The auditory nerve response

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The auditory nerve response
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The bottom line

• Each auditory nerve fiber responds to a narrow
  band of frequencies, with a phase locked response
  that increases in rate with sound intensity.

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A tuning curve shows

1. the response of a device to a fixed amplitude
   input at different frequencies
2. the amplitude of the input at each frequency
   required to produced an equal response in a
   device.

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Auditory nerve tuning curves
From Kiang et al. (1965)
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The auditory nerve contains an array of tuned
fibers
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Characteristics of auditory nerve tuning curves

• Band-pass in shape, about 1/3 octave wide.
• Best or characteristic frequency (CF).
• Steep high-frequency slope
• Extended low- frequency tail

From Kiang et al. (1965)
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Characteristics of the AN tuning curve reflect
properties of the traveling wave envelope
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Characteristics of the AN tuning curve reflect
properties of the traveling wave envelope
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Differences between high- and low-frequency
tuning curves
From Kiang et al. (1965)
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Auditory nerve tuning curves have steep
high-frequency slopes because the traveling wave
envelope

1. builds up from the base of the cochlea
2. reaches a peak at a place that depends on the
   frequency
3. drops in amplitude rapidly once the peak
   response is reached

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Auditory nerve tuning curves have extended
low-frequency tails because the traveling wave
envelope

1. builds up from the base of the cochlea
2. reaches a peak at a place that depends on the
   frequency
3. drops in amplitude rapidly once the peak
   response is reached

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Auditory nerve tuning curves have sharp tips
because the traveling wave envelope

1. builds up from the base of the cochlea
2. reaches a peak at a place that depends on the
   frequency
3. drops in amplitude rapidly once the peak
   response is reached

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Input-output functions
Number of action potentials per second
Intensity
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When no sound is presented to the ear, hair cell
transduction channels

1. are closed.
2. are open.
3. are closed most of the time, but pop open
   sometimes.
4. are open most of the time, but slam shut
   sometimes.

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Spontaneous activity and response saturation
From Moore (1997)
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Response saturation is

1. the tendency to stop responding at high
   intensities.
2. the tendency to increase responding
   exponentially at high intensities.
3. the tendency for responding to remain constant
   at high intensities.

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Phase locking
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Phase locking
From Yost (1994)
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Period Histograms of Complex Sounds
From Brugge et al. 1969
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Amplitude modulated (AM) tone
Fine structure v. envelope of waveform
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Response histogram in auditory nerve fiber for AM
tone
From Joris et al. (2004)
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Phase locking

1. indicates when there are positive peaks in sound
   pressure
2. indicates when there are negative peaks in sound
   pressure
3. traces out the positive parts of the time
   waveform of sound
4. represents the phase spectrum of a sound

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Phase locking and intensity coding
High intensity
Low intensity
High frequency
Same intensity
Low frequency
Same frequency
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Does the auditory nerve response remain the same
over time?
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Constructing a poststimulus time histogram
Etc.
Etc.
Etc.
Etc.
Time (ms)
spikes
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2
3
3
1
1
2
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PST histogram of auditory nerve fiber for
unmodulated tone
Onset response
Adaptation
Recovery
From Gelfand (1998)
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Envelope of sound v. envelope of auditory nerve
response
Number of action potentials
Amplitude
Time
Time
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Adaptation is

1. the decrease in a neurons response rate with
   continued stimulation
2. the cessation of a neurons response with
   continued stimulation
3. the continuation of a neurons response after
   stimulation stops
4. the increase in a neurons response over time

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Conclusions

• Each auditory nerve fiber responds to sound over
  about a ?-octave range.
• An auditory nerve fiber increases its firing rate
  when the intensity of sound increases, but the
  response saturates.
• Auditory nerve fibers produce action potentials
  that follow the fine structure and envelope of
  sound, but adaptation interferes with envelope
  coding.