Hearing (wk 6)

Question 1

What is the principle of sound conduction?

Answer 1

An oscillating object will cause air to become more and less dense: compression and rarefaction

Question 2

What is the wavelength equation?

Answer 2

wavelength = velocity/ frequency

Question 3

What is sound amplitude?

Answer 3

Sound amplified is generally expressed as a ratio: . The ‘standard’ is the mean hearing threshold: 10-12 Wm-2 (watts x square metre). Corresponds to 10-11m movement of air molecules: less than diameter of hydrogen atom.

Question 4

Describe the range of human hearing:

Answer 4

-0 is an auditory threshold. The older you get, the larger the frequency becomes – towards 20,000 Hz.
-Lower sensitivity to low frequencies -> Sometimes, sound pressure levels are adjusted using the ‘A weighting’. This effectively down-scales low frequencies to acknowledge our lower sensitivity.

Question 5

Describe age and hearing loss

Answer 5

-Age and hearing loss: presbycusis. As you get older you start to lose frequency in hearing which turns into hearing loss. Usually the older you get, the worse it becomes.

Question 6

Describe the frequency of sound - 20Hz to 20 kHz (ten octaves)

Answer 6

• Low bass (20 to 80 Hz) includes the first two octaves (bass, tuba)
• Upper bass (80 to 320 Hz) includes the third and fourth octaves (cello, trombone)
• Mid-range (320 to 2,560 Hz) includes the fifth through seventh octaves (guitar)
• Upper mid-range (2,560 to 5,120 Hz) is the eighth octave
• Treble (5,120 to 20,000 Hz) includes the ninth and tenth octaves

Question 7

What are the role of ossicles (middle ear(:

Answer 7

-> Middle ear acts as a lever. Converts high amplitude/ low force motion at ear drum into low amplitude/ high force motion at oval window. Impedance matching. The sound moves the bones and in turn moves the column of fluid backwards and forwards through the brown window. This allows the fluid to bulge and create movement.

Question 8

Describe the stapedius reflex: two muscles act on ossicles:

Answer 8

-> Contraction of these muscles pulls stapes away from oval window. Decreased transmission of vibrational energy to cochlea. Stapedius reflex occurs in response to very loud sound. Also occurs during speech. Crucial for preventing hearing damage. Useful for protecting hearing for moderate and very loud sounds. Pulls stapes bone away from window so soften the sound.

Question 9

Describe the cochlea - inner ear:

Answer 9

-Round window is free to move. Sound enters the scalae vestibuli and goes to the helicotrema and then goes into the scalae tympani which allows the sound to bulge and move. In the inner ear, it is set up like a coil to be space efficient.

Question 10

Describe the organ of corti and hair cells:

Answer 10

-Basilar membrane separates the 2 scalae. The membrane is flexible and allows movement, allowing the sound to and fluid to move around.
-Small up-down movements of the basilar membrane cause a large relative shear of the tectorial membrane, thus activating the hair cells.
-Hair cells -> Inner hair cells are responsible for sensation. The basilar membrane moves and allows the inner hair cells to deflect.

Question 11

Describe pitch place theory:

Answer 11

-> George von Bekesy. Different areas of basilar membrane can detect different sound frequencies. If you are able to use invasive methods to identify how different areas correspond to different sounds and frequencies and discriminate the different frequencies. The waveforms are oscillating at different sounds.

Question 12

What is the motion of basilar membrane?

Answer 12

Replication of the pitch place theory through the pitch place theory.

Question 13

Describe the ear as a fourier analyser:

Answer 13

-> Any waveform can be decomposed into sine waves of various frequencies. Even a square wave can be made up of sine waves. Combine the fundamental frequency with progressively smaller harmonics. It decomposes time-based sound signals into their frequency components.

Question 14

What is the sharpening of the tuning curve?

Answer 14

-> Tuning of hearing is far more sharp than explained by the passive mechanics of the basilar membrane alone. Sharpening of response curve of ear to scale of observed pitch resolution. Some amplification must be happening.

