BBB - Hearing Lesson

Learning Targets:

  • Explain the properties of air pressure waves that we perceive as sound.
  • Describe the process by which the ear converts sound energy into neural signals.
  • Discuss the mechanisms involved in detecting loudness, distinguishing pitch, and determining the location of sounds.

Courtesy of the AP psychology course and exam description, effective fall 2024. (n.d.). Links to an external site.

 

Hearing

Hearing (audition) is the ability to perceive subtle differences in sound (air in motion). It is an important survival instinct, and it is essential for social interactions and language development. Sound waves are what produce our sensory experience of sound. Frequency is the number of wavelengths that pass through a point at a given time. It is usually measured in hertz and determines a tone's pitch or experienced highness or lowness. Most sound waves are of several wave frequencies. Amplitude is how loud the sound is. The higher the wave, the louder the sound. This is measured in decibels. The absolute threshold for hearing is zero decibels.

The Anatomy of the Ear: Elastic cartilages Auditory ossicles Semicircular canals Vestibule -Vestibulocochlear nerve -Cochlea Auricle Round window Auditory tube Oval window Tympanic cavity External acoustic meatus Tympanic membrane

 

Our ear is composed of an outer, middle, and inner ear. Sound waves are collected in the outer ear and transduced into a neural message in the middle and inner ear. Take a moment to examine the anatomy of the ear and the process of transduction.

Infographic representing Sound waves and the ear. Full text available below image.

Sound Waves and the Ear:

  1. Sound wave represents alternating areas of high and low pressure.
  2. Tympanic membrane vibrates in response to sound wave.
  3. Vibrations are amplified across ossicles.
  4. Vibrations against oval window set up standing wave in fluid of vestibuli.
  5. Pressure bends the membrane of the cochlear duct at a point of maximum vibration for a given frequency, causing hair cells in the basilar membrane to vibrate.

 

Choose each of the items below to learn more about Transduction in the Ear.

     1. Sound Waves Collected     
        

Sound waves are collected in the outer ear by the pinna.

    
     2. Amplification     
        

Sound waves are amplified in the middle ear once they bounce into the eardrum. The vibrations from the eardrum are amplified by three tiny bones: the hammer, the anvil, and the stirrup. 

    
     3. Passage through the oval window     
        

The oval window is a membrane that separates the middle ear from the inner ear. Its vibrations are relayed to the cochlea.

    
     4. Inside the cochlea     
        

The cochlea is a fluid filled tube that ripples creating a vibration that is transmitted to the basilar membrane.

    
     5. Inside the basilar membrane     
        

Inside the basilar membrane – Inside the basilar membrane there are sensory receptors for sound called hair cells or cilia. When they vibrate they create an neural impulse called organ of Corti. These neural impulses leave the ear traveling to the thalamus and then the auditory nerve.

    

 

 

Please take a moment to view the following video on Auditory Structure.

 

Perceiving Loudness, Pitch, and Location

High and low pitched sounds are determined by the frequency of a sound wave. The basilar membrane is a key component in our ability to hear pitch. There are two theories that describe its role in determining sound.

Place Theory

This theory states that we hear different pitches because sound waves trigger different hairs to vibrate at various places along the basilar membrane. High-frequency sounds have a maximum vibration near the stirrup end of the basilar membrane, while low-frequency sounds have the opposite effect. This theory accounts for both high and low-frequency sounds.

Volley Theory

The Volley Theory offers an interesting perspective. This theory suggests that our brains interpret pitch based on the firing rate of groups of auditory neurons, rather than the individual firing rate of a single neuron. According to the Volley Theory, when different groups of neurons fire in a coordinated manner, they create the sensation of pitch in our minds. This concept sheds light on how our brains process and make sense of the complex auditory signals that we encounter every day.

Frequency Theory

The frequency theory states that the basilar membrane vibrates the incoming sound waves by triggering neural impulses at the same rate as the sound wave. It explains how we hear low-pitched sounds. A sound wave of 100 hertz causes vibrations 100 times per second. One problem with this theory is that neurons cannot fire more than 1000x per second, but some wave frequencies are above 1000 waves per second.

Cochlear Implant: Sound processor Internal implant Hearing nerve Cochlea Electrode

Deafness

When someone is deaf or partially deaf, they experience a lack of hearing. Two theories are proposed to explain different types of deafness.

  1. Conduction Deafness or Conduction Hearing Loss is when the eardrum is punctured, or something goes wrong causing the tiny bones in the middle ear to lose the ability to vibrate. When this happens, it is difficult to hear any tones. To counter this effect hearing aids can be used. They produce amplified vibrations.
  2. Nerve Deafness or Sensorineural Hearing Loss is caused by disease, age, or overexposure to loud sounds (85 decibels or above). In this type of deafness, the hair cells in the cochlea become damaged or destroyed. Once damaged they remain dead. However, a cochlear implant can be surgically placed to bypass the damaged portion of the ear and directly stimulate the auditory nerve.

 

 Please take a moment to view the following video on Cochlear Implants.

 

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