UNIT 3: Sensation and Perception
Learning Targets
24-1 Describe the characteristics of air pressure waves that we hear as sound.
24-2 Explain how the ear transforms sound energy into neural messages.
24-3 Discuss how we detect loudness, discriminate pitch, and locate sounds.
What is audition?
the sense or act of hearing
How do air pressure waves �become sound?
Draw a bow across a violin, and you will unleash the energy of sound waves.
Air molecules, each bumping into the next, create waves of compressed and expanded air, like the ripples on a pond circling out from a tossed stone.
As we swim in our ocean of moving air molecules,
our ears detect these brief air pressure changes.
What are characteristics of �sound waves?
frequency (wavelength)
amplitude (height)
What information do sound waves �give us?
What pitch am I hearing?
How loud is the sound I am hearing?
Would you expect long or short �wavelengths…
1
…when a soprano sings an aria?
2
…when a baritone sings along?
AP® Exam Tip 1
Note that both light and sound travel in waves.
In each case, the amplitude and length of the waves
are important to learn for the AP® exam.
What are the three divisions of the ear?
The ear is divided into outer, middle and inner sections.
How does the ear transform sound �into neural messages?
Passing through accessory structures to sense receptors, vibrating air triggers nerve impulses that the
brain decodes as sounds.
What is the auditory canal?
the channel located in the outer ear that funnels sound waves from the pinna to the tympanic membrane
(ear drum)
What is the ear drum (tympanic membrane)?
The ear drum, or the tympanic membrane, is a thin layer of tissue that vibrates in response to sound waves.
What are the ossicles?
The ossicles, made up of the three smallest bones in the human body, the incus, the malleus and the stapes, transfer the sound wave vibrations from the tympanic membrane to the oval window of the cochlea.
What is the oval window?
The oval window is the membrane-covered opening of the cochlea. It vibrates when it receives the sound waves and causes the fluid inside the cochlea to move.
What is the cochlea?
The cochlea is a coiled, bony, fluid-filled tube in the inner ear.
Sound waves traveling through the cochlear
fluid trigger
nerve impulses.
Can you trace the path of sound �through the ear so far?
Use the terms you just learned to label each structure.
1. What Would You Answer?
When you listen to music, the sound waves cause your ____ to vibrate first.
B. hammer, anvil, and stirrup (malleus, incus and stapes)
C. eardrum (tympanic membrane)
D. oval window
AP® Exam Tip 2
You may notice that some sensory structures are referred to in more than one way. The Latin designation is important to know:
tympanic membrane
Your textbook author has simplified the terms and uses the popular name for the structure:
eardrum
Learn both names and understand they refer to the same structure(s) so you won’t be confused on the AP® exam.
How does the sound wave move �through the inner ear?
Accessory structures move the sound wave to the sense receptors(stereocilia) in the inner ear where the wave energy undergoes transduction to neural energy that the brain can interpret.
How does transduction �occur in the inner ear?
The motion of the sound vibration against the oval window of the cochlea causes ripples in the basilar membrane,
bending the hair cells lining its surface,
AP® Exam Tip 3
Although the basilar membrane is not considered a key term in your text, it is considered a key term on the AP® exam.
Free-Response Questions (FRQs) and multiple- choice questions frequently ask about the basilar membrane.
Make sure to learn about the way sound waves are transduced into neural impulses via the cilia on the basilar membrane.
How does the nerve impulse �move out of the ear?
The hair cell (cilia) movements in turn trigger impulses in adjacent nerve cells, whose axons
converge to form the auditory nerve.
How does the message carry to the brain?
The auditory nerve carries the neural messages to your
thalamus and then on to the auditory cortex in
your brain’s temporal lobes.
Trace the path of sound through the ear.
Put it all together and label the process.
AP® Exam Tip 4
Pay attention to how many pages are devoted
to each of the senses.
Not only does this represent the complexity of the sensory system, it also represents how likely you are to find questions about that system on the AP® exam.
Given that more pages are devoted to vision than hearing, there are likely to be more exam questions on vision.
