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Waves
there are critical periods in an infant s life that are necessary in order to have the later ability to perceive something.
WAVES
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Before you learn about vision and hearing, you need to understand something about waves. Both of these senses make use of different types of waves. Waves are depicted in Figure 13:
Figure 13.
The amplitude of the wave is the distance between the center point of the wave and the top of the wave. The wavelength is the distance from one wave peak to the next. The crest of the wave is the top of the wave, while the trough of the wave is the bottom of the wave. The frequency of the wave is measured in hertz and is the number of waves passing through a medium per a given time period. Hertz are usually measured in cycles per second.
There is a spectrum of waves called the electromagnetic spectrum. Visible waves are just a part of this spectrum and represents those electromagnetic waves that can actually be seen by the human eye. Figure 14 shows the electromagnetic spectrum and where visible light falls:
Figure 14.
You should know that the visible spectrum refers specifically to humans. Bees, for example, can detect ultraviolet waves, while certain snakes have the ability to detect waves in the infrared spectrum.
The different wavelengths in the visual electromagnetic spectrum are associated with different colors of light. Red has the longest wavelength, while purple has the shortest wavelength. They extend from one color to the next in a rainbow pattern. The intensity of light is determined by the amplitude of the wave.
Sound waves are basically similar to light waves. They have a much longer wavelength with high-frequency sounds being high pitched, while low-frequency sounds are low pitched. There is a wide range of what can be perceived by the human ear, between 20 and 20,000 Hertz. The most sensitive frequencies are in the middle of the range of possible sound waves. Different animal species are sensitive to different ranges of sound waves.
The amplitude of a sound wave determines its loudness. Loudness is measured in decibels, with most conversation about sixty decibels. Very loud sounds heard for an extended period of time are believed to be harmful to the ears and can result in permanent damage to the hearing.
