Hair cells located near the base of the basilar membrane respond best to ________ sounds.

The Mechanics of Hearing

Be able to explain what the inner ear comprises (cochlea and vestibular organs).

Know the basilar membrane in inner ear and whether high frequencies are at the base or the apex.

The inner ear includes the cochlea, encased in the temporal bone of the skull, in which the mechanical vibrations of sound are transduced into neural signals that are processed by the brain. The cochlea is a spiral-shaped structure that is filled with fluid.

One of the most important principles of hearing, frequency analysis, is established in the cochlea. In a way, the action of the cochlea can be likened to that of a prism: the many frequencies that make up a complex sound are broken down into their constituent frequencies, with low frequencies creating maximal basilar-membrane vibrations near the apex of the cochlea and high frequencies creating maximal basilar-membrane vibrations nearer the base of the cochlea. This decomposition of sound into its constituent frequencies, and the frequency-to-place mapping, or “tonotopic” representation, is a major organizational principle of the auditory system, and is maintained in the neural representation of sounds all the way from the cochlea to the primary auditory cortex.

Hair cells located near the base of the basilar membrane respond best to ________ sounds.
Fig.5.8.1.  The ear is divided into outer (the pinna and the tympanic membrane), middle (the three ossicles: malleus, incus, and stapes), and the inner ear (Provided by: OpenStax. License: CC-BY 4.0)

The place theory of pitch perception suggests that different portions of the basilar membrane are sensitive to sounds of different frequencies. More specifically, the base of the basilar membrane responds best to high frequencies and the tip of the basilar membrane responds best to low frequencies. Therefore, hair cells that are in the base portion would be labeled as high-pitch receptors, while those in the tip of basilar membrane would be labeled as low-pitch receptors (Shamma, 2001).

References:
Shamma S. On the role of space and time in auditory processing. Trends Cogn Sci. 2001 Aug 1;5(8):340-348. doi: 10.1016/s1364-6613(00)01704-6. PMID: 11477003.

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OpenStax, Psychology Chapter 5.4 Hearing
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Download for free at http://cnx.org/contents/.
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NOBA, Hearing
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License: CC BY-NC-SA 4.0

Learning Objectives

  • Explain how we encode and perceive pitch and localize sound
  • Describe types of hearing loss

Pitch Perception

We know that different frequencies of sound waves are associated with differences in our perception of the pitch of those sounds. Low-frequency sounds are lower pitched, and high-frequency sounds are higher pitched. But how does the auditory system differentiate among various pitches? Several theories have been proposed to account for pitch perception. We’ll discuss two of them here: temporal theory and place theory. The temporal theory of pitch perception asserts that frequency is coded by the activity level of a sensory neuron. This would mean that a given hair cell would fire action potentials related to the frequency of the sound wave. While this is a very intuitive explanation, we detect such a broad range of frequencies (20–20,000 Hz) that the frequency of action potentials fired by hair cells cannot account for the entire range. Because of properties related to sodium channels on the neuronal membrane that are involved in action potentials, there is a point at which a cell cannot fire any faster (Shamma, 2001). The place theory of pitch perception suggests that different portions of the basilar membrane are sensitive to sounds of different frequencies. More specifically, the base of the basilar membrane responds best to high frequencies and the tip of the basilar membrane responds best to low frequencies. Therefore, hair cells that are in the base portion would be labeled as high-pitch receptors, while those in the tip of basilar membrane would be labeled as low-pitch receptors (Shamma, 2001). In reality, both theories explain different aspects of pitch perception. At frequencies up to about 4000 Hz, it is clear that both the rate of action potentials and place contribute to our perception of pitch. However, much higher frequency sounds can only be encoded using place cues (Shamma, 2001).

Sound Localization

The ability to locate sound in our environments is an important part of hearing. Localizing sound could be considered similar to the way that we perceive depth in our visual fields. Like the monocular and binocular cues that provided information about depth, the auditory system uses both monaural (one-eared) and binaural (two-eared) cues to localize sound.

Each pinna interacts with incoming sound waves differently, depending on the sound’s source relative to our bodies. This interaction provides a monaural cue that is helpful in locating sounds that occur above or below and in front or behind us. The sound waves received by your two ears from sounds that come from directly above, below, in front, or behind you would be identical; therefore, monaural cues are essential (Grothe, Pecka, & McAlpine, 2010).

Binaural cues, on the other hand, provide information on the location of a sound along a horizontal axis by relying on differences in patterns of vibration of the eardrum between our two ears. If a sound comes from an off-center location, it creates two types of binaural cues: interaural level differences and interaural timing differences. Interaural level difference refers to the fact that a sound coming from the right side of your body is more intense at your right ear than at your left ear because of the attenuation of the sound wave as it passes through your head. Interaural timing difference refers to the small difference in the time at which a given sound wave arrives at each ear (Figure 1). Certain brain areas monitor these differences to construct where along a horizontal axis a sound originates (Grothe et al., 2010).

Hair cells located near the base of the basilar membrane respond best to ________ sounds.

