Audition - Part 2

What causes an object to vibrate? What varies about an object?

An initial force must be imparted on the object

The natural frequency will vary in each object, which is determined by the mass and stiffness of the object

What is the natural frequency?

The natural frequency of a system is the frequency at which an object responds the best, resulting in the largest vibration

Describe frequency selectivity as it relates to the input and output signal

The closer the frequency of the input signal to its natural frequency, the higher the output will be

Different systems are more responsive to different input frequencies - frequency selectivity

When pushing a swing, what will not affect the frequency and what are the factors that will?

No matter how you push, the frequency will be the same (the force that you apply to the swing will not affect the frequency)

Frequency is determined by the length of the robe and the mass of the girl

What are the three components of impedance?

Stiffness, mass, friction

How are stiffness, mass and friction related to frequency?

The stiffness component decreases with increasing frequency, the mass component increases with frequency. The friction component does not change with frequency

What are the formulas for stiffness, mass and friction?

1. Xm=2πfm

2. Xc=S/2πf

3. sum of mass and stiffness component

What is reactance?

Reactance is the contribution of mass and stiffness to impedance. The sum of the mass and stiffness components represents the total reactance.

Which components are in opposing phases (i.e. 180 degree difference)

The mass and stiffness components

When does natural frequency occur as it related to the three components?

The natural frequency occurs when the mass and stiffness components are equal (they cancel each other out)

What is a one sentence definition of frequency selectivity/frequency response?

Frequency response is how gain changes with frequency. It is gain as a function of frequency

What is damping? What is light versus large damping?

Damping refers to the effect of friction on a vibrating system. The amount of time a system will vibrate for depends on the damping on the system.

Light damping - less friction (vibration will last a long time)

Large damping - more friction (vibration will stop sooner)

What is the friction effect as it relates to damping?

low friction = smaller damping, higher friction = larger damping

What is the friction effect as it relates to BOTH damping and frequency selectivity?

Low friction: light damping, good frequency selectivity

High friction: large damping, poor frequency selectivity

What is the relationship between a system's frequency selectivity and temporal resolution? How does this relate to the ear (briefly)?

A system with high frequency selectivity usually has a poorer temporal resolution and vice versa

In hearing, we want good frequency selectivity and good temporal resolution, so the cochlea works to achieve this

Note: temporal resolution refers to how quickly we are able to hear and process the input stimuli around us

All tied together with idea of damping

If you have more damping, you have better temporal resolution but worse frequency selectivity, this is like a trade off but we need both to be good in the auditory system and the cochlea tries to do this

What is the general ratio measured by gain? What is the formula as it relates in decibels to sound?

Gain = output/input

Gain (dB) = 20log(P2/P1)

What is the calculation to measure gain in terms of intensity?

10log(I2/I1)

What is the formula to equate the intensity of sound to the decibel pressure measurement of sound?

I = kP2

In the formula, when there is P2 or I2, is that measuring the input or the output? What is an example of where the input or output could be measured as it relates to the ear?

P2 or I2 refers to the output signal. Remember, gain = output/input!

In relation to the ear, we could measure how much sound is getting to the eardrum from the ear canal entrance. The measurement at the eardrum would be the output, and the measurement at the ear canal entrance would be the input.

Explain how the external ear acts like a tube in relation to resonant frequency?

The external ear can be considered as a tube closed at one end (as we previously discussed, it is the tympanic membrane that seals the ear canal).

When air particles are vibrated by sound of various frequencies, the greatest amplitude is seen at the natural frequency (resonance).

What is the standard length of the ear canal?

26mm or 2.6 cm

What is the formula for resonant frequency for the external ear?

F = n c / 4 L

The external ear resonance is based on the average gain of which 3 parts?

Flange, concha, meatus

Which part of the external ear has the largest contribution to the overall gain?

meatus (ear canal)

What is the overall gain at the average ear canal resonance?

Overall gain is amount of gain from all of the curves added together

Around 15 dB

Which of the three parts/areas has a peak at a lower frequency relative to the other two parts? Which has the highest?

The meatus has a peak at the lowest frequency and the concha peaks at the highest frequency

What is the approximate resonance frequency of the whole external ear?

Approximately 3200 Hz

This is the resonant frequency of the external ear

How does resonant frequency change with age? At what approximate age do we see that it is closer to our 'adult' frequency? What is the (general) reason for this?

As we age, our resonant frequency gets lower because the ear canal gets longer. At 37 months, our resonant frequency reaches our "adult" frequency.

What is the second function of the external ear canal?

Provide cues for sound localization

What are the two categories of external ear canal sound cues?

Spectral and binaural cues

What term is transfer function similar to?

Frequency response

What is another name for the pinna effect?

Spectral cues or pinna cues

What are the three ways the external ear protects the eardrum?

