Hearing Science Exam 2

The two functions of the pinna

Funneling sounds: increase surface area (As you move farther away from a sound source, the same intensity is going to have to cover a lot more area so any given region “square” is going to have less sound intensity as you move far away; overcome by having a bigger receiver [pinna])

Filtering sounds: changing the level of certain frequencies

Purpose of the Pinna’s irregular shape

makes it possible to determine the elevation and front/back location (localization) of a sound source

Sound Localization

the process by which we locate sounds

List the two main cues to locate objects and their limitation

Interaural level and time differences (ILD and ITD); These only give us left-right information– they don't tell us anything about whether the sound is high, or low, or in front or behind us

Head Related Transfer Function (HRTF)

The head and ears filter sounds differently depending on where they come from; how we localize sound in the median plane where ITD and ILD don’t work

Median Plane

the vertical _____ that divides your body into left and right halves; In hearing, sounds in the ____________ come from directly in front, behind, above, or below you, so both ears get the same sound at the same time (so ITD and ILD can’t help here)

What happens when sound bounces around the pinna? 

It destructively interferes with itself at certain frequencies; acts like a filter with a _____ notch at around 10kHz (The frequency and “depth” of changes with elevation, giving us cues for localization); When the sound is coming from the front, the interference is much greater 

List the function(s) of the ear canal

Acts like a tube and amplifies certain frequencies because it has resonant frequencies; Protects the eardrum (from foreign bodies and changes in temperature and humidity) – hair and cerumen (ear wax); has cleaning action and can repair TM perforations

List the important characteristics of the ear canal

outer ⅓ is cartilage (has hair, glands to produce cerumen (wax) to protect ear against certain bacteria) ; inner ⅔ is a bony portion (lined by thinner skin and more sensitive)

Describe the filtering action of the ear canal.

The _____ ______ resonance boosts the signal at frequencies that match/near the resonant frequency; Has a different pressure than the one in the sound field because of the _____ _____ of the _____ _____

What is the transfer function and what does it represent?

The pressure level difference “gain” you get from going from one place to another; Gain vs. Frequency

Gain

The increase is sound pressure level from point A to point B at any one frequency; Different for each frequency

What is the tympanic membrane? What are the parts and function?

The eardrum; Parsa tensa (outer thin skin layer; fibrous layers; inner mucous layer) and parsa flaccida (thin and lax, no fibrous layers); Converts sound waves in air to vibrations in the bones attached to it

The ______  separates the external ear from the middle ear

Eardrum

What are the three parts of the middle ear?

Ossicles, Eustachian tube, Tensory Tympani and Stapedius Muscle

What are the six walls of the middle ear?

Lateral, medial, superior, inferior, anterior, posterior

Function of the ossicular chain? 

Form the coupling between the vibration of the eardrum and the forces exerted on the oval window of the middle ear; act as a mechanical lever system take the vibrations from the eardrum (caused by sound waves in the air) and amplify them before passing them to the oval window of the cochlea; matches the impedance and protects sensory (hair) cells

Impedance Matching

Impeding/stopping the flow of something; There is an impedance boundary, air and fluid are not in the same medium + higher impedance of fluid will cause most of the sound to be reflected;  prevents loss of sound energy by amplifying sounds between air and fluids of the cochlea; done through area ratio (25 dB increase) and lever action (malleus and incus; 2 dB increase)

How do the tensor tympani and stapedius muscle prevent damage 

Through the acoustic reflex; If sounds are too loud the lever can be “adjusted” by muscle action to attenuate the sound for protection against damage

Acoustic Reflex

Muscles contract and increase the stiffness of the ossicular chain, reducing the sound that gets through to the inner ear (mainly attenuates (reduces) low-frequency sounds); frequency=root(kstifness/mass)

Reflex latency

Time it takes to kick in; Acoustic reflex may be too slow to protect from impulse noise

How does the Eustachian tube equalize pressure? 

Connects the middle ear to the nasopharyngeal of the throat “opens” with swallowing or coughing to _____ ______ between the middle ear and ambient pressure in the throat