Figure 1. Localizing sound involves the use of both monaural and binaural cues. (credit “plane”: modification of work by Max Pfandl)

Try It

Hearing Loss

Deafness is the partial or complete inability to hear. Some people are born without hearing, which is known as congenital deafness. Other people suffer from conductive hearing loss, which is due to a problem delivering sound energy to the cochlea. Causes for conductive hearing loss include blockage of the ear canal, a hole in the tympanic membrane, problems with the ossicles, or fluid in the space between the eardrum and cochlea. Another group of people suffer from sensorineural hearing loss, which is the most common form of hearing loss. Sensorineural hearing loss can be caused by many factors, such as aging, head or acoustic trauma, infections and diseases (such as measles or mumps), medications, environmental effects such as noise exposure (noise-induced hearing loss, as shown in Figure 5.20), tumors, and toxins (such as those found in certain solvents and metals).

Hair cells located near the base of the basilar membrane respond best to ________ sounds.

Figure 2. Environmental factors that can lead to sensorineural hearing loss include regular exposure to loud music or construction equipment. (a) Musical performers and (b) construction workers are at risk for this type of hearing loss. (credit a: modification of work by “GillyBerlin_Flickr”/Flickr; credit b: modification of work by Nick Allen)

Given the mechanical nature by which the sound wave stimulus is transmitted from the eardrum through the ossicles to the oval window of the cochlea, some degree of hearing loss is inevitable. With conductive hearing loss, hearing problems are associated with a failure in the vibration of the eardrum and/or movement of the ossicles. These problems are often dealt with through devices like hearing aids that amplify incoming sound waves to make vibration of the eardrum and movement of the ossicles more likely to occur.

When the hearing problem is associated with a failure to transmit neural signals from the cochlea to the brain, it is called sensorineural hearing loss. This type of loss accelerates with age and can be caused by prolonged exposure to loud noises, which causes damage to the hair cells within the cochlea. One disease that results in sensorineural hearing loss is Ménière’s disease. Although not well understood, Ménière’s disease results in a degeneration of inner ear structures that can lead to hearing loss, tinnitus (constant ringing or buzzing), vertigo (a sense of spinning), and an increase in pressure within the inner ear (Semaan & Megerian, 2011). This kind of loss cannot be treated with hearing aids, but some individuals might be candidates for a cochlear implant as a treatment option. Cochlear implants are electronic devices that consist of a microphone, a speech processor, and an electrode array. The device receives incoming sound information and directly stimulates the auditory nerve to transmit information to the brain.

What Do You Think?: Deaf Culture

In the United States and other places around the world, deaf people have their own language, schools, and customs. This is called deaf culture. In the United States, deaf individuals often communicate using American Sign Language (ASL); ASL has no verbal component and is based entirely on visual signs and gestures. The primary mode of communication is signing. One of the values of deaf culture is to continue traditions like using sign language rather than teaching deaf children to try to speak, read lips, or have cochlear implant surgery.

When a child is diagnosed as deaf, parents have difficult decisions to make. Should the child be enrolled in mainstream schools and taught to verbalize and read lips? Or should the child be sent to a school for deaf children to learn ASL and have significant exposure to deaf culture? Do you think there might be differences in the way that parents approach these decisions depending on whether or not they are also deaf?

Try It

Think It Over

If you had to choose to lose either your vision or your hearing, which would you choose and why?

Glossary

binaural cue: two-eared cue to localize sound

cochlear implant: electronic device that consists of a microphone, a speech processor, and an electrode array to directly stimulate the auditory nerve to transmit information to the brain

conductive hearing loss: failure in the vibration of the eardrum and/or movement of the ossicles

congenital deafness: deafness from birth

deafness: partial or complete inability to hear

interaural level difference: sound coming from one side of the body is more intense at the closest ear because of the attenuation of the sound wave as it passes through the head

interaural timing difference: small difference in the time at which a given sound wave arrives at each ear

Ménière’s disease: results in a degeneration of inner ear structures that can lead to hearing loss, tinnitus, vertigo, and an increase in pressure within the inner ear

monaural cue: one-eared cue to localize sound

place theory of pitch perception: different portions of the basilar membrane are sensitive to sounds of different frequencies

sensorineural hearing loss: failure to transmit neural signals from the cochlea to the brain

temporal theory of pitch perception: sound’s frequency is coded by the activity level of a sensory neuron

vertigo: spinning sensation

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How does the basilar membrane respond to a sound wave?

The basilar membrane vibrates in different regions, according to the frequency of the sound waves impinging on it. Likewise, the hair cells that lay above it are most sensitive to a specific frequency of sound waves.

What frequency does the basilar membrane respond to?

The stimulus frequency evoking a maximal response at the basilar membrane varied from 140 to 496 Hz, with an average of 253 ± 12 Hz (Fig. 1E), whereas the average best frequency at the Hensen cells was 199 ± 9 Hz (range: 140–350 Hz).

Where does sound go after basilar membrane?

The sound vibrations cause fluid inside the cochlea to ripple, and a traveling wave forms along the basilar membrane. The wave causes the cilia to move up and down. Cilia near the base of the cochlea detect higher-pitched frequencies, such as a cell phone ringing.

Which part of the basilar membrane responds to low frequency sound waves?

It is known from experiments that different sounds produce different responses of the basilar membrane. Sounds with low frequency produce resonant peak near the apex and sounds with high frequency near the stapes.