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Lecture 7

NROC64H3 Lecture Notes - Lecture 7: Superior Olivary Complex, Ear Canal, Auditory Cortex


Department
Neuroscience
Course Code
NROC64H3
Professor
Matthias Niemeier
Lecture
7

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Lecture 7 - Multisensory Perception
Auditory System
- Responsible for the sense of hearing
- Divided into two subsystems:
o 1. peripheral auditory system:
outer ear, middle ear and inner ear
o 2. central auditory system: from
the cochlear nucleus up to the
primary auditory cortex
- Peripheral Auditory System:
o Outer Ear: consists of the pinna
that appear as folds of cartilage
Surround the ear canal and function as sound wave reflectors and attenuators
when the waves hit them
Helps the brain identify the direction from where the sounds originated
From the pinna, the sound waves enter a tube-like structure called auditory
canal sound amplifier; then sound will travel thru canal to the eardrum
o Middle Ear: Consists of eardrum and bones called ossicles
Three ossicles include the hammer (malleus), anvil (incus), and stirrup (stapes).
Convert sound vibrations when the sound waves hit the eardrum into sound
vibrations of higher pressure
o Inner Ear: filled with liquid rather than air, with the main structure called the cochlea
Where the sensory info in wave form is transformed into the neural form
The cochlear duct contains the Organ of Corti which is comprised of inner hair
cells that turn the vibrations into electric neural signals
Each hair innervates many auditory nerve fibers, and these fibers form the
auditory nerve
- The auditory nerve combines with the vestibular nerve forming cranial
nerve VIII or the vestibulocochlear nerve
- The cochlear nucleus is the first site of the neuronal processing of the
newly converted data from the inner ear
- It then goes to the trapezoid body is where some of these axons cross
over to the other side before traveling on to the superior olivary
nucleus
o This is believed to help with localization of sound
Sound waves enter the ear and travel thru external auditory canal before striking the ear
drum, and causing it to vibrate
Eardrum connects to malleus to the incus and to the stapes Stapes pushes in and out
to the OW, this action is passed on to the cochlea that consists of hair cells in the organ of
corti (inside the cochlea) these cells transmit vibration into electrical impulses to the
brain and nerves Organ of C has 4 rows of hair cells (1 inner row and 3 outer rows)
STAPES OW waves of sound thru cochlear fluid OOC into motion causing fibers
to resonate high frequency near OW and low F near end
Middle ear infection throat; common in children = everything a lot shorter in a child;
area in canal a lot shorter and easier for germs to get there because so small
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- Within the superior olivary complex lies the:
o 1- lateral superior olive is important in detecting interaural level differences
o 2- medial superior olive is important in distinguishing interaural time difference
- The lateral lemniscus carries information about sound from the cochlear nucleus to various
brainstem nuclei and ultimately the contralateral inferior colliculus of the midbrain
- The inferior colliculi acts to integrate information regarding sound source localization before
sending it to the thalamus and cortex
- Medial Geniculate Body is the relay station which acts as the gateway for auditory perception
- Primary auditory cortex: located on the superior temporal gyrus in the temporal lobe
o receives input from the medial geniculate
complex
o has a topographical map of the cochlea
o especially important for processing temporal
sequences of sound (i.e. speech) understand
words being said to you
- Perceptual timing has been studied using:
o duration discrimination and estimation if
play clip of sound, and estimate how long it was
o temporal bisection comparing temporal stimuli to durations held in memory; play 30
sec clip of a song, then played a 25 sec clip of the song, and asked if clip shorter or
longer than clip played earlier
o detection of anisochrony - timeshifts in music detecting off sequences
o beat alignment task detecting if a tune (metronome) over the song is going with the
beat or not
o sequences of durations requires extraction of the underlying beat and tapping to that
beat (when music stops)
o finger tapping asked to tap with finger along with song beat when played
- Test of Basic Auditory Capabilities (TBAC-E): 19 tests that focus on timing, pitch and loudness
perception, and auditory recognition
o selectively addressed auditory perception, and excluded production tasks
- Beat Alignment Test (BAT): set of tasks for assessing sensorimotor synchronization with a paced
tapping task and beat perception abilities
o It was found that larger tapping variability was associated with lower beat perception
- Harvard Beat Alignment Task (H-BAT): paced tapping to music (finger tapping),
perception/production of simple meters e.g.  ad  ad  ad  or  ad a  ad a three…,
sequences of tones with a tempo change (speed or pace of a given piece), and detecting/tapping
to the beat of patterns of time intervals (they change interval time every second or half for
example)
o better performance in a synchronization task is associated with lower perceptual and
motor thresholds
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- Battery for the Assessment of Auditory Sensorimotor and Timing Abilities (BAASTA): eight
tasks, four testing perceptual timing and five sensorimotor timing
- Perceptual tasks:
o 1. Duration discrimination: threshold for discriminating the duration of two tones was
estimated
o 2. Anisochrony detection with tones: threshold to detect a time shift in an isochronous
sequence of tones
o 3. Anisochrony detection with music: threshold to detect a time shift in a musical
excerpt
o 4. Beat Alignment Test: isochronous sequence was either aligned to the musical beat or
non-aligned
- Production tasks:
o 1. Unpaced tapping: assess the tapping rate and motor variability without a pacing
stimulus in regular, fast, and slow conditions
o 2. Paced tapping to an isochronous sequence: synchronize to a metronome
o 3. Paced tapping to music: synchronization to the beat of music
o 4. Synchronization-continuation: produce tapping at the same rate after tone stops
playing
o 5. Adaptive tapping: flexibility in adapting to a changing pacing stimulus
Webber fraction minimal threshold which you
can detect a change found that the duration
discrimination task was 10% higher than the
anisochrony task therefore it was harder because
more to detect but metronome and music
were easier (but they had their differences);
music was easier to detect than a metronome
Beat Alignment non-musicians (non-trained ears) could easily detect whether the metronome aligned
or not aligned with music on all the tempos easy to tell if metronome is on or off beat did’t atter
what kind of beat)
--------------------------------------------------------------------------------
Where ou’re ot listeig to usi of etrooe; just
tapping
Tapping rate is slowest in slow condition people were able
to slow down their tapping beat when requested; but more
comfortable to go faster than slower
- When they were asked to do spontaneous tapping = closer to faster speed than slow speed
CV = Coefficient of variation measure of variability; high = very variable in responses
- Motor variability did not change within groups same amount of variability in slow, fast and
spontaneous initially would have though faster would be higher variability but not TRUE
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