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Audition
• Chris Rorden
• Deb Hall, MRC Institute of Hearing Research
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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 (earlobe) 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
Ear structures
 Peripheral
–
–
–
–
Outer ear
Middle ear
Inner ear
Auditory nerve
 Central
– Brainstem
– Midbrain
– Cerebral
Localization and shadowing
–
–
–
High frequencies: intensity differences: louder if
sound is not in head’s sound shadow
Low frequencies: Inter-aural timing differences
Elevation: Frequencies influenced by location
relative to pinna.
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
– Changes impedance: large, weak
movement of ear drum turned to small,
forceful movement in cochlear liquid.
– Muscles can dampen response: Prevents
the inner ear from being overwhelmed by
excessively strong vibrations
Cochlea and neighbors
Tonotopic
Base
 High Freq
–
Apex
–
Low Freq.
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
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/animationmain.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
 Primary & non-primary
auditory cortex
Right
hemisphere
Sylvian
Fissure
Medial
Temporal
Gyrus
planum polare
(nonprimary AC)
Superior
Temporal Gyrus
Superior Temporal Sulcus
Heschl’s gyrus
(primary AC)
planum temporale
(nonprimary AC)
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Function source : Palmer & Hall, 2002
• 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 (R>L)
• Speech also activates these regions,
but neurons are probably responding
to the complex acoustic properties in
the sound.
•Perceptual
attributes
may
be
important
L
L
H
H
H
L
L
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 2002;17: 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 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
Auditory
input
Recognition
Acoustical analysis
Representations
“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 (> 20 dB HL)
- Production (Broca’s) aphasia
- Perception of melody
- Perception of environmental sounds
Lesion site
- Generally large bilateral infarcts
- When unilateral, it’s more often the left hemisphere
- Involves superior temporal lobe (non-primary auditory cortex)
- May or may not involve Heschl’s gyrus (primary auditory cortex)
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Frequency (kHz)
Word deafness
8
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 children’s 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, it’s more often the right hemisphere
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Amusia source : Peretz, 1993
 Dissociation within
musical perception
- Right injury - Deficit in melody
perception: the variations in pitch
- Left injury - Deficit in rhythm
perception:
the
temporal
organisation of melody over 100s
of milliseconds or seconds time
scale
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Frequency
Amusia
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 – usually right hemisphere
- inferior parietal lobe
- superior temporal gyrus
- temporo-parietal junction
Auditory & visual neglect : A common
deficit? Yes! source : Pavani et al. 2003
Many neglect patients exhibit auditory, as
well as visual, deficits.
visual deficit
Correlation between severity of clinical
visual neglect and experimental auditory
neglect measures.
auditory deficit
“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”.
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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)
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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Seifritz et al. 2002
Heschl’s Gyrus shows
sustained response to
sounds, surrounding
regions respond to onset.
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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 7:407-414, 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: 365378, 1999
(9) A case of non-spatial auditory neglect
Cusack et al., Neglect between but not within auditory objects
Journal 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