a discussion of the controversy over whether the language
structures are a dedicated language generating mechanism, and a consideration of
language capability in non-humans, such as chimpanzees.
Outline and Key Terms:
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A receptor is a cell, often a neuron, that responds to a particular form of energy
(e.g., sound)
An adequate stimulus is the energy form for which the receptor in question is
specialized
Sensation is the acquisition of sensory information
Perception is the processing of sensory information
I. Hearing
A. The Stimulus For Hearing
1) Vibration in a conducting medium is the adequate stimulus for audition
2) Physical and psychological characteristics of sound
(a) Frequency refers to the number of waves or cycles of sound per second
(b) Pitch is the experience of sound frequency
(c) Amplitude (intensity) is the physical energy in a sound
(d) Loudness is the experience of sound energy (intensity)
(e) Pure tones are composed of a single frequency
(f) Complex sounds are made up of multiple frequencies
B. The Auditory Mechanism
1) The Outer and Middle Ear
(a) The outer ear (pinna) captures sound then amplifies it by funneling it into the
smaller auditory canal
(b) The tympanic membrane is particularly sensitive; it transmits vibrations to the
ossicles and inner ear
(c) The ossicles transfer vibration from the tympanic membrane to the cochlea
2) The Inner Ear
(a) Sound is analyzed within the cochlea
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i. The vestibular canal is the entry point for vibration
ii. The vibration travels through an opening into the tympanic canal
iii. The cochlear canal contains the auditory receptors
iv. The organ of Corti is the sound analyzing structure
v. The basilar membrane supports the organ of Corti
vi. The tectorial membrane overlies the hair cells and the basilar membrane
(b) Hair cells
i. When the hair cells vibrate, potassium channels open and the cell membrane
depolarizes. This initiates impulses in the neuron attached to the hair cell
ii. Inner hair cells are required for hearing
iii. The role of the outer hair cells is uncertain
3) The Auditory Cortex
(a) Neurons from the cochleas form part of the auditory nerves, pass through brain
stem nuclei to the inferior colliculi, to the medial geniculate nucleus of the
thalamus, and then to the auditory cortex
(b) There are more projections from each ear to the contralateral (opposite) side of
the head than to the ipsilateral (same) side
(c) The auditory cortex is topographically organized
(d) Secondary processing areas process and interpret complex sounds
(e) The dorsal stream projects from the auditory cortex through the parietal area to
the frontal lobes. It determines the location of a sound source and orients eye and
body movements toward it.
(f) The ventral stream distinguishes among sounds
C. Frequency Analysis
1) Frequency Theories
(a) Frequency theory (also known as telephone theory) states that individual
neurons in the auditory nerve fire at the same frequency as the rate of vibration of
the sound source.
(b) Volley theory states that groups of neurons follow the frequency of a sound
where individual neurons cannot, by “taking turns” firing
2) Place Theory states that the frequency of a sound is identified by the location of
maximal vibration on the basilar membrane and which neurons are firing most often
(a) Békésy found that the basilar membrane’s frequency selectivity is due to
difference in elasticity
(b) Because the auditory cortex is topographically organized, it contains a tonotopic
map, meaning that each successive area responds to successively higher
frequencies
(c) The brain uses place analysis: it compares the rate of firing in neurons of adjacent
places on the basilar membrane
(d) Frequency-place theory: low-frequency sounds are analyzed according to the
frequency theory and high-frequency sounds according to place analysis
3) Analyzing Complex Sounds
(a) Fourier analysis is the breakdown of a complex waveform into its sine wave
components
(b) The basilar membrane performs a Fourier analysis of a sound
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(c) The cocktail party effect is the ability to distinguish meaningful sounds among a
complex background of sounds
(d) Efferent activity apparently emphasizes some sounds by lengthening and
shortening outer hair cells
(e) Auditory objects are discrete sounds we recognize
D. Locating Sounds with Binaural Cues
1) Binaural Cues
(a) Difference in intensity – the near ear receives the most intense sound
(b) Difference in time of arrival – humans can detect difference in time of arrival as
small as 10 microseconds
(c) Difference in phase – some auditory neurons respond only to phase differences
2) Brain Circuits for Locating Sounds
(a) The neural circuit for detecting differences in time of arrival is most well
characterized
(b) This circuit is located in the superior olivary nucleus
(c) Coincidence detectors fire most when receiving input from both ears at once
II. Language
A. The Brain Structures of Language
1) Broca’s Area is responsible for the production of language.
