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CMSD5280 Audition ll > Cochlear Physiology IV: Auditory Nerve part 2 > Flashcards

Cochlear Physiology IV: Auditory Nerve part 2 Flashcards

1
Q

What is occurring in this graph?

A

This is the Phase locking in Volley principle by Wever
It shows the integration of different neurons, makes Phase locking better

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2
Q

What does this graph demonstrate?

A

This graph is the response to low-frequency tones: phase locking
Phase locking is a temporal feature of neurons that can be seen when the frequency is low (low-frequency tones). We can see the periodicity of the response v.s the periodicity of the signal (graph 2)

Higher frequency neurons, can record low/high? frequency signals by phase locking

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3
Q

What is the ISIH?

A

The second method to show the Temporal Pattern
ISIH: Interspike interval histogram
The time axis divided into equal time bins
Does not refer to stimulus onset, but to intervals between spikes, the neurons must respond in intervals.
Due to phase locking, spike interval is not a random event, rather more chance appears at certain interval values
Integer relationship among peaks
Multiple presentations show the trend

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4
Q

What is the PRH?

A

PRH—period histogram
The time axis divided into equal time bins
Only shows several periods or cycles.
Spikes counted in each time bin for many presentations of the stimulus
Shows periodicity or phase locking of the firing pattern

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5
Q

So far, we only describe phase locking of signal tones, what is the other type of signal where phase locking can occur?

A

Complex signals can get phase locking as well: We call it temporal envelop

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6
Q

How does PL occur with Complex Signals (two tones low or high frequencies)?

A

When we use two tones (second easiest to measure), we use it to measure how neurons code temporal patterns Two tones of high f (small diff) neurons will phase lock to the beats

  1. We use two tones of low frequencies
  2. Phase locking occurs to
    First tone
    Second tone
    Both
  3. Phase locking to beat
  4. Complex signal
  5. Phase locking occurs in the temporal envelope
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7
Q

What does this graph show (Related to Complex Signals)?

A

This graph shows Phase locking to two tones combinations: Response showing across time
Phase locking can occur in individual tones
When we combine the two tones of different phases (phase difference) The shapes of the spikes will be different, phase locking to the envelope

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8
Q

What does this graph show?

A

This graph shows the response to complex tonal stimuli: phase locking to envelope

Graph A: The thin line shows envelop that is not modulated (equal amplitude) envelop is even. With the thick lines, it shows modulations of amplitude (AM) showing the difference in phase locking to the envelope -dashed curves show the envelope.

Graph C: The equal time interval of 10 ms between the main peaks PSTH and the peak interval in the envelope of amplitude-modulated sound. This indicates that the response is phase-locked to the envelope of the AM signal. If the fine structure is low enough you will see phase locking - PSTH of the neurons follows the envelope of the sound.

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9
Q

What does this graph show?

A

The envelope has slow temporal cues
Important information carrier
Encoding in cochlear implants

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10
Q

What does this graph show?

A

Phase locking to the envelope of the complex signal of a guinea-pig

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11
Q

Where is the first limiting site for temporal processing in the inner ear? Why?

A

The first Limiting site is at the synapse, not the transduction site because the release takes time (time delay) because it’s not electrical its biochemical (NT)

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12
Q

What is the role of the Ribbon in Presynaptic Synapse? (3)

A

Facilitates faster release and recycling by:

  1. Ribbon structure facilitating NT release
  2. Postsynaptic receptor (not known if special) GluR
  3. Recycling of neurotransmitter
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13
Q

Give a quick summary of cochlear temporal coding: (3)

A
  1. Phase locking and temporal pattern provide the bases for temporal coding
  2. Phase locking follows the amplitude envelope of sound
  3. There is no place code in the cochlea for temporal information
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14
Q

What does this graph show?

A

This is an example of research on speech coding based on rate code
(a) Two peaks
(b) Two peaks only at low levels
(c) Higher levels we get lost so not sure, Larger b, phase locking will play a role in high intensity
(d) Even larger bandwidth Note the loss of peaks at a high intensity (d, 78 dB)

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15
Q

What does this graph show?

A

This is the averaged localized synchronized rate
We can see clear peaks at lower levels of intensity from phase locking corresponding to the spectrum of speech

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16
Q

Give a quick summary of PL in Frequency coding: (4)

A
  1. Phase locking delivers information about the signal period, therefore it is a way of frequency coding
  2. Phase locking works for low-frequency tones and envelope of complex (high-frequency) signals if it is temporally modulated
  3. Phase locking can occur at code beats or fundamental frequency
  4. There is a missing fundamental perception of frequency without it being present in the signal (Temporal Coding)
17
Q

Give a summary of Frequency coding (Place coding, Phase Locking, Frequency coding): (3)

A
  1. Place coding works for the whole frequency range
  2. Phase locking works for low-frequency range and helps us improve frequency selectivity
  3. Frequency coding at high-intensity and high-frequency regions is not fully understood
18
Q

What observations can we see when using high-intensity signals related to frequency selectivity, psychological frequency discrimination, and phase locking? (3)