What are two types of hearing loss?
sensorineural
Damage to the cochlea’s hair cell receptors or the auditory nerve can cause
sensorineural hearing loss.
With auditory nerve damage, people
may hear sound but have trouble discerning what someone is saying.
conduction
Damage to the mechanical system—the eardrum and middle ear bones—that conducts sound waves to the cochlea can cause conduction hearing loss. It is less common than sensorineural hearing loss.
How much sound is too much sound?
As a general rule, any noise we cannot talk over (loud machinery, fans screaming
at a sports event, music blasting at maximum volume) may be harmful, especially if prolonged
and repeated.
(Roesser, 1998)
What is the problem with headphones?
Headphones direct all of the sound waves into the auditory canal and bombard the basilar membrane.
In the open air, sound waves disperse and are not all directed to one location.
How can headphones help?
When
Super Bowl-winning quarterback Drew
Brees celebrated New Orleans’ 2010
victory amid pandemonium, he used ear muffs to protect the vulnerable hair cells of his son, Baylen.
What is the research on hearing loss?
Since the early 1990s, teen hearing loss has risen by a third and now affects 1 in 5 teens.
(Shargorodsky et al., 2010)
After three hours of a rock concert averaging 99
decibels, 54 percent of teens reported not hearing as well, and 1 in 4 had ringing in their ears.
Teen boys more than teen girls or adults blast themselves with loud volumes for long periods.
(Zogby, 2006)
What is a cochlear implant?
a device for
converting sounds into electrical
signals and stimulating the
auditory nerve through electrodes
threaded into the cochlea
How does a cochlear implant work?
Cochlear implants work by translating
sounds into electrical signals that are
transmitted to the cochlea and, via the
auditory nerve, relayed to the brain.
2. What Would You Answer?
Because of the repeated exposure to loud noise they experience during their daily jobs, airport ground workers are most susceptible to damage which of the following?
B. cochlea
C. ganglion cells
D. bipolar cells
How does the brain detect loudness?
A soft, tone activates only the few hair cells attuned to its frequency.
Given louder sounds, neighboring hair cells also respond.
Thus, the brain interprets loudness from the number of activated hair cells.
What is one theory of how the �brain detects pitch?
Place theory presumes that we hear different pitches because different sound waves
trigger activity at different spots along the cochlea’s basilar membrane.
Thus, the brain determines a sound’s pitch by recognizing the specific area (on the membrane) that is generating the neural signal.
What is the frequency theory?
Frequency theory (also called temporal theory) suggests an alternative:
the brain reads pitch by monitoring the frequency of neural impulses traveling up the auditory nerve.
The whole basilar membrane vibrates with the incoming sound wave, triggering neural impulses to the brain at the same rate as the sound wave.
If the sound wave has a frequency of 100 waves per second, then 100 pulses per second
travel up the auditory nerve.
How does the volley principle explain �hearing higher frequency sounds?
By firing in rapid succession, neurons can achieve a combined frequency above 1000 waves per second
Like soldiers who alternate firing so that some can shoot while others reload, achieving greater combined fire power, neural cells
can alternate firing.
How do the two theories work together to explain how we hear pitch?
Place theory best explains how we sense
high pitches.
Frequency theory, extended by the volley principle, also explains how we sense low pitches.
Finally, some combination of place
and frequency theories likely explains how we sense pitches in the intermediate range.
3. What Would You Answer?
Which of the following reflects the notion that pitch is related to the stimulation of different areas of the cochlea’s basilar membrane?
B. frequency theory
C. volley principle
D. sound localization
How do we locate sounds?
Sound waves strike one ear sooner and more intensely than
the other. From this information, our nimble brain can compute the sound’s location.
Learning Target 24-1 Review
Describe the characteristics of air
pressure waves that we hear as sound.
Learning Target 24-2 Review
Explain how the ear transforms sound
energy into neural messages.
Learning Target 24-2 Review cont.
Explain how the ear transforms sound
energy into neural messages.
Learning Target 24-3 Review
Discuss how we detect loudness,
discriminate pitch, and locate sounds.
Learning Target 24-3 Review cont.
Discuss how we detect loudness,
discriminate pitch, and locate sounds.