12: Audition

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12 Audition

• Chris Rorden
• Deb Hall, MRC Institute of Hearing Research
• Anatomy and function of the auditory system
• Brainstem disorders
• Word deafness
• Amusia
• Environmental sound agnosia
• Auditory neglect and extinction

www.mricro.com
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Anatomy and function source Ashmore, 2002

• The ear is a complex
• physiological apparatus,
• not just the visible
• outer ear
• - Reflection of sound in pinna provides spectral
  cues about elevation of a sound source
• - Middle ear is a cavity containing an ossicular
  lever which matches the acoustical impedance of
  the inner ear so sound energy is effectively
  transmitted (60)
• - Inner ear contains the cochlea where sound is
  converted into a neural signal
• - Sound energy is separated into frequencies
  (low energies at tip)

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Ear structures

• Peripheral
• Outer ear
• Middle ear
• Inner ear
• Auditory nerve
• Central
• Brainstem
• Midbrain
• Cerebral

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Outer Ear - Pinna
Pinna the projecting part of the ear lying
outside of the head (also called
auricle) Reflection of sound in pinna provides
spectral cues about elevation of a sound source
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Outer Ear Auditory Canal

• External auditory meatus
• Provides communication between middle and inner
  ears by conducting sound to the ear drum
• S-shaped tube _at_ 2.5cm long and _at_ 7mm wide
• Lining of the lateral 1/3rd of canal has cilia
  and glands
• Cerumen protects ear canal from drying out and
  prevents intrusion of insects

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Outer Ear - Ear drum

• Tympanic membrane
• Separates outer and middle ear
• Compliant
• Thin, three-layered sheet
• Epithelium of EAM outer layer
• Middle layer fibrous (strong) tissue
• Inner layer of middle ear mucous membrane

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Outer Ear - Ear drum

• Slightly concave to EAM, cone-shaped
• Most depressed and thinnest point is called the
  umbo cone of light (_at_ 2 mm)
• End of the attachment of malleus
• Slightly oval, taller than wide
• Otoscope if you pull the pinna up and back the
  tympanic membrane is visible

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Role of outer ear

• To augment the sound shadow
• Ear canal protects delicate parts of middle and
  inner ear from impact.
• To heighten our sensitivity to sounds
• Ear canal boosts sounds 15 to 16 dB between 1.5
  and 8 kHz (in the area of speech)
• This is due to resonance of ear canal
• Just like vocal tract this tube amplifies and
  dampens certain frequencies based on its length
  and composition

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Localization and shadowing

• Intensity differences louder if nearer, less
  shaded
• Inter-aural timing differences
• Frequencies influenced by location relative to
  pinna.

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Middle Ear Tympanic Membrane
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Middle Ear Eustachian Tube

• Establishes communication between middle ear and
  nasopharynx
• 35 to 38 mm long, typically closed
• Biological functions
• To permit middle ear pressure to equalize with
  external air pressure
• On the air plane, change in atmospheric pressure
  but not pressure in middle ear
• Yawning or swallowing opens pharyngeal orifice of
  tube to equalize pressures
• To permit drainage of normal and diseased middle
  ear secretions into the nasopharynx

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Middle Ear - Ossicles

• 3 of the smallest bones
• Malleus (hammer)
• Incus (anvil)
• Stapes (stirrup)
• Ossicular chain Transmits acoustic energy from
  tympanic membrane to inner ear
• Delivers sound vibrations to inner ear fluid
• Prevents the inner ear from being overwhelmed by
  excessively strong vibrations

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Middle Ear Ossicles
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Middle Ear Ossicles - Incus

• The ossicles give the eardrum mechanical
  advantage via lever action and a reduction in the
  area of force distribution
• Pressure Force/Area so less area more
  pressure
• the resulting vibrations would be much smaller if
  the sound waves were transmitted directly from
  the outer ear to the oval window.
• The movements of the ossicles is controlled
  muscles attached to them (the tensor tympani and
  the stapedius).These muscles can dampen the
  vibration of the ossicles, in order to protect
  the inner ear from excessively loud noise and
  that they give better frequency resolution at
  higher frequencies by reducing the transmission
  of low frequencies

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Cochlea and neighbors
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Tonotopic

• Base
• High Freq

• Apex
• Low Freq.

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Travelling wave

• Always starts at the base of the cochlea and
  moves toward the apex
• Its amplitude changes as it traverses the length
  of the cochlea
• The position along the basilar membrane atwhich
  its amplitude is highest depends on the frequency
  of the stimulus

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Traveling wave

• High frequencies have peak influence near base
  and stapes
• Low frequencies travel further, have peak near
  apex
• A short movie
• www.neurophys.wisc.edu/ychen/auditory/animation/a
  nimationmain.html

• Green line shows 'envelope' of travelling wave
  at this frequency most oscillation occurs 28mm
  from stapes.

