Waves and Wavelengths
By the end of this section, you will be able to:
Describe important physical features of wave forms
Show how physical properties of light waves are associated with perceptual experience
Show how physical properties of sound waves are associated with perceptual experience
Visual and auditory stimuli both occur in the form of waves. Although the two stimuli are very different in terms of composition, wave forms share similar characteristics that are especially important to our visual and auditory perceptions. In this section, we describe the physical properties of the waves as well as the perceptual experiences associated with them.
Amplitude And Wavelength
Two physical characteristics of a wave are amplitude and wavelength ([link]). The amplitude{: data-type=“term”} of a wave is the height of a wave as measured from the highest point on the wave (peak{: data-type=“term”} or crest{: data-type=“term”}) to the lowest point on the wave (trough{: data-type=“term”}). Wavelength{: data-type=“term”} refers to the length of a wave from one peak to the next.
{: #Figure_05_02_Wave}
Wavelength is directly related to the frequency of a given wave form. Frequency{: data-type=“term”} refers to the number of waves that pass a given point in a given time period and is often expressed in terms of hertz (Hz){: data-type=“term”}, or cycles per second. Longer wavelengths will have lower frequencies, and shorter wavelengths will have higher frequencies ([link]).
{: #Figure_05_02_Frequencies}
Light Waves
The visible spectrum is the portion of the larger electromagnetic spectrum that we can see. As [link] shows, the electromagnetic spectrum encompasses all of the electromagnetic radiation that occurs in our environment and includes gamma rays, x-rays, ultraviolet light, visible light, infrared light, microwaves, and radio waves. The visible spectrum in humans is associated with wavelengths that range from 380 to 740 nm—a very small distance, since a nanometer (nm) is one billionth of a meter. Other species can detect other portions of the electromagnetic spectrum. For instance, honeybees can see light in the ultraviolet range (Wakakuwa, Stavenga, & Arikawa, 2007), and some snakes can detect infrared radiation in addition to more traditional visual light cues (Chen, Deng, Brauth, Ding, & Tang, 2012; Hartline, Kass, & Loop, 1978).
{: #Figure_05_02_Spectrum}
In humans, light wavelength is associated with perception of colour ([link]). Within the visible spectrum, our experience of red is associated with longer wavelengths, greens are intermediate, and blues and violets are shorter in wavelength. (An easy way to remember this is the mnemonic ROYGBIV: red, orange, yellow, green, blue, indigo, violet.) The amplitude of light waves is associated with our experience of brightness or intensity of colour, with larger amplitudes appearing brighter.
{: #Figure_05_02_VisSpec}
Sound Waves
Like light waves, the physical properties of sound waves are associated with various aspects of our perception of sound. The frequency of a sound wave is associated with our perception of that sound’s pitch. High-frequency sound waves are perceived as high-pitched sounds, while low-frequency sound waves are perceived as low-pitched sounds. The audible range of sound frequencies is between 20 and 20000 Hz, with greatest sensitivity to those frequencies that fall in the middle of this range.
As was the case with the visible spectrum, other species show differences in their audible ranges. For instance, chickens have a very limited audible range, from 125 to 2000 Hz. Mice have an audible range from 1000 to 91000 Hz, and the beluga whale’s audible range is from 1000 to 123000 Hz. Our pet dogs and cats have audible ranges of about 70–45000 Hz and 45–64000 Hz, respectively (Strain, 2003).
The loudness of a given sound is closely associated with the amplitude of the sound wave. Higher amplitudes are associated with louder sounds. Loudness is measured in terms of decibels (dB){: data-type=“term”}, a logarithmic unit of sound intensity. A typical conversation would correlate with 60 dB; a rock concert might check in at 120 dB ([link]). A whisper 5 feet away or rustling leaves are at the low end of our hearing range; sounds like a window air conditioner, a normal conversation, and even heavy traffic or a vacuum cleaner are within a tolerable range. However, there is the potential for hearing damage from about 80 dB to 130 dB: These are sounds of a food processor, power lawnmower, heavy truck (25 feet away), subway train (20 feet away), live rock music, and a jackhammer. The threshold for pain is about 130 dB, a jet plane taking off or a revolver firing at close range (Dunkle, 1982).
Although wave amplitude is generally associated with loudness, there is some interaction between frequency and amplitude in our perception of loudness within the audible range. For example, a 10 Hz sound wave is inaudible no matter the amplitude of the wave. A 1000 Hz sound wave, on the other hand, would vary dramatically in terms of perceived loudness as the amplitude of the wave increased.
See also
Watch this brief video demonstrating how frequency and amplitude interact in our perception of loudness.
Of course, different musical instruments can play the same musical note at the same level of loudness, yet they still sound quite different. This is known as the timbre of a sound. Timbre refers to a sound’s purity, and it is affected by the complex interplay of frequency, amplitude, and timing of sound waves.
Summary
Both light and sound can be described in terms of wave forms with physical characteristics like amplitude, wavelength, and timbre. Wavelength and frequency are inversely related so that longer waves have lower frequencies, and shorter waves have higher frequencies. In the visual system, a light wave’s wavelength is generally associated with colour, and its amplitude is associated with brightness. In the auditory system, a sound’s frequency is associated with pitch, and its amplitude is associated with loudness.
Which of the following correctly matches the pattern in our perception of colour as we move from short wavelengths to long wavelengths?
red to orange to yellow
yellow to orange to red
yellow to red to orange
orange to yellow to red
Check Answer
B
The visible spectrum includes light that ranges from about ________.
400–700 nm
200–900 nm
20–20000 Hz
10–20 dB
Check Answer
A
The electromagnetic spectrum includes ________.
radio waves
x-rays
infrared light
all of the above
Check Answer
D
The audible range for humans is ________.
380–740 Hz
10–20 dB
less than 300 dB
20-20,000 Hz
Check Answer
D
The quality of a sound that is affected by frequency, amplitude, and timing of the sound wave is known as ________.
pitch
tone
electromagnetic
timbre
Check Answer
D
Critical Thinking Questions
Why do you think other species have such different ranges of sensitivity for both visual and auditory stimuli compared to humans?
Why do you think humans are especially sensitive to sounds with frequencies that fall in the middle portion of the audible range?
Once again, one could make an evolutionary argument here. Given that the human voice falls in this middle range and the importance of communication among humans, one could argue that it is quite adaptive to have an audible range that centers on this particular type of stimulus.
Personal Application Question
Hint
text
If you grew up with a family pet, then you have surely noticed that they often seem to hear things that you don’t hear. Now that you’ve read this section, you probably have some insight as to why this may be. How would you explain this to a friend who never had the opportunity to take a class like this?
- amplitude
height of a wave ^
- decibel (dB)
logarithmic unit of sound intensity ^
- electromagnetic spectrum
all the electromagnetic radiation that occurs in our environment ^
- frequency
number of waves that pass a given point in a given time period ^
- hertz (Hz)
cycles per second; measure of frequency ^
- peak
(also, crest) highest point of a wave ^
- pitch
perception of a sound’s frequency ^
- timbre
sound’s purity ^
- trough
lowest point of a wave ^
- visible spectrum
portion of the electromagnetic spectrum that we can see ^
- wavelength
length of a wave from one peak to the next peak
Copyright Notice
This work is (being) adapted from on OpenStax Psychology 2e which is licensed under creative commons attribution 4.0 license. We license our work under a similar license. If you copy, adapt, remix or build up on work, you must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.