Lecture 11 Flashcards
In the minimal audible pressure for TDH, why is there a difference between that and inserts?
Inserts in ear canal don’t get transfer function of the outer ear. Due to the transfer of energy in ear canal.
Our dynamic range is about 120dB but is frequency dependent.
dB HL same as dBSPL.
What is intensity? What is loudness?
Intensity is a measure of sound pressure (units dB SPL); loudness is a measure of the perception of sound pressure (units phons and sones)
What is a phon?
dB SPL of a sound perceived to be equal to a 1000Hz tone at a specific dB SPL (always in reference to this frequency)
Reference to a certain stimulus.
For example, take a 1000Hz tone, take another tone at frequency above 1000 (2000Hz), how loud is it relative to the 1000Hz tone; raise 1000Hz up to equal level of other tone.
Whatever intensity that 1000Hz is, it is equally loud as sound given from 2000Hz, that is its’ phon level.
Is a measure of loudness. Every 10dB up = increase by about 10dB phon =>double perception of loudness.
What is a sone?
Ratio of loudness for one sound relative to the loudness of a 1000Hz tone presented at 40dB SPL.
40 phons = 1 sone; sound equally loud to 40dB SPL 1000Hz tone.
Ex. 40-50dB = 1 to 2 sones
40-60dB = 2 to 4 sones
(Every 10dB up = 2x as loud)
What is an example of a phon?
A 100Hz tone presented at 50dB SPL is percived to be as loud at a 1000Hz tone at 40dB SPL. Thus, the 100Hz tone is said to have 40 phons of loudness.
What is the schematic for the loudness model?
Sound input > filter transfer to eardrum (outer ear and ear canal) > filter for transfer through middle ear (middle ear transfer function > mechanical, electrical, chemical, electrical of action potentials > Central auditory processing > loudness perception
What is the loudness model considering binaural inhibition?
How is this important for the perception of sound?
For 2 working ears - one can inhibit the other - binaural inhibition and masking effects
LE and RE come in, calculate inhibitory function - loud sound in RE, inhibits sound perception of LE (vice versa)
With inhibitory function (some calculations) you get loudness
Perception of sound is an integration of pieces of loudness over time, incorporate binaural and summing of activity over time
Why in the audiogram is a 2 second beep used?
Because short tones contain all the frequencies - might get a positive response and wouldn’t be responding to correct tone. Short tone needs higher energy sometimes to activate if you are near threshold, even in spectral issues.
Only 200-250ms - dealing with short amount of time (wouldn’t hear beep unless you have a lot of spectral splatter) - tradeoff. Shorter tones, you need higher intensity.
Why is loudness perception important for the auditory system?
Why is this important for Audiologists/SLPs?
It is how our basilar membrane mechanics work; central stuff (learning, don’t know everything)
How it gives us perception of loudness, how to deal with masking - what happens, how does that deal with loudness of voice…ex. back of the room with fans on.
Audiology: What is the MCL in the classroom, how audible/loud is it - perception.
SLP: Need individuals to produce loudness, someone to project their voice loudly so other people can hear, and we can communicate, especially if they have a hearing loss.
What are the various stages in an auditory nerve firing, based on intensity?
No stimulus
Less intense stimulus
More intense stimulus
What is the minimum threshold for the entire auditory system?
No stimulus - spontaneous firing because of release of NT - trap doors open slightly, some depolarization/hyperpolarization; homeostasis (25dB SPL - minimal threshold for entire auditory system)
Less intense stimulus - increasing frequency of action potential firing due to change in stimulus (detected) - above 25dB SPL rate increases to certain % above to reach threshold
More intense stimulus - increase in firing rate = code; depends on rate of nerve fibre’s firing; increased intensity means higher/greater discharge rate, then plateaus
Why does the auditory system mainly exist?
To detect change
What is the dynamic range problem?
Can’t code for all of the frequencies with the 120dB range - can’t do this with a single nerve fibre. Need many fibres and as per loudness perception models, we have many other processing after nerve fibres, also explains this problem.
No info below 25dB for spontaneous rate, no info about level above 60dB SPL
Certain discharge rate for auditory nerve fibres - can tell by output of nerve fibre and get an indication of what stimulus intensity came in (codes for it in certain range)
How does intensity coding work by the auditory system?
Single fibre can code only 30–50dB range (whole system has 120dB range)
Number of fibres responding (spread of activation along BM may also be a code for level)
Nerve fibres have different spontaneous rates with lower to higher threshold - shifter to higher as dB SPL decreases.
Recruitment plays a role - how many nerve fibres are activated?
What role do specific intensities play in the intensity coding for the auditory system?
Low spontaneous rates need a lot of energy to move…slow (take a lot more to get going)
When all fibres are firing, coding happens by rate of firing = all at high intensity and spectral spread because BM then gets wider and wider range.
Intensity coding when going up in spread and frequency. It a large portion of nerve fibres really activated, all saturated, probably at high intensity at that frequency.
What happens when the cochlea is damaged in the system of intensity coding in the peripheral auditory system?
If the OHC are damaged, they stop adding energy - not the same intensity. Nerve fibres don’t respond in the same manner, not getting activated by OHC at low intensities; not getting recruitment across the BM or any improvement on spontaneous rate fibres.
At low intensity sounds you are not getting amplification to the OHC = Hearing loss.