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Anatomy and function source Hackney, 2002

• Many sound features are encoded before the signal
  reaches the cortex

• Cochlear nucleus segregates sound information
• Signals from each ear converge on the superior
  olivary complex - important for sound
  localization
• Inferior colliculus is sensitive to location,
  absolute intensity, rates of intensity change,
  frequency - important for pattern categorization
• Descending cortical influences modify the input
  from the medial geniculate nucleus - important as
  an adaptive filter

cortex
medial geniculate body
inferior colliculus
cochlear nucleus complex
cochlea
superior olivary complex
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Anatomy source Palmer Hall, 2002
Right hemisphere

• Primary non-primary auditory cortex

Sylvian Fissure
Medial Temporal Gyrus
planum polare (nonprimary AC)
Superior Temporal Gyrus
Superior Temporal Sulcus
planum temporale (nonprimary AC)
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Function source Palmer Hall, 2002
Intensity
Fast-rate temporal pattern in sound

• Numerous bilateral regions are
  frequency-dependent
• Overlapping regions are sensitive to intensity
  and to the temporal changes in sound
• One region is sensitive to the spatial
  properties of sound (RgtL)
• Speech also activates these regions, but neurons
  are probably responding to the complex acoustic
  properties in the sound.
• Perceptual attributes may be important

Right hemisphere
Slow-rate temporal pattern in sound
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• Sound intensity and activation
• Loud sounds (90 dB) activated posterior and
  medial temporal gyrus (red)
• Soft (70 dB) sounds activated area (yellow) is
  found most laterally of TTG
• Medium intensity (82 dB) sounds activated
  intermediate area (green). (NeuroImage 200217
  710)

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Auditory neuropsychology

• Simple modularity of function not clearly
  apparent
• - No auditory equivalents of V4 (visual colour
  area), V5 (visual motion area), fusiform face
  area etc
• - Cortical neurons respond to a complex array of
  stimulus features, and the temporal pattern of
  those features is important
• Unlike visual or somatomotor systems
• - A lot of auditory processing is supported by
  the ascending pathway
• - Studies in several mammalian species have
  demonstrated that bilateral ablations of the
  auditory cortex have little effect on simple
  sound intensity and frequency-based behaviours

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Brainstem disorders
Where is the lesion?
A
D
C
B
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Brainstem disorders source Griffiths et al. 1999

• Brainstem cochlear nucleus, superior olivary
  complex, inferior colliculus
• Lesions rarely compatible with life
• Multiple sclerosis can affect brainstem
• - Complete deafness is rare
• - MS patients do not report problems in everyday
  sound perception
• - Few systematic studies
• - Deficit in perceiving frequency changes
• - Deficit in detecting a gap in noise
• - Deficit in processing binaural cues for sound
  localisation

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Auditory agnosia

• A deficit in recognition

Perception
Recognition
Acoustical analysis
Representations
Auditory input
Apperceptive agnosia
Associative agnosia
Auditory agnosia is of this type
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Auditory agnosia source Griffiths et al. 1999

• Normal brainstem processing
• Midbrain impairment questionable
• Cortical deficit in perception
• - Preserved hearing (pure tones)
• - Disordered perception of certain sounds
• Speech - word deafness
• Music - amusia
• Environmental sounds - environmental sound
  agnosia

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A case of word deafness source Ellis Young,
1988

• Hemphill and Stengel (1940)
• I can hear you dead plain, but I cannot get
  what you say. The noises are not quite natural. I
  can hear but not understand
• - Normal pure tone audiometry
• - Fluent speech no errors of grammar beyond
  what is common for his particular dialect and
  standard of education
• - Normal reading
• - Normal writing and spelling
• - Poor spoken word repetition
• - Gross asymmetry between spoken and written
  word comprehension

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Word deafness source Ellis Young, 1988

• Associated symptoms
• - Some hearing loss (gt 20 dB HL)
• - Production (Brocas) aphasia
• - Perception of melody
• - Perception of environmental sounds
• Lesion site
• - Generally large bilateral infarcts
• - When unilateral, its more often the left
  hemisphere
• - Involves superior temporal lobe (non-primary
  auditory cortex)
• - May or may not involve Heschls gyrus (primary
  auditory cortex)

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Word deafness
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Frequency (kHz)
0
Time
- filtered harmonic sounds, broad band noise,
silent gaps - transitions in amplitude and
frequency on three time scales (milliseconds, 10s
of milliseconds, seconds) These temporal
transitions are rapid and complex
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Word deafness source Ellis Young, 1988

• Inability to make fine temporal discriminations
  and track rapidly-changing acoustic signals?
• There may be nothing speech specific about the
  impairment Ellis Young, 1988

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A case of amusia source Peretz, 1993

• Patient CN
• Symptoms
• - Unable to recognise even simplest tune
• - Unable to sing childrens songs that she had
  known well
• - No deficit in everyday verbal communication
• - No deficit in everyday recognition of
  environmental sounds
• Lesion site
• - Bilateral temporal lobe damage
• - When unilateral, its more often the right
  hemisphere