The irregular shape (S configuration, cerumen, and hairs)

What are three 'protective' components inside the ear canal? What fraction of the ear canal has these (laterally/medially)?

The three protective components inside the ear canal are hairs, sebaceous glands, and ceruminous glands

The lateral 1/3 of the canal has these components

How many degrees is the tympanic membrane angled with reference to the axis of the canal? What purpose does this serve?

TM is in a 45 degree with the axis of the canal

Functions to reduce the impact of it being hit by a foreign body

What is the average length of the ear canal in cm? What is the average diameter?

Length = 2.6 cm

Diameter = 0.7 cm

What is the self-cleaning mechanism of the ear canal? (What is another name for this)

Epidermal migration - the slow growth of cells and the migration of them push debris out of the ear canal

What is another name for the eardrum?

Tympanic membrane

Which view (lateral or medial) can we see the two parts of the eardrum?

Lateral

What are the two main parts of the ear drum?

Pars flaccida and pars tensa

How many layers do the pars flaccida and pars tensa have?

Pars flaccida: two layers (no fibrous layer)

Pars tensa: three layers

What kind of layers do the pars flaccida and pars tensa have?

Lateral: cutaneous (epithelial)

Center: fibrous

Medial: mucous (serous)

What are each of the layers connected to (pars flaccida and pars tensa)?

Lateral: connected with the ear canal

Medial: connected with the middle ear cavity

What purpose does one not having the fibrous layer serve?

The pars flaccida doesnt have the fibrous layer so it is more flexible and serves as an air pressure buffer

Note: the pars flaccida does not attach to the bone chain and is therefore NOT responsible for sound conduction

Describe the tenseness of one relative to the other?

The pars tensa is stiffer

Which one is thicker, pars tensa or pars flaccida?

The pars flaccida

Which one is dorsal to the other? What is at the border between the pars tensa and pars flaccida (which nerve and which ligament)?

Pars flaccida is dorsal

Annular ligament and chorda tympanic (a branch of the facial nerve) are at the border between the pars tensa and pars flaccida

What is one technique to tell which ear it is based on the tympanic membrane?

Either looking at the cone of light or the long process of the incus

Why is there a cone of light?

When we examine the tympanic membrane with an otoscope, we're shining a light into the ear canal. The cone of light is a reflection of the light from the otoscope. It is always in the same position due to the shape of the tympanic membrane.

What is the more known nerve that the chorda tympani is part of? What is its main role?

Facial nerve

The role of the chorda tympani is to carry taste from the ipsilateral half (same side) of the tongue

What does manubrium mean?

Handle

What does the manubrium attach to?

Tympanic membrane - umbo

Describe the rotation of the eardrum in relation to the bone chain. (Which part of the eardrum has the largest vibration)

The connection between the malleus and incus makes the 2 bones work like a lever. The malleus and incus are rotated around its pivot, causing the eardrum to vibrate unevenly. The largest vibration is on the inferior part of the eardrum.

What are the four main parts included in the malleus?

Head, neck, lateral process and manibrium

What are the 4 main parts of the incus?

body, short process, long process, lenticular process

What are the four main parts of the stapes?

head, neck, anterior and posterior crus, footplate

When the stapedial footplate rocks, where is the ligament attachment stronger at? Which side is free to move?

The ligament attachment is stronger at the posterior point, and the larger movement is at its anterior part

What is the model for the middle ear based on its shape?

Cubic box

What wall are the mastoid air cells located?

The posterior wall

What are the 4 parts in the posterior wall? (What is another name for this wall)

Aditus antrum, pyramidal eminence, incudal fossa, chorda tympanic nerve entrance. Another name for this wall is mastoid wall

What are the 5 parts in the medial wall? (What is the other name for this wall)

Labyrinthine wall. Parts: round window, oval window, facial nerve canal, prominence of lateral semicircular canal, cochlear promontory

What is a characteristic of the superior wall? What is another name for this wall?

Tegmental wall. Characteristic: it has an epitympanic recess (attic) which provides space for heads of malleus and incus

What is a characteristic of the inferior wall? What is another name for this wall?

Separates the ME from the jugular bulb below. Also called the tympanic wall

What is the lateral wall?

The tympanic membrane

What are 3 landmarks located at the anterior wall?

Tensor tympanic tendon/muscle entrance

Eustachian tube orifice (opening)

Internal carotid canal

What is the general definition of a ligament?

Ligaments are elastic tissue which connect bones to other bones

How many ligaments are/is there connected to the malleus? What are/is they/it?

3: superior, lateral and interior

How many ligaments are/is there connected to the incus? What are/is they/it?

1: posterior

How many ligaments are/is there connected to the stapes? What are/is they/it?

1: annular ligament