Neuropsychology: The Hearing Brain

Question 1

What is a sound?

Answer 1

-Composed when changes in air pressure occur
-Different types: pure tones (sinusoids) and more complex sounds

Question 2

What are characteristics of sounds?

Answer 2

Composed when changes in air pressure occur
-Caused by motion or vibration of object
-Changes in air pressure have physical properties
–>Amplitude: how low or high waves go, related to loudness
–>Frequency: how slow or fast waves go, related to pitch
-Humans only sensitive to specific sounds

Question 3

What are pure tones or sinusoids?

Answer 3

-Simplest sounds
-Sinusoid waveform
-Characteristic pitch
-Seldom heard in everyday life

Question 4

What are more complex sounds?

Answer 4

Sum of sinusoids

Question 5

What is the ear?

Answer 5

-3 main parts
-4-5 synapses in auditory pathway from ear to brain
-Spatial arrangement of auditory nerve and primary auditory cortex (PAC)

Question 6

What are the 3 main parts of the ear?

Answer 6

-Outer ear
-Middle ear
-Inner ear

Receptors activated upon sound arriving in ear

Question 7

What is the auditory pathway from ear to brain?

Answer 7

-Auditory nerve
-Cochlear nuclei in brainstem
-Medial geniculate nucleus (MGN) in thalamus
-Primary auditory cortex (A1, core)
-Core area surrounded by secondary auditory cortex (including belt and parabelt regions)

Information ascends and descends in pathway

Question 8

What are some characteristics of the primary auditory cortex (A1, core)?

Answer 8

-Main cortical area to receive auditory-based thalamic input
-Located in Heschl’s gyrus in temporal lobes

Question 9

What is the spatial arrangement of the auditory nerve and primary auditory cortex (PAC)?

Answer 9

Tonotopic organization: different neurons will hear different parts of auditory field

Question 10

What does a comparison between the auditory and visual system look like?

Answer 10

-Thalamo-cortical route
–>Auditory: MGN projects to A1
–>Visual: LGN projects to V1
-Organizing principle of early neural processing
–>Auditory: tonotopic organisation: orderly mapping between sound frequency and position on cortex
–>Visual: retinotopic organisation: orderly mapping between position of retina and position on cortex
-Temporal and spatial sensitivity
–>Auditory: temporal > spatial
–>Visual: spatial > temporal
-Functional specialization of feature processing
–>Auditory: less well documented
–>Well documented for color (V4) and movement (V5/MT)
-Higher-order context-dependent pathways
–>Auditory: evidence for separate auditory pathways for what vs where/how
–>Visual: evidence for separate visual pathways for what vs where/how

Question 11

What is the dorsal where/how stream of the auditory pathway?

Answer 11

-Neurons in auditory cortical areas specialized for coding where sound is from, regardless of context
-2 mechanisms to identify location of sound

Question 12

What 2 mechanisms are there to identify the location of sound in the dorsal where/how stream of sound?

Answer 12

-Mechanism 1: inter-aural differences
-Mechanism 2: distortions of sound by head and outer ear
(image)

Question 13

How does mechanism 1 work to identify the location of sound?

Answer 13

Inter-aural differences
-Differences between ears
-Time differences: sound arrives at one ear before other
-Intensity differences: sound less intense at farthest ear
-Picked up in Heschl’s gyrus (A1) and belt region (A2)

Question 14

How does mechanism 2 work to identify the location of sound?

Answer 14

Using distortions of sound wave by head and earlobes
-Sounds in left and right ear don’t sound exactly same
-Head-related transfer function: brain develops internal mode of how sounds get distorted by unique shape of ears and head, so able to infer likely location
-Picked up in planum temporale (posterior to A1)

Question 15

What is the ventral what stream of the auditory pathway

Answer 15

-Neurons in auditory cortical areas specialized for coding context of sound, regardless of where it’s from
-Auditory stream segregation: division of complex auditory signal
-Auditory memory implicated in auditory stream segregation
-2 brain regions strongly implicated: auditory cortex (mismatch negativity effect) and parietal cortex (role in spatial processing)

Question 16

What is the auditory stream segregation?

Answer 16

Division of complex auditory signal
-Separating input into streams
-Separating single stream into different objects and locations

Question 17

How is the auditory memory implicated in the auditory stream segregation?

Answer 17

-Involves input across time, not only input at one point in time
-Codes rather abstract properties of auditory stimuli

Question 18

What is the mismatch negativity (MMN) effect?

Answer 18

-Related to auditory cortex
-Occurs when sound is unexpected relative to preceding sounds
-Possible to segregate unexpected sound of other sounds
-Mismatch paradigm: standard sounds and deviant sounds: measured as EEG-signal of ERP-analysis
-Related to clinical conditions: meta-analysis of MMN-effects in schizophrenia

Question 19

How is the mismatch paradigm measured as differences in an EEG-signal of an ERP-analysis?

Answer 19

-Higher MMN-effect if difference between sounds larger
-MMN-effect not clear if difference not so prominent

Question 20

How is the MMN-effect related to schizophrenia (meta-analysis)?

Answer 20

-Longer duration of illness related to larger MMN-effect
-Effects stronger if mismatch in duration of tones, rather than frequency
-MMN marker for deficits in pre-attentive information processing
-MMN indexes ongoing neuropathological changes in auditory cortex of patients

Question 21

What is music perception?