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Amusia source Peretz, 1993

• Dissociation within musical perception
• - Deficit in melody perception the variations
  in pitch
• - Deficit in rhythm perception the temporal
  organisation of melody over 100s of milliseconds
  or seconds time scale

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Amusia
Frequency
Time

• As in speech, music contains discrete harmonic
  sounds that vary over time
• melody local variation in features from note to
  note
• rhythm global variations in note duration that
  relate to a higher order pattern

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Environmental sound agnosia
source Griffiths et al. 1999

• Deficit rarely occurs in isolation

Environmental sounds contain fewer changes in
acoustic structure over time than an equivalent
length segment of speech or music
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A common deficit? No! source Peretz, 1993

• Word deafness, amusia and environmental sound
  agnosia are distinct
• - speech and music can dissociate after brain
  damage
• - music and environmental sounds can dissociate
  after brain damage
• - environmental sound perception can be
  selectively spared
• - recovery can follow different patterns (e.g.
  environmental sounds, then music then speech or
  in the reverse order)

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A common deficit? Yes! source Griffiths et al.
1999

• Word deafness, amusia and environmental sound
  agnosia probably co-occur
• - May not always be report because not all
  abilities are tested
• All 3 types of sound contain a mixture of
  acoustic features
• Deficit in an intermediate level of analysis,
  which is rarely tested
• - Analysing the spectro-temporal pattern in
  sound

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Auditory neglect source Pavani et al., 2003
Symptoms (a) Rightward biases in sound
localization (b) Poor relative judgements for
sounds on the contralesional side (c) Poor
elevation judgements for sounds on the
contralesional side Failure to detect
contralesional sound, when presented
concurrently Poor allocation of attention to
sounds separated in time
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Auditory neglect source Pavani et al., 2003
Lesion site - right inferior parietal lobe -
superior temporal gyrus - temporo-parietal
junction
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Auditory visual neglect A common deficit?
Yes! source Pavani et al. 2003

• Many neglect patients exhibit auditory, as well
  as visual, deficits.
• Correlation between severity of clinical visual
  neglect and experimental auditory neglect
  measures.
• Neglect can often be caused by damage to brain
  regions containing multisensory representations
  of space, with the deficit consequently
  manifesting across multiple sensory modalities,
  with correlated severity.

visual deficit
auditory deficit
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Visual extinction source Rorden et al., 1997
Symptom - a chronic bias of spatial attention
towards the ipsilesional side Hence,
ipsilesional events are perceived earlier than
physically synchronous contralesional stimuli.
This can be measured using the temporal order
judgements test.
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Visual extinction source Karnath et al., 2002
The same deficit is also found in audition
and over the same time scale ( 200
ms)
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Auditory visual extinction A common deficit?
Possibly! source Karnath et al. 2002

• Visual and auditory extinction have not been
  studied in the same patients
• ...but delay is of the same time scale
• It seems that the costs for information
  processing of contralesional events in
  extinction, induced by the bias of spatial
  attention towards the ipsilesional side, affect
  awareness of visual as well as auditory events to
  a similar degree.

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Science 2002 297 1706
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Key references

• (1) Signals and Perception 2002
• Ch1 The mechanisms of hearing by Ashmore
• Ch3 From cochlea to cortex by Hackney
• Ch4 Imaging central auditory function by Palmer
  Hall
• (2) Griffiths et al., Disorders of human complex
  sound processing Neurocase 5 365-378, 1999
• (3) Human Cognitive Neuropsychology by Ellis
  Young 1988
• Ch6 Recognising and understanding spoken words
• (4) Thinking in sound The cognitive psychology
  of human audition Editors McAdams Bigand 1993
• Ch7 Auditory agnosia A functional analysis by
  Peretz
• (5) Pavani et al., Auditory and multisensory
  aspects of visuospatial neglect. Trends in
  Cognitive Sciences 7407-414, 2003
• (6) Karnath et al., Impaired perception of
  temporal order in auditory extinction.
  Neuropsychologia 40 1977-1982 2002

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Additional references

• (7) Review of functional organisation of the
  auditory cortex
• Hall et al., Relationships between human
  auditory cortical structure and function.
  Audiology and Neuro-otology 8 1-18, 2003
• (8) Case studies of auditory agnosia
• References to many original papers can be found
  in (2) Griffiths et al., Disorders of human
  complex sound processing Neurocase 5 365-378,
  1999
• (9) A case of non-spatial auditory neglect
• Cusack et al., Neglect between but not within
  auditory objectsJournal of Cognitive
  Neuroscience 12 1056-1065 2000
• (10) Temporal order judgement deficits in visual
  neglect
• Rorden et al., Visual extinction and prior
  entry impaired perception of temporal order with
  intact motion perception after unilateral
  parietal damage. Neuropsychologia 35 421-433
  1997