Module 1

Module 1—The Nervous System

Hearing Pitch and Loudness

 

Read

 

 

You have likely been to a concert or listened to a MP3 player, or perhaps you play a musical instrument. If so, you are familiar with high-pitch (high frequency) and low-pitch (low frequency) sounds. However, do you know how or why you are able to hear high- or low-pitch sounds? How are you able to distinguish between yelling and whispering, or loudness?

 

To understand how people hear, read from “Frequencies of Sound” on page 421 through “The Perception of Sound” on page 424 in the textbook. When you have finished, make summary notes, a concept map, or a flow chart for your course folder.

 

Try This

 

To assure your understanding of the concepts of pitch and loudness, answer the following questions in full sentences. If you are unsure of any of the concepts, consult with your teacher. File your exercise in your course folder.

 

TR 2. Define frequency.

 

TR 3. What is pitch? What is the relationship between pitch and frequency?

 

TR 4. What is the amplitude of a sound wave? How is the intensity or loudness of a sound related to the amplitude of a sound wave?

 

TR 5. Each of the sounds described below predominantly illustrates either pitch or loudness. Classify each as one or the other according to its main feature.

1. the whine of a mosquito
2. the sound of a low note on the piano
3. the sound of a jackhammer breaking up a cement sidewalk
4. the sound of jet plane taking off
5. the growl of a dog

Loudness, Pitch, and the Organ of Corti

 

As you have read, the hair cells in the organ of Corti are sensitive to the frequency (pitch) as well as to the amplitude (loudness) of sound waves. The basilar membrane closest to the oval window (where frequency is 20 000) is narrow and stiff, as shown in the diagram below. It responds to high-frequency sound waves. The basilar membrane, by the apex of the cochlea (where frequency is 20), is wide and flexible. It responds to low-frequency sound waves.

 

 

As part of your teacher-marked assignment, you will complete a lab examining the differences between pitch and loudness. In preparation for this lab, notice in the diagram that the wider basilar membrane furthest from the oval window and closest to the tip of the cochlea responds to lower-frequency sound waves. Different hair cells are stimulated by different frequencies. In the diagram, the numbers correspond to the range of frequencies that humans can hear. In comparison to humans, dogs can hear very high sounds in the range of 40 000 Hz. Reflect on how this knowledge is used in the use of a dog whistle. Mice can hear in the range of 80 000 Hz. And elephants can hear sounds as low as 16 Hz. Hair cells at either end of the basilar membrane can be damaged over the years, and they do not regenerate. How would this damage affect your range of hearing as you age? If you guessed that the ability to hear high and low sounds deteriorates, you were right.

 

Try This

 

Choose one of the following Try This activities.

 

TR 6. Demonstrate your understanding of how sound is perceived by answering the following questions in complete sentences.

1. How is the brain able to perceive sounds of higher or lower pitch and softer or louder sounds?

2. Mice and dogs can hear sounds in the range of 40 000 to 80 000 Hz, whereas elephants hear sounds as low as 16 Hz. Describe how the cochlea of these animals might be modified in comparison to the human cochlea.

3. Why are elderly people often not able to hear very high-pitched sounds?

TR 7. Do questions 6, 18, and 19 on page 432 of the textbook.

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