Answer 21

-Music can be decomposed into different mechanisms
–>Melody vs rythm
–>Pitch vs temporal
-Specific problem with music: amusia
-Extremes: congenital amusia and absolute pitch

Question 22

What is amusia?

Answer 22

-Type of auditory agnosia
-Specific problem with music
-Music perception as whole (general) or as 1 of its mechanisms (specific) affected, more than perception of other sounds
-Only problems with high-level auditory processing: attaching meaning to music, recognition of music, etc.

Question 23

What is congenital amusia?

Answer 23

-Tone deafness
-Developmental difficulty in perceiving pitch relationships
-Increased grey matter in auditory cortex (right superior temporal gyrus) and frontal regions (right inferior frontal gyrus)
-Negative relation between how good somebody is in finding tones and cortical thickness

Question 24

What is absolute pitch?

Answer 24

-Ability to detect pitch of sound
-Smaller volume in right superior temporal cortex and planum temporale

Question 25

How is voice perceived?

Answer 25

-Voices convey socially important info (age, sex, gender, emotion)
-Voice selective region in superior temporal lobe (part of “what” stream), which responds to:
–>Vocal sounds, more than non-vocal sounds
–>Changes in identity of person, more than to other acoustic changes

Question 26

What are characteristics of speech perception?

Answer 26

-Speech is complex process
-Speech perception encounters different challenges
-Motor theory of speech perception
-Speech perception in brain
-Dual routes for speech perception: ventral what stream and dorsal how stream
-McGurk illusion

Question 27

Why is speech a complex process?

Answer 27

-Often damaged as seen in neuropsychology
-One of earliest functions to fall out in brain damage

Question 28

What different challenges does speech perception encounter?

Answer 28

-Gaps don’t occur between words that occur with certain consonants (that restricts flow of air)
-Problem of segmenting continuous input
-Problem of inter-speaker differences
-Co-articulation

Question 29

What is the segmentation problem?

Answer 29

-No overlap in visual auditory gaps in sentence
–>Visually: gaps between words
–>Auditory: gaps with certain consonants
-Especially in unfamiliar languages

Question 30

What is the problem of inter-speaker differences?

Answer 30

Pitch affected by age and sex; different dialects, talking speeds, etc.

Question 31

What is co-articulation?

Answer 31

Consecutive speech sounds blend into each other due to pronunciation

Question 32

What is the motor theory of speech perception?

Answer 32

-Hypothesis that people perceive spoken words by identifying gestures with which they are pronounced rather than identifying sound patterns that speech creates
-Revived after discovery of mirror neurons in premotor and inferior frontal regions: respond with motor movement and when seeing/hearing gestures in other people
-Evidence: (pre)motor regions play role in difficult speech signals

Question 33

How does speech perception in the brain work?

Answer 33

-A1 responds equally to speech and other sounds in both left and right hemispheres
-Areas more anterior to this in left hemisphere respond more to intelligible speech relative to unintelligible speech of similar acoustic complexity
-Left hemisphere particularly important for speech
–>Damage: pure word deafness

Question 34

What is pure word deafness?

Answer 34

-Type of auditory agnosia
-Damage to more anterior areas in left hemisphere
-Speech not identified: appears too fast or distorted
-Environmental sounds and music identified

Question 35

What is the ventral what stream of speech perception?

Answer 35

-Ventral route along temporal lobe
-Recognizes speech acoustically
-Discrete percepts mapped on abstract representations that specify nature of acoustic signal
-Important for speech comprehension and semantic knowledge
-Deep aphasia: deficit in how and what route

Question 36

What is the dorsal how stream of speech perception?

Answer 36

-Dorsal route along parietal and frontal lobes, connected through acruate fasciculus (white-matter tract)
-Recognizes speech motorically: related to motor theory of speech perception
–>Mirror neurons in premotor and inferior frontal cortices: respond with motor movement, but also when seeing/hearing gestures in other people
-Discrete percepts mapped onto units of articulation
-Important for saying and learning unfamiliar words
-(Pre)motor regions role with difficult speech signals
-Deficit: impaired repeating and learning of new phonology
-Deep dysphasia: deficit in how and what route

Question 37

What is deep dysphasia?

Answer 37

-Deficit in ventral what and dorsal how stream of speech perception
-Patients can’t repeat non-words and make semantic errors in repetition (hear “cat”, but say “dog”)

Question 38

What is the McGurk illusion?

Answer 38

-Posterior superior temporal sulcus important to link auditory and visual speech
-McGurk illusion example of how input from one sense influences perception of input other sense
–>Same sound heard differently based on how mouth moves
–>2 explanations: multisensory perception, or illusion arises from activating motor system for speech production
-Potential roles of regions (STS and inferior frontal) in categorical perception of ambiguous syllables

Question 39

What is the 1st explanation for the McGurk illusion?

Answer 39

Multisensory perception
-Info of both senses processed together
-Happens in left posterior superior temporal sulcus: TMS-evidence shows reduced illusion

Question 40

What is the 2nd explanation for the McGurk illusion?

Answer 40

Illusion activates other regions
-Activation in motor system for speech production, such as inferior frontal gyrus, due to connections between posterior superior temporal sulcus and dorsal regions

Question 41

What is categorical perception?

Answer 41

Continuous changes in input are mapped on to discrete percepts