Inner Ear 2... (Filters, Active process) Flashcards
Envelope
- the point along the basilar membrane that is frequency-selective
- has to do w/ resonant properties
- corresponds to peak displacement
Travelling wave
- tail is shallow and long
- wavefront is steep and short
- upward spread of masking
Upward Spread of Masking
- 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
4 Types of Filters
- Low pass
- High pass
- Band pass
- Band reject
Low pass filter
- passes low freqs thru
- attenuates high freqs
High pass filter
- passes high freqs thru
- attenuates low freqs
Band pass filter
- combines low and high pass filters
- passes freqs within a certain range
- attenuates freqs outside that range
Band reject filter
- passes most freqs
- attenuates those in a specific range to very low levels
- opposite of band pass
Filter skirt
- the slope of a band pass
- steep slope = anything digital can be cut off
- gradual slope = required by analog filter
Cochlea acts as a _____
Bank of band-pass filters
- if we put a signal in, the envelop acts as a band-pass filter
Von Bekesy’s opinion on BM Vibration
- linear, related to gain
- whatever you put in, you get a predictable, fixed amount out
Rhode’s opinion on BM vibration
- nonlinear, more gain for less input
Why the difference in opinion btwn VB and Rhodes?
- VB used cadavers
- Rhodes used live animals
BM Input/Output Function
- 9000 Hz Characteristic frequency (Cf)
- BM nonlinear near cf (true around freq of stimulating signal)
- linear far from cf (1000 Hz)
Critical Band
- 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!
The _____ of the filter is a function of the ______ of the ear
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)
The active process involves 3 things:
OHCs
IHCs
Shearing of hair cells
OHCs role in the active process
- 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)
OHCs ________ in response to sound
- stretch and shrink!
OHCs innervated by _______
- olivocochlear bundle
Evidence of the OHC active process
- tuning curve
IHCs role in the active process
- without IHCs we have no hearing = signals will not be transmitted to the brain
(afferent fibres) - cannot pick up sounds below 50 dB SPL
IHCs innervated by _____
CN VIII (vestibulocochlear)
Shearing of hair cells
- 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
Effects of this Active Process
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
