Auditory system

Question 1

What happens when energy moves through a medium?

Answer 1

The molecules in that medium collide.

The denser the molecules are packed, the greater the probability of collisions (solids>liquids>gases)

Question 2

What is a pressure wave?

Answer 2

the chain of molecular collisions resulting from the introduction of mechanical energy to a medium

Question 3

The two components of a pressure wave

Answer 3

compression and rarefaction

Question 4

compression

Answer 4

the temporary density increase at the start of a wave as a result of molecules colliding

Question 5

rarefaction

Answer 5

temporary decrese in density in the wake of the pressure wave

Question 6

4 components of a sound wave

Answer 6

wavelength
amplitude
complexity
phase

Question 7

What is frequency?

Answer 7

Refers to how often each compression rarefaction cycle occurs per unit of time

measured in Hz
corresponds to the psychological dimension of pitch (pitch increase with frequency)

Humans perceive tones between 20-20k Hz, and as we ag,e high frequencies are the first to go

Question 8

Amplitude

Answer 8

refers to the peak height of the sound wave (how much compression occurs)

Corresponds to the psychological dimension of loudness (loudness increases with amplitude)
Typically measured in Decibels

Multiplying the pressure of a sound by 10 adds 20 decibels
, ex. 20Db= 200 sound pressure

Question 9

Phase

Answer 9

refers to where a wave is at in its compression rarefaction cycle at a given moment in time,

The degree of phase is measured by its phase angle

Question 10

Are sound waves additive?

Answer 10

yes, if 2 sound waves are in phase, there amplitudes will add and the sound will be twice as loud (like a dap)

If 2 waves are out of phase, the sounds will cancel each other and you will not percieve anything
Like noise cancelling head phones)

Question 11

complexity

Answer 11

refers to the source-specific variation in waveform

Pure sine waves are rare in nature

even different musical instruments generating the same note will have very different waveforms

the psychological correlate is timbre

Question 12

Harmonic complexity

Answer 12

Natural sound sources consist of vibration at multiple frequencies (harmonics) an the combo of all these frequencies is the sounds harmonic structure.

Question 13

Fourier’s Theorem

Answer 13

Any periodic sound can be decomposed into the sum of its harmonics (sine waves)

Any periodic sound can be synthesized by adding together the appropriate harmonic components

Question 14

What 3 parts is the ear composed of?

Answer 14

Outer, Middle, and Inner

Question 15

2 main parts of the outer ear

Answer 15

The pinna and the Auditory canal

Question 16

The pinna

Answer 16

external ear

Question 17

Auditory canal

Answer 17

Protects the delicate middle ear

dimensions - 1.3’ long and .25’ wide
acts as a resonant frequency amplifier

Question 18

Resonant frequency amplification

Answer 18

Resonance: an interaction between sound waves entering a medium and exiting that medium

resonant frequency- the frequency for which these entering and exiting waves add together, amplifying that frequency of the sound wave
(blowing in soda bottle)

Question 19

Resonance chamber

Answer 19

The range of frequencies that get amplified depends on the size and shape of the resonance chamber

The RF decreases as you increase the chamber’s length

Question 20

What 2 main parts in the Middle ear composed of

Answer 20

The eardrum and the ossicles

Question 21

The eardrum

Answer 21

a thin layer of skin that vibrates in response to a pressure wave entering the auditory canal

Question 22

Ossicles

Answer 22

Three tiny interconnected bones
malleus (hammer)
incus (anvil)
stapes (stirrup)

Question 23

Middle ear amplification- the air to water impedance problem

Answer 23

The fluid-filled middle ear requires 1000x more energy to vibrate than air

to compensate- the energy is focused on a smaller area, amplifying the signal.
The ossicles are used as a lever to apply greater force on the oval window (inner ear)

This amplification offsets 80% of the signal loss that would otherwise occure

Question 24

The inner ear

Answer 24

Cochlea- the structure containing the sensory transducers for audition

consists of 3 canals
the vestibular, the tympanic, the cochlear duct

Question 25

The vestibular and tympanic are

Answer 25

filled with a liquid called perilymph, but are separated until the very apex of the cochlea called the heliocotrema where they come together.

Question 26

Auditory process of the inner ear

Answer 26

The stapes moves against the oval window, creating a pressure wave that travels down the vestibular canal to the helicotrema, then back along the tympanic canal to the round window, this is where the pressure wave ends

Question 26

The Cochlear duct

Answer 26

Isolated from the vestibular canal by reissner's membrane and from the tympanic canal by the basilar membrane filled with endolymph (rich in K ions)

Question 27

The organ of corti

Answer 27

Consists mainly of the tectoral membrane and hair cells

Question 28

2 types of hair cells

Answer 28

Outer hair cells Relatively abundant; about 12,000/ear Embedded in the tectorial membrane Inner hair cells Relatively few (about 3,500/ear) Not embedded in tectorial membrane; just protruding into the gap

