PSYCH 1XX3 Lecture Notes - Lecture 14: Stirrup, Olivary Body, Hair Cell
Audition
The Auditory Mechanisms of Different Species
Sound Frequencies
- Species vary in the range of frequencies they can detect
o Ex. Dogs can hear higher frequency soundwaves
- Sound frequency perception varies across vertebrates
o Humans can perceive sound between 20 and 20,000 Hz
Environmental Impacts on Auditory Structure
- The structure determines the range of frequency perception
- The Basilar Membrane contains the hearing receptors; sounds
of different frequencies are processed along different areas of the
basilar membrane
o Basilar membrane varies in length across species. Shortest = Amphibians.
Longer = birds. Longest = Mammals
o Basilar membrane encodes different frequencies along its length, so longer membranes = more
frequencies you can hear
The Stimulus – Sound Waves
Sound waves
- The travel in waves, like light, but they travel much slower and require some medium to travel
through
- Sound waves are made by vibrating objects (vocal cords), a sudden burst of air clapping), or by forcing
air past a small cavity (pipe organ).
Changes in Air Pressure
- Air molecules surrounding the source of the sound move, cause a
chain reaction of moving particles.
- These molecules interact with the eardrum. A band of
compressed air cause the eardrum (tympanic membrane) to get
pushed slightly inwards, whereas a band a less dense air particle
causes the eardrum to move outwards.
- Sine Waves
o Pressure changes in sound waves can be a graphed as a sine wave
o The Frequency, Amplitude, and Purity of the wave effects the
sound
▪ Amplitude (Loudness): Greater amplitude correspond to
louder sounds. Measures in a logarithmic scale of decibels
(dB). The perceived loudness of a sound doubles for every
10 dB increase
▪ Frequency (Pitch): Pitch is measures in Hertz (Hz), which represents the number of
cycles per second. High frequency means high pitched sound. Low frequency means low
pitched.
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▪ Purity (Timbre): refers to the complexity of a sound. Two sounds can sound different
even if they play the same note because of the overtones it creates.
The Ear
Structure of the Ear
- Can be divided into three sections: the external, middle,
and inner ear, and each area conducts sounds in a
different way
- Changes in air pressure are channeled through the
external ear, onto the middle ear, and amplified so that it
can be detected as changes in fluid pressure by the inner
ear. These changes in fluid pressure are converted into
neural impulses.
External Ear
- Collects and amplifies sound waves
- Made up of the pinna, ear canal, and eardrum
o Pinna: collects sound waves and direct them along the ear canal. As the ear canal narrows, it
amplifies the sound
o Ear drum: thin membrane that vibrates at the frequency if the incoming sound
Middle Ear
- Begins on the other side of the ear drum, which connects
the ossicles, the three smallest bones in your body. Consist
of the hammer (malleus), anvil (incus), and stirrup (stapes).
- Vibrating ossicles further amplify the sound stimulus. The
ossicles create a lever system beside the oval window to
amplify even more.
Inner Ear
- The oval window connects to the cochlea, in the inner ear. The cochlea is a fluid-filled-tube, 35 mm
long, coiled like a snail shell. It contains the neural tissue that is necessary to transfer the changes in
fluid to neural impulses of audition.
- The oval window is a small opening in the side of the cochlea that displaces the fluid inside the cochlea
when it vibrates
- Inside the cochlea is the basilar membrane, that runs the length of the cochlea like a carpet.
o When oval window is pushed inwards – the waves in the fluid
pushed the basilar membrane downwards
o When the oval window is pushed outwards – the fluid forces
the basilar membrane upwards.
Basilar Membrane
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find more resources at oneclass.com
Document Summary
Species vary in the range of frequencies they can detect: ex. Sound frequency perception varies across vertebrates: humans can perceive sound between 20 and 20,000 hz. The structure determines the range of frequency perception. The basilar membrane contains the hearing receptors; sounds of different frequencies are processed along different areas of the basilar membrane: basilar membrane varies in length across species. Longest = mammals: basilar membrane encodes different frequencies along its length, so longer membranes = more frequencies you can hear. The travel in waves, like light, but they travel much slower and require some medium to travel through. Sound waves are made by vibrating objects (vocal cords), a sudden burst of air clapping), or by forcing air past a small cavity (pipe organ). Air molecules surrounding the source of the sound move, cause a chain reaction of moving particles.