Question 15

What are inner and outer hair cells and the process of them?

Answer 15

-Inner and outer hair cells -> There is movement of outer hair cells through the protein – prestin.
1.The ‘active undamping’ by the outer hair cells is an example of a positive feedback loop.
2.Outer hair cells can generate sound -> Otoacoustic emissions are ‘echoes’ in response to clicks delivered to ear. Absence indicates problem of inner ear. Used to assess hearing in newborns. Possible mechanism of some (but not most) types of tinnitus.

Question 16

What is hearing sensitivity?

Answer 16

-> Is a combined damage through level and duration of the sound. Anything over 85 dB is potentially damaging.

Question 17

Describe the auditory pathway to the brain and sound related brain activation:

Answer 17

-> Sound activates many areas from cochlear nerve to auditory cortex. Includes superior olive (brainstem). Sound-related brain activation uses the EEG.
* Broca’s speech area ‘expressive’
* Pitch/rhythm
* Inferior olivary nucleus -> Inter-aural differences in loudness and timing
* Wernicke’s speech area -> Receptive
* Broca’s area damage -> Talk but not able to understand what they are saying

Question 18

What is distance and bearing?

Answer 18

-Distance -> range
-Bearing -> azimuth and elevation

Question 19

Describe judging distance:

Answer 19

• High frequencies travel less well; far-away sounds dominated by bass
• Expectation (e.g. intensity of voice)
• Relative attenuation (timbre) (bass travels best, sibilants worst)
• Echoes (multiple echoes – reverberation-less attenuation)

Question 20

Describe judging direction:

Answer 20

• Inter-aural timing/phase differences
• Inter-aural volume differences
• Spectral colouring (by head and pinna)

Question 21

Describe inter-aural volume differences (ILD) (better for high frequencies)

Answer 21

• The head provides a sound ‘shadow’
• Attenuates volume in ear opposite sound source
• Greater attenuation for high frequency sounds
• Hence, far away speech more bassy (vowels emphasised, sibilants attenuated)

Question 22

Describe inter-aural timing differences (better for low frequencies)

Answer 22

• Inter-aural time delay (ITD) -> A click from the left will arrive at the left ear first, then right ear soon after

Question 23

What is Jeffress theory of Inter-aural time delay (ITD) detection?

Answer 23

-> Neurons in superior olive (brainstem) act as coincidence detectors. When action potentials arrive simultaneously from both ears, MSO neuron more likely to fire. Relies on differing lengths of axons. Provides a neuronal map of sound location.

Question 24

Describe inter-aural phase differences:

Answer 24

-> If sound is a continuous tone, use phase difference to localise. Not very useful when wavelength is shorter than the head (i.e. high frequency sound). L-R difference of 360 degrees sounds the same as 0 degrees – ambiguous.

Question 25

Describe head size and cone of confusion:

Answer 25

-Head size -> Big head -> large L/R time difference. Small head -> not much L/R time difference. Big head uses timing differences and a small head mainly uses loudness differences.
-Cone of confusion -> Sound emanating from different locations can produce identical ILD and ITD profiles at the two ears. Example – sounds emanating from behind can sometimes sound in front of the head. Tilting and turning the head alters the cone of confusion.

Question 26

What is spectral colouring by pinna and head?

Answer 26

-> The outer ear (pinna) attenuates sounds from certain directions, amplifies sound from others. Invisible to low frequency sounds (bass). Therefore, the spectral content of sound combined with prior experience, can be used for localisation.

Question 27

What is binaural recording?

Answer 27

-> High-fidelity recording studios often use binaural microphones. Mimics inter-aural differences in humans. Produces a more pleasing sound.

Question 28

What are animal calls?

Answer 28

-> Sounds with a narrow band of frequencies and gradual onset and offsets are hard to localize. Use brief, high-frequency sounds without sharp onsets to avoid localization. Use longer, more intense, broadband sounds to attract attention.

Question 29

What is the auditory reaction time?

Answer 29

-> Typically 140-160ms. Visual RT slower (180-200ms). Sound takes about 3ms per metre.