Chapter 11 - Hearing Flashcards
1- Physical and Perceptual
Aspects of Sound
Two definitions of “sound”
* Physical definition: pressure changes in the air or other medium
* Perceptual definition: the experience we have
when we hear.
Loud speakers produce sound through a process.
* The diaphragm of the speaker moves out,
pushing air molecules together called
condensation (increase in pressure)
* The diaphragm also moves in, pulling the air molecules apart called rarefaction (decrease in pressure).
* The cycle of this process creates alternating
high- and low-pressure regions that travel
through the air.
2- Pure tones
Pure Tones
Pure tone: created by a sine wave
- Amplitude: difference in pressure between high and
low peaks of wave - Perception of amplitude is known as loudness.
- Decibel (dB) is used as the measure of loudness.
- Number of dB = 20 logarithm(p/po).
- The decibel scale relates the amplitude of the stimulus with the psychological experience of loudness.
High amplitude perceived as loud, low amplitude perceived as soft
Frequency: number of cycles within a given time period
* Measured in Hertz (Hz): 1 Hz is one cycle per second.
* Perception of pitch is related to frequency.
* Tone height is the increase in pitch that happens
when frequency is increased.
High frequency perceived as high pitch, low frequency perceived as low pitch
3- Complex Tones and Frequency Spectra
Complex Tones and Frequency Spectra
* Both pure and some complex tones are periodic tones.
* Fundamental frequency
-The repetition rate and is called the first harmonic.
* Periodic complex tones
- consist of several pure tones called harmonics.
* Additional harmonics
- multiples of the fundamental frequency.
* Additive synthesis
- process of adding harmonics to create complex
sounds
* Frequency spectrum
- display of harmonics of a complex sound
Relative amplitude and decibels for environmental sounds (see graph)
4- Perceptual aspects of sound: Loudness and pitch
Loudness is the perceptual quality most closely related to the level or amplitude of
an auditory stimulus.
Amplitude in dB (decibels)
- Human hearing range: 20 to 20,000 Hz
- Audibility curve: shows the threshold of hearing in relation to frequency
- Changes on this curve show that humans are most sensitive to 2,000 to 4,000 Hz.
- Auditory response area: falls between the audibility curve and the threshold for
feeling. - It shows the range of response for human audition.
*Equal loudness curves: determined by using a
standard 1,000 Hz tone
* Two dB levels are used: 40 and 80
* Participants match the perceived loudness of all
other tones to the 1,000 Hz standard.
* Resulting curves show that tones sound:
- At almost equal loudness at 80 dB.
- Softer at 40 dB for high and low frequencies than the rest of the tones in the range.
(??? idgi, read textbook or video)
Pitch – the perceptual quality we describe as high
and low
Timbre: all other perceptual aspects of a sound
besides loudness, pitch, and duration
different perception with the same wavelengths. what makes different instruments sound different despite same frequency.
* It is closely related to the harmonics, attack, and decay of a tone.
Effect of missing fundamental frequency:
* Removal of the first harmonic results in a
sound with the same perceived pitch, but
with a different timbre.
* This is called periodicity pitch.
-Attack of tones: buildup of sound at the beginning
of a tone
-Decay of tones: decrease in sound at end of tone
On a piano
Frequency increases from left of piano to right
As frequency increases, tone height increases
Same tone chroma= ex: all the A notes on the piano
5- From Pressure Changes to
Electricity
Outer ear: pinna and auditory canal
* Pinna helps with sound location.
* Auditory canal: tube-like 3 cm long structure
- Protects the tympanic membrane at the end of the
canal.
- The resonant frequency of the canal amplifies
frequencies between 1,000 and 5,000 Hz.
Middle ear
* Two cubic centimeter cavity separating inner from outer
ear
* Contains the three ossicles
- Malleus: moves due to the vibration of the tympanic
membrane (ear drum)
- Incus: transmits vibrations of malleus
- Stapes: transmits vibrations of incus to the inner ear
via the oval window of the cochlea
Functioning of ossicles:
* Outer and inner ear are filled with air.
* Inner ear is filled with fluid that is much denser
than air.
* Pressure changes in air transmit poorly into the denser medium.
* Ossicles act to amplify the vibration for better
transmission to the fluid.
* Middle ear muscles dampen the ossicles’ vibrations to
protect the inner ear from potentially damaging
stimuli.
(SEE IMAGES)
Inner ear (I think)
*Key structures
- Basilar membrane vibrates in response to sound
and supports the organ of Corti.
- Inner and outer hair cells are the receptors for
hearing.
- Tectorial membrane extends over the hair cells.
*Transduction takes place through this process:
- Cilia bend in response to movement of the
organ of Corti and the tectorial membrane.
- Movement in one direction opens ion channels.
- Movement in the other direction closes the
channels.
- This causes bursts of electrical signals.
How the Basilar Membrane Vibrates
Békésy’s Place Theory of Hearing
* Frequency of sound is indicated by the place on the organ of Corti that has the
highest firing rate
Functions as a Filter
*Tonotopic map
- Cochlea shows an orderly map of frequencies along its
length.
- Apex responds best to low frequencies.
- Base responds best to high frequencies.
*Neural frequency tuning curves
- Pure tones are used to determine the threshold for
specific frequencies measured at single neurons.
- Plotting thresholds for frequencies results in tuning
curves.
- Frequency to which the neuron is most sensitive is the characteristic frequency.
6- The Physiology of
Pitch Perception
Place theory: based on the relation between a sound’s
frequency and the place along the basilar membrane that is activated.
*Phase locking
- Nerve fibers fire in bursts.
- Firing bursts happen at or near the peak of the sine-wave stimulus.
- Thus, they are “locked in phase” with the wave.
- Groups of fibers fire with periods of silent intervals
creating a pattern of firing.
(idgi, see book and vids)
Temporal coding-major mechanism of pitch perception
Resolved harmonics
Unresolved harmonics
(??)
Outer hair cells destroyed (see graph and book)
7- The Pathway to the Brain
Left ear
Auditory nerve
Cochlear nucleus
(some cross over to right hemisphere, some stay to left hemisphere)
SONIC MG
* SON = superior olivary nucleus
* IC = inferior colliculus
* MG = medial geniculate nucleus
Primary auditory cortex
Core area
Belt area
Parabelt area
(???)
8- Pitch and the brain
See images and read book/watch lecture
9- Hearing Loss
Presbycusis:
* Greatest loss at high frequencies.
* Affects males more severely than females.
* Appears to be caused by exposure to damaging noises or drugs.
Noise-induced hearing loss
* Loud noise can severely damage the organ of Corti.
* Leisure noise can also cause hearing loss.
See images
10- Cochlear Implants
Cochlear Implants
Electrodes are inserted into the cochlea to electrically stimulate auditory nerve fibers.
The device is made up of:
* A microphone worn behind the ear
* A sound processor
* A transmitter mounted on the mastoid bone
* A receiver surgically mounted on the mastoid bone
