Inner Ear 2... (Filters, Active process)

Question 1

Envelope

Answer 1

• the point along the basilar membrane that is frequency-selective
• has to do w/ resonant properties
• corresponds to peak displacement

Question 2

Travelling wave

Answer 2

• tail is shallow and long
• wavefront is steep and short
• upward spread of masking

Question 3

Upward Spread of Masking

Answer 3

• if you take a low freq sound and make it louder, it increases the envelope of the BM closer to the start, and can mask a higher freq signal that is softer
  E.g.
• high intensity, Low Hz, masks High Hz
• High Hz doesn’t mask low Hz, no matter the intensity
• if you have high intensity, Low Hz, it will travel all the way to the apex

Question 4

4 Types of Filters

Answer 4

1. Low pass
2. High pass
3. Band pass
4. Band reject

Question 5

Low pass filter

Answer 5

• passes low freqs thru

- attenuates high freqs

Question 6

High pass filter

Answer 6

• passes high freqs thru

- attenuates low freqs

Question 7

Band pass filter

Answer 7

• combines low and high pass filters
• passes freqs within a certain range
• attenuates freqs outside that range

Question 8

Band reject filter

Answer 8

• passes most freqs
• attenuates those in a specific range to very low levels
• opposite of band pass

Question 9

Filter skirt

Answer 9

• the slope of a band pass
• steep slope = anything digital can be cut off
• gradual slope = required by analog filter

Question 10

Cochlea acts as a _____

Answer 10

Bank of band-pass filters

- if we put a signal in, the envelop acts as a band-pass filter

Question 11

Von Bekesy’s opinion on BM Vibration

Answer 11

• linear, related to gain

- whatever you put in, you get a predictable, fixed amount out

Question 12

Rhode’s opinion on BM vibration

Answer 12

• nonlinear, more gain for less input

Question 13

Why the difference in opinion btwn VB and Rhodes?

Answer 13

• VB used cadavers

- Rhodes used live animals

Question 14

BM Input/Output Function

Answer 14

• 9000 Hz Characteristic frequency (Cf)
• BM nonlinear near cf (true around freq of stimulating signal)
• linear far from cf (1000 Hz)

Question 15

Critical Band

Answer 15

• measure threshold to pure tone w/o masker
• add noise masker
• threshold goes up
• cut out a notch of noise
• as the notch widens, the threshold will start to come back down
• when the threshold no longer decreases, the width of the notch = the width of the auditory filter for that sound
• this is how we know auditory filters are a real thing!

Question 16

The _____ of the filter is a function of the ______ of the ear

Answer 16

The WIDTH of the filter is a function of the HEALTH of the ear

• impaired ears have broader filters (too many other sounds trying to get in when listening… masks the signal they’re trying to hear)

Question 17

The active process involves 3 things:

Answer 17

OHCs
IHCs
Shearing of hair cells

Question 18

OHCs role in the active process

Answer 18

• amplify sounds below 50 dB SPL
• sharpen travelling wave peak
• do not do the hearing, they do the CONDUCTION
• efferent fibres (receive messages FROM the brain)

Question 19

OHCs ________ in response to sound

Answer 19

• stretch and shrink!

Question 20

OHCs innervated by _______

Answer 20

• olivocochlear bundle

Question 21

Evidence of the OHC active process

Answer 21

• tuning curve

Question 22

IHCs role in the active process

Answer 22

• without IHCs we have no hearing = signals will not be transmitted to the brain
  (afferent fibres)
• cannot pick up sounds below 50 dB SPL

Question 23

IHCs innervated by _____

Answer 23

CN VIII (vestibulocochlear)

Question 24

Shearing of hair cells

Answer 24

• cell responds to a tip deflection, less than the diameter of a hydrogen atom!
• equivalent to a movement that would displace the peak of the Eiffel tower by 1cm

Question 25

Effects of this Active Process

Answer 25

Large dynamic response range

• > low intensity sounds amplified
• > above 20 dBSPL, amount of amplification declines until 90 dBSPL
• > above 90 dBSPL, no additional amplification occurs (BM & IHCs are on their own)
• > if you didn’t have OHCs you wouldnt hear anything soft

Generation of sound w/in cochlea

• > spontaneous otoacoustic emissions (SOAE)
• > evoked otoacoustic emissions (EOAE)
• —> if you don’t have these, your OHCs aren’t moving