Deck 11: Hearing

Question 1

We saw that decibels are used to compress the large range of sound pressures in the environment into more manageable numbers. Describe how this same principle is used in the Richter scale to compress ranges of earth vibrations from barely perceptible tremors to major earthquakes into a smaller range of numbers.

Answer 1

The Richter scale is also called as Richter magnitude scale; it is a device that is used to assign particular magnitude to quantify energy that is released via an earthquake. It was developed in 1930s, and is a logarithmic scale having base 10.
It defines the magnitude in the form of logarithm in ratio of amplitude of the seismic wave towards an arbitrary. When measured with a seismometer, if an earthquake measures 5.0 on a Richter scale, shows shaking amplitude. It is 10 times higher than the earthquake that is registered as 4.0. It releases energy that is 31.6 times released by a lesser earthquake.
The principle can be expressed by the given formula. Where, A is maximum excursion of seismograph, A 0 depends on the epicentral distance of station.
The magnitude is expressed in terms of decimal fractions and whole numbers. Logarithmic basis of the scale raises each whole number and it represents tenfold increase in the measured amplitude.

Question 2

Presbycusis usually begins with loss of high-frequency hearing and gradually involves lower frequencies. From what you know about cochlear function, can you explain why the high frequencies are more vulnerable to damage?
Figure Hearing loss in presbycusis as a function of age. All of the curves are plotted relative to the 20-year-old curve, which is taken as the standard.

Answer 2

Cochlea, a part of the inner ear comprises of the sensory organ for hearing. The sound travels in the auditory canal across the tympanic membrane, which connects the receptors of the inner ear and sends impulses to the brain.
The cochlea is a bony structure containing endolymph and perilymph fluid. The organs of corti are the sensory receptors present inside the cochlea. It helps in the holding of the hair cells, which are the nerve receptors for hearing.
The middle ear bones create a mechanical energy that pushes the membrane in cochlea and cause the fluid of cochlea to move. This fluid stimulates the hair cells to send signals. The brain receives the nerve impulses through the auditory nerve, which delivers the impulses to the cochlear nucleus. Then these nerve impulses are carried to the hearing part of the brain.
The higher frequencies leads to losing hearing sensitivity because, the cochlea is arranged tonotopically from base to apex along with the hair cells. The higher frequency leads to more wear and tear of these hair cells as compared to the lower frequencies.

Question 3

What are some of the functions of sound? Especially note what information sound provides that is not provided by vision.

Answer 3

Sound can be defined on the basis of both physical as well as perpetual response. The physical definition states that pressure changes in the air is responsible for the production of sound whereas according to perpetual definition, sound refers to the experience produced in response hearing process.
Some important functions of sounds are as follows:
1. It is the major form communication. The person can understand the communication by ears.
2. Sound waves are used as the signaling systems in trains and cars as sounds are used in horns or sirens.
3. Sound waves are used for the detection of depth of the rivers and to estimate the distance between the far away objects.
4. The process of sonication is used in the disruption of bacterial colonies.
5. In tissue culture, sonication is used for the cell growth and development.
Lack in visual ability leads to isolation from materialistic world but lack in hearing ability leads to the isolation from the people. Sound is responsible for seeking attention. Without sound people will not be able to draw others attention.

Question 4

What are two possible definitions of sound? (Remember the tree falling in the forest.)

Question 5

How is the sound stimulus described in terms of pressure changes in the air? What is a pure tone? sound frequency?

Question 6

What is the amplitude of a sound? Why was the decibel scale developed to measure amplitude? Is decibel "perceptual" or "physical"?

Question 7

What is the relationship between sound level and loudness? Which one is physical, and which one is perceptual?

Question 8

What is the audibility curve, and what does it tell us about the relationship between a tone's physical characteristics (level and frequency) and perceptual characteristics (threshold and loudness)?

Question 9

What are tone height and tone chroma?

Question 10

What is timbre? Describe the characteristics of complex tones and how these characteristics determine timbre.

Question 11

Describe the structure of the ear, focusing on the role that each component plays in transmitting the vibrations that enter the outer ear to the auditory receptors in the inner ear.

Question 12

Focusing on the inner ear, describe (a) what causes the bending of the cilia of the hair cells; (b) what happens when the cilia bend; (c) why we say that the electrical signal follows the timing of the sound stimulus.

Question 13

Describe Békésy's discovery of how the basilar membrane vibrates. Specifically, what is the relationship between sound frequency and basilar membrane vibration?

Question 14

What is a cochlear implant? Why do we say that it is a practical application that can be traced to discoveries of basic research?

Question 15

How do measurements of basilar membrane vibration made by modern researchers compare to Békésy's measurements? What is the reason for the difference? How can the difference be explained by the cochlear amplifier?

Question 16

How does the basilar membrane vibrate to complex tones?

Question 17

Up to this point, how does what we have described about the functioning of the ear apply to the perceptual process? Why can't we say, based on what we have covered so far, that we understand how we perceive sound?

Question 18

Considering what we know about (a) how information about sound frequency is represented in the ear and (b) the relation between frequency, repetition rate, and perception, what can we conclude about the relation between the physiology of the ear and pitch perception? Be sure you consider the roles of both place and timing information.

Question 19

What is the tonotopic map in the brain?

Question 20

Describe the experiment that suggests a relationship between firing of neurons in the auditory cortex and the pitch of complex tones.

Question 21

What is the connection between hair cell damage and hearing loss? exposure to occupational or leisure noise and hearing loss?

Question 22

Describe the procedures for measuring auditory thresholds in infants. How does the infant's audibility curve compare to the adult curve?

Question 23

Describe experiments that show that newborn infants can recognize their mother's voice, and that this capacity can be traced to the infants' having heard the mother talking during development in the womb.