(a) Broca’s aphasia is language impairment characterized by:
i. Non-fluent speech
ii. Anomia (Trouble finding the right words)
iii. Difficulty with articulation
iv. Agrammatic speech
(b) Vocalization is not lost in patients with damage to Broca’s area, but the ability to
translate information into meaningful speech is compromised
2) Wernicke’s Area is responsible for language comprehension, both in production and
reception.
(a) Wernicke’s aphasia is language impairment characterized by:
i. Speech fluent and articulate but meaningless
ii. Patient is unaware that anything is wrong
(b) Patients respond to conversation even though their own speech is meaningless
3) The Wernicke-Geschwind Model
(a) Hypothesizes that language is produced through an interaction of Wernicke’s and
Broca’s area
i. Writing a response to an orally presented question involves progression from
the auditory cortex to Wernicke’s area, to the angular gyrus where a visual
pattern is elicited
ii. In reading aloud, visual information is translated into auditory form by the
angular gyrus, sent to Wernicke’s area and finally to Broca’s area
(b) This model is simple but problematic; language likely requires all four lobes and
dozens of other brain areas
4) Reading, Writing and Their Impairment
(a) Alexia is the inability to read
(b) Agraphia is the inability to write
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(c) The angular gyrus connects the visual projection area with the auditory and
visual association areas in the temporal and parietal lobes
(d) Dyslexia (a reading impairment) can be acquired through damage, although it is
more commonly developmental.
(e) The planum temporale is usually larger in the left hemisphere, but in dyslexics,
this area is often the same size in both hemispheres
(f) Visual-perceptual difficulties are common in dyslexia
(g) The magnocellular theory of dyslexia, hypothesizes that the deficiency extends to
other magnocellular systems and accounts for auditory as well as visual
impairments
(h) The phonological theory, hypothesizes that the fundamental problem is not in
visual or auditory processing, but involves an impairment of phoneme processing
Recovery from Aphasia
1) Can occur within the first two years
2) Recovery is a testament to brain plasticity
The Role of the Right Hemisphere
1) Prosody is the use of intonation, emphasis and rhythm in speech
2) The right hemisphere is important for understanding meaning conveyed in speech
A Language Generating Mechanism?
Because humans seem to be innately programmed for language acquisition, some
researchers hypothesize that a language acquisition device within the brain is devoted to
language
1) Innate Brain Specializations
(a) Although there is not a single center, over 90% of right-handed individuals and 67
to 75% of left-handed individuals have their primary speech control in the left
hemisphere
(b) In the majority of cases, Broca’s area is larger and the lateral fissure and planum
temporale are longer in the left than in the right hemisphere
2) Location of Other Languages
(a) Sign language activates the same left-hemisphere areas as spoken language, and
left hemisphere damage causes significant, enduring impairments in sign language
(b) The right hemisphere’s involvement in sign language is probably due to the
language’s spatial characteristics
(c) Different regions of the brain are used to learn a second language in adulthood;
this separation is so distinct that injury can cause the loss of one language but not
the other
Language in Nonhumans
1) Animal Language Research
(a) Adult chimpanzees have been taught to sign, but critics argue that they can’t form
meaningful sentences
(b) A few younger animals have learned sign language with greater proficiency, but
no better than a two year old human child
2) Neural and Genetic Antecedents
(a) Many social animals respond better when meaningful auditory stimuli are
presented to their left hemisphere
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(b) Animal research suggests that we share similar brain structures with other
animals, which may have provided the foundation for our own language
development
(c) Humans and monkeys have mirror neurons in Broca’s area, which respond when
we mimic tasks and observe similar tasks in others
(d) The FOXP2 gene may play a role in the evolution of language
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