Question 29

The Auditory transduction event

Answer 29

The basilar membrane starts to vibrate in response to a pressure wave. This vibration moves the organ of Corti, causing a shearing force on the hair cells When the hair cells move, the receptor channels open, allowing K ions to flow in, the cell polarizes and fires

Question 30

The auditory pathways

Answer 30

The auditory nerve first goes to the ventral cochlear nucleus in the brain stem Superior olive sends info from both ears is combined and sends feedback to the contralateral (opposite) cochlea Inferior colliculus in the midbrain coordinates eye movements to sound sources

Question 30

Spiral ganglion cells

Answer 30

Located in the organ of corti, their dendrites synapse on the hair cells, their axons leave the inner ear as the auditory nerve

Question 30

2 types of spiral ganglion cells

Answer 30

Type 1 Fibers most abundant (95%) synapse on the inner hair cells very redundant; about 15 fibers per each inner hair cell carries the primary auditory signal Type 2 Fibers synapse on the outer hair cells each fiber synapses on about 10 outer hair cells thought to tune the Type 1 responses

Question 31

The medial geniculate nucleus Center-surround coding of sound frequency

Answer 31

Preferred Frequency (The "Center") Each MGN neuron has a favorite pitch (e.g., 1,000 Hz). When that pitch plays, the neuron fires extra hard (↑ above baseline). Neighboring Frequencies (The "Surround") Frequencies slightly higher or lower (e.g., 900 Hz or 1,100 Hz) make the neuron fire less (↓ below baseline). This creates a contrast boost for the preferred pitch, like a spotlight in fog. "Edge Detection" for Pitch Some MGN neurons specialize in detecting sudden changes in frequency (e.g., a sliding whistle or vocal inflection). Helps you notice transitions in speech/music (like "wa" → "ba")

Question 32

The primary auditory cortex A1

Answer 32

Close neuroanatomical proximity to speech areas Many types of cells coding the presence (on) or absence (off) of auditory information Cells also code the transient (fast sounds) and sustained (ongoing) properties of auditory events Similar cells are found in the primary visual cortex (V1)

Question 33

The Representation of Pitch and Loudness (Ohm's Acoustical Law)

Answer 33

High frequency waves reach their maximum amplitude near the wave source; lower frequency waves reach their peak amplitude farther from the wave source (Ohm’s Acoustical Law)

Question 34

how does the auditory system code frequency?

Answer 34

The auditory system codes frequency by the location of maximum hair cell activation on the Organ of Corti

Question 34

The Place Theory of Pitch Perception

Answer 34

The frequency of a sound is coded by the location of peak amplitude on the basilar membrane (Bekesy, 1960) High frequency sounds reach their peak amplitude near the oval window (entrance); low frequency sounds reach their peak amplitude nearer the apex of the cochlea

Question 35

How is the frequency organized

Answer 35

Frequency is tonotopically represented; neighboring frequencies give rise to activity in neighboring neurons

Question 36

The frequency theory of pitch perception

Answer 36

The frequency of a sound is coded by the firing rate of all hair cells on the basilar membrane, not just those at particular locations (phase locking) ex.If a 100 Hz pressure wave stimulates the basilar membrane, hair cells will fire at 100 Hz. Similarly, a 500 Hz tone will cause 500 Hz neuronal firing Accounts for gaps in Place Theory (e.g., why we discriminate very close low frequencies better than Place Theory predicts). Place Theory vs. Frequency Theory Place Theory: High pitches = hair cells near the cochlea’s base vibrate. Frequency Theory: Low pitches = hair cells fire in time with the sound wave. Combined: Your brain uses both for full pitch range!

Question 37

Problems with frequency theory

Answer 37

Neurons can’t fire faster than about 1000 Hz; how then are high-frequency sounds coded? If firing rate is coding pitch, how then does the auditory system code loudness?

Question 38

The place-frequency theory

Answer 38

The auditory system uses both place (location on the basilar membrane) and frequency (firing rate) to code a sound’s pitch „ Tones < 500 Hz are coded by frequency, not place; tones > 500 Hz are coded by place, not frequency. „ For tones < 500 Hz, loudness is coded by the number of cells firing; for tones > 500 Hz, loudness is coded by the firing rate

Question 39

hearing loss

Answer 39

Conduction Loss „ Damage to the outer or middle ear results in sound energy being poorly conducted or transferred to the inner ear „ Neuronal Loss „ Damage to the inner ear (the hair cells or spiral ganglion cells) or the auditory cortex

Question 40

causes of conduction loss

Answer 40

Ear wax build-up „ Middle ear infection „ Otosclerosis „ Stapes becomes immobile; can be treated surgically

Question 41

causes of neuronal loss

Answer 41

Damage to the Cochlea or Hair Cells „ Acute or chronic noise exposure „ Exposure to certain drugs (excessive aspirin or nicotine) „ Damage to Auditory Nerve „ Infection or trauma „ Presbycusis „ Age related loss of sensitivity to high frequencies sounds