Neuropsychology: The Hearing Brain Flashcards
What is a sound?
-Composed when changes in air pressure occur
-Different types: pure tones (sinusoids) and more complex sounds
What are characteristics of sounds?
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
What are pure tones or sinusoids?
-Simplest sounds
-Sinusoid waveform
-Characteristic pitch
-Seldom heard in everyday life
What are more complex sounds?
Sum of sinusoids
What is the ear?
-3 main parts
-4-5 synapses in auditory pathway from ear to brain
-Spatial arrangement of auditory nerve and primary auditory cortex (PAC)
What are the 3 main parts of the ear?
-Outer ear
-Middle ear
-Inner ear
Receptors activated upon sound arriving in ear
What is the auditory pathway from ear to brain?
-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
What are some characteristics of the primary auditory cortex (A1, core)?
-Main cortical area to receive auditory-based thalamic input
-Located in Heschl’s gyrus in temporal lobes
What is the spatial arrangement of the auditory nerve and primary auditory cortex (PAC)?
Tonotopic organization: different neurons will hear different parts of auditory field
What does a comparison between the auditory and visual system look like?
-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
What is the dorsal where/how stream of the auditory pathway?
-Neurons in auditory cortical areas specialized for coding where sound is from, regardless of context
-2 mechanisms to identify location of sound
What 2 mechanisms are there to identify the location of sound in the dorsal where/how stream of sound?
-Mechanism 1: inter-aural differences
-Mechanism 2: distortions of sound by head and outer ear
(image)
How does mechanism 1 work to identify the location of sound?
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)
How does mechanism 2 work to identify the location of sound?
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)
What is the ventral what stream of the auditory pathway
-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)
What is the auditory stream segregation?
Division of complex auditory signal
-Separating input into streams
-Separating single stream into different objects and locations
How is the auditory memory implicated in the auditory stream segregation?
-Involves input across time, not only input at one point in time
-Codes rather abstract properties of auditory stimuli
What is the mismatch negativity (MMN) effect?
-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
How is the mismatch paradigm measured as differences in an EEG-signal of an ERP-analysis?
-Higher MMN-effect if difference between sounds larger
-MMN-effect not clear if difference not so prominent
How is the MMN-effect related to schizophrenia (meta-analysis)?
-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
What is music perception?
-Music can be decomposed into different mechanisms
–>Melody vs rythm
–>Pitch vs temporal
-Specific problem with music: amusia
-Extremes: congenital amusia and absolute pitch
What is amusia?
-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.
What is congenital amusia?
-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
What is absolute pitch?
-Ability to detect pitch of sound
-Smaller volume in right superior temporal cortex and planum temporale
How is voice perceived?
-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
What are characteristics of speech perception?
-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
Why is speech a complex process?
-Often damaged as seen in neuropsychology
-One of earliest functions to fall out in brain damage
What different challenges does speech perception encounter?
-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
What is the segmentation problem?
-No overlap in visual auditory gaps in sentence
–>Visually: gaps between words
–>Auditory: gaps with certain consonants
-Especially in unfamiliar languages
What is the problem of inter-speaker differences?
Pitch affected by age and sex; different dialects, talking speeds, etc.
What is co-articulation?
Consecutive speech sounds blend into each other due to pronunciation
What is the motor theory of speech perception?
-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
How does speech perception in the brain work?
-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
What is pure word deafness?
-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
What is the ventral what stream of speech perception?
-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
What is the dorsal how stream of speech perception?
-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
What is deep dysphasia?
-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”)
What is the McGurk illusion?
-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
What is the 1st explanation for the McGurk illusion?
Multisensory perception
-Info of both senses processed together
-Happens in left posterior superior temporal sulcus: TMS-evidence shows reduced illusion
What is the 2nd explanation for the McGurk illusion?
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
What is categorical perception?
Continuous changes in input are mapped on to discrete percepts
