Sound is a pressure wave

Figure by MIT OCW. After figure 11.1 in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins, 2001. ISBN: 0683305964.

Speed of sound-1000 ft/sec

- 770 mi/hr

Figure by MIT OCW. After figure 11.3 in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins, 2001.ISBN: 0683305964.

The middle ear

Figure by MIT OCW. After figure 11.5 in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins, 2001.ISBN: 0683305964.

Impedance matching

• Fluid in cochlea has higher impedancethan air : reflection could be a problem.

• Pressure at the cochlea is amplifiedrelative to pressure at the eardrum

• Force = pressure x area

• Work = force x distance

The cochlea is a Fourieranalyzer

• Input– Pressure

• Output– Auditory nerve fibers– Each fibers is selective for sounds of a

characteristic frequency

Pure tones

Figure by MIT OCW. After figure 11.2 in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins, 2001.ISBN: 0683305964.

Frequency tuning

analogous to visual receptive field ,with frequency playing the role of spaceFigure by MIT OCW. After figure 11.19 in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins, 2001.ISBN: 0683305964.

Fourier analysis and synthesis

• Any signal can be written as a sum of sinewaves.

• Any sound is a combination of pure tones.

Power spectrum

• Graph of power versus frequency.

Spectrogram

• Power spectrum as a function of time.

• Power versus frequency and time.

Critical bands through masking

• Detection of pure tone depends on bandwidth of masking noise only if it is narrower than a critical value

• The critical value corresonds roughly to the width of frequency tuning of auditory nerve fibers

Three scale of the cochlea

Figure by MIT OCW. After figure 11.7 in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins, 2001.ISBN: 0683305964.

Basilar membrane

Images removed due to copyright reasons. Please see figure 11.8 in: Bear, Mark F., Barry W.Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.:Lippincott Williams & Wilkins, 2001. ISBN: 0683305964.

Structural gradient

• Base is 100 times stiffer than apex.

• Frequency and amplitude of a traveling wave vary along the basilar membrane.

Figure by MIT OCW. After figure 11.9 in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins, 2001.ISBN: 0683305964.

Place code for frequency

Figure by MIT OCW. After figure 11.10 in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins, 2001.ISBN: 0683305964.

Hair cells and stereocilia

Images removed due to copyright reasons. Please see figures 11.11 a and b in: Bear, Mark F.,Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore,Md.: Lippincott Williams & Wilkins, 2001. ISBN: 0683305964.

The organ of Corti

• Inner hair cells– Single row of 3500– Tip end below tectorial

membrance• Outer hair cells

– Three rows of 5000– Tip attached to tectorial

membrance• Synapse onto spiral ga

nglion cells.

Figure by MIT OCW. After figure 12.11in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins, 2001.ISBN: 0683305964.