SCN3230-ABED_1: Module 1 Lesson 3 - 4

Lesson 3 — Mechanoreception: The Ear

Pitch and Loudness

Read pages 421 - 424

You likely have been to a concert or have listened to your iPod, or perhaps you play a musical instrument. Probably, you are familiar with high-pitched and low-pitched sounds. However, do you know how or why you are able to hear sounds of high or low pitch ? How are you able to distinguish between yelling and whispering?

Sound involves mechanical vibration waves of pressure and displacement. When describing the properties of sound, we normally consider two criteria: frequency and amplitude. Frequency is the number of vibrations in a given unit of time. Frequency is the property of sound that determines pitch, which is the degree of highness or lowness of a sound. (In music, pitch is used to mean the same as frequency.) Amplitude refers to the distance from the rest position to the crest of the sound wave; as the amplitude increases, the sound becomes louder.

Try This

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

Whine of a mosquito
Sound of a low note on the piano
Sound of a jackhammer breaking a cement sidewalk
Sound of jet plane taking off
Growl of a dog

Check Your Work.

Pitch
Pitch
Loudness
Loudness
Pitch

Loudness, Pitch, and the Organ of Corti

Alberta Education

You read on pages 421 to 424 that 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 Hz) is narrow and stiff. It responds to high frequency sound waves. The basilar membrane by the apex or tip of the cochlea (where frequency is 20 Hz) is wide and flexible. It responds to low frequency sound waves.

On the next page of this lesson, you will examine the differences between pitch and loudness. Notice in the diagram that the wider basilar membrane furthest from the oval window and closest to the apex or tip of the cochlea responds to lower frequency sound waves. Various hair cells are stimulated by various frequencies. In the diagram, the numbers correspond to the range of frequencies that humans can hear.

Much different than humans, dogs hear very high sounds in the range of 40,000 Hz. Reflect on how we use this knowledge in a dog whistle. Mice can hear in the range of 80,000 Hz. 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 might this damage affect the range of hearing as people age? If you guessed that the ability to hear high and low sounds deteriorates, you were right.

Watch This

To review how the organ of Corti distinguishes pitch and loudness, you may wish to view this video. Observe the animated clip showing the oscillations of the basilar membrane at various sound frequencies.

Self-Check

Demonstrate your understanding of the concepts of how sound is perceived by responding to the following questions.

How is the brain able to perceive sounds of higher or lower pitch and softer or louder sounds?
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 different than the human cochlea.
Why are elderly people often unable to hear high-pitched sounds?

Check Your Work.

Self-Check Answers

Higher pitch stimulates neurons closest to the oval window, and lower pitch stimulates neurons furthest from the oval window. Loud sound stimulates a larger number of neurons and softer sound stimulates a smaller number of neurons.

The base is closer to oval window (where hear high pitch ) and the apex or tip is farther from the oval window (where hear low pitch) so would predict that dogs and mice who hear high frequencies would have a larger base and elephants who hear lower frequencies would have larger apex.

Note that other factors such as number of turns in the cochlea and its size and shape also affect the frequency that an animal can detect.

Age-related hearing loss occurs naturally and affects the hair cells in the high frequency area. Noise-induced hearing loss occurs through long-term exposure to very loud sounds. Damaged hair cells do not regenerate, and hearing is diminished permanently.