A
  1. Frequency selectivity of 8th N fiber is poorer at higher intensity, we can see a wider Tuning curve
  2. We don’t know why, even if the TC becomes wider, our psychological frequency discrimination does not go down.
  3. Phase locking may improve fre dis. at high level.
19
Q

How is the dynamic range of hearing is established by AN? (2)

A
  1. The dynamic range (behavior dynamic range = change in Sound level cause loudness perception ) of human hearing is something around 120 dB.
  2. The dynamic range of an auditory nerve fiber is typically 20-40 dB (increase in rate firing), few up to 60 dB.
20
Q

How are the gaps filled in the dynamic range? (5)

A

Different coding methods are used:

  1. Greater DR at onset
  2. Increase Dynamic Range by Threshold Distribution
  3. Sloping saturation
  4. Spread of excitation
  5. Two-tone suppression shifts rate-level function
21
Q

What can we see from this graph related to the Dynamic Range of ANF?

A

Greater DR is seen at the onset of the sound
We measure at a long time window and count the total spikes
+: shorter time window from onset peak we see a high increase
Squares: if the time window is longer we see more saturation

22
Q

What is occurring in this graph?

A

Method 2: Increase Dynamic Range by Threshold Distribution

Some low SR (SR <18/sec) neurons have higher thresholds.
They increase the distribution of thresholds
However, the number of neurons in this group is small, how can they handle the job at high intensity?

23
Q

What does this graph demonstrate?

A

This graph shows the distribution of Idealized rate-intensity functions

Different neurons have different working ranges: some respond better to low intensity some at high, put them together you have high DR, not linear though

24
Q

What is occurring in this graph?

A

The third method: Sloping saturation

25
Q

What does this graph show?

A

The fourth method is: Spread of excitation

BM vibration spreads to high-frequency areas at high intensities
More 8th N fibers will be accumulated to code intensity
Problems with this model:
Can’t explain broadband noise
Failed in exp using band rejected noise (if spreading works, response in the notch
Increase of sound level: the neurons around Cf may get saturated, however an increase in sound level will excite more surrounding neurons thus will be recruited and contribute to the spike rate

26
Q

What does this graph show?

A

The last method: Two-tone suppression shifts the rate-level function

Phenomenon due to mechanical interaction due to two sounds, If we add a second tone, with an increase of the intensity of tone two, spike rates will decrease
Tone two is shown as the bar on top in the graphs to the left

Tone B =Sweeping tone

27
Q

What does this graph show?

A

Two-tone suppression: evidence of cochlear nonlinearity
Phenomenon due to mechanical interaction due to two sounds, If we add a second tone, with an increase of the intensity of tone two, spike rates will decrease (Suppression, not inhibition)
Tone B =Sweeping tone

28
Q

Why do we say that there is a two-tone suppression, but not inhibition? (3)

A
  1. Adding a second tone may cause a decrease in the discharge rate of the first tone; as if tone b inhibited neural activity for tone a
  2. The discharge rate is reduced only if tone b is the right freq and intensity (inhibitory area)
  3. Occurs quickly (no latency)—via mechanical interaction between two tones, it occurs so quickly that there is no inhibitory circuit involved.
29
Q

What does this graph show?

A

Pane Left: Frequency tone from low to high, to high to low so it goes to the CF TWICE panels to the left.

Panel right: Sweep Tone: If the tone is low then no rate change, If it gets higher, the response to CF becomes suppressed. Lower peaks are the point where Cf and Sweeping tone merge. It is kind of a masking effect

30
Q

How does the effect of background noise affect the working range of ANFs?

A

Background noise shifts the working range of ANFs (push it up)

  • Q: quiet, all other curves having background noise as indicated by the number for the noise in the spectrum level
  • C and D are normalized from A and B respectively
  • A and C: a high SR ANF -17 dB lower than the signal and 3dB higher than the noise Lower noise shows higher Spike rate discharge. In C, all curves get saturated at a higher sound level
  • B and D: a low SR ANF (Shifting with higher sound level) Larger the numbers, the higher the noise level Low SR is responsible for coding
31
Q

What is the impact of background noise in relation to spontaneous rates? (4)

A
  1. Low SR ANFs: highly resistant to noise (in terms of their response to signal)
  2. High SR units, saturated by background noise
  3. Low SR units are critical for signal coding in noise
  4. Low SR units are more sensitive to noise damage
32
Q

How does background noise change the ANF function? (2)

A
  1. By mechanical interaction like two-tone suppression
  2. By efferent control
33
Q

When increasing phase locking, what conclusions can we see about the thresholds?

A

Phase locking occurs before a significant rate increase, so PL has a lower threshold than the rate threshold

34
Q

How does phase locking influence the threshold? (3)

A

In this graph, the threshold of synchronization is lower than the rate threshold

Phase Locking has a lower threshold than the rate threshold because it occurs before the rate change The difference in this graph at the red line is roughly 20 dB

Phase Locking is important for intensity coding

CMSD5280 Audition ll (19 decks)

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