Understanding Psychology (10th Ed)

116 Chapter 
4 
Sensation and Perception
example, the lowest frequency that humans are capable of hearing is 20 cycles per 
second. Higher frequencies are heard as sounds of higher pitch. At the upper end of 
the sound spectrum, people can detect sounds with frequencies as high as 20,000 
cycles per second. 
Amplitude is a feature of wave patterns that allows us to distinguish between 
loud and soft sounds. Amplitude is the spread between the up-and-down peaks and 
valleys of air pressure in a sound wave as it travels through the air. Waves with small 
peaks and valleys produce soft sounds; those with relatively large peaks and valleys 
produce loud sounds. 
We are sensitive to broad variations in sound amplitudes. The strongest sounds 
we are capable of hearing are over a trillion times as intense as the very weakest 
sound we can hear. This range is measured in decibels . When sounds get higher than 
120 decibels, they become painful to the human ear. 
Our sensitivity to different frequencies changes as we age. For instance, as we 
get older, the range of frequencies we can detect declines, particularly for high-
pitched sounds. This is why high school students sometimes choose high-pitched 
ring tones for their cell phones in settings where cell phone use is forbidden: the 
ringing sound goes undetected by their aging teachers (Vitello, 2006) (see Figure 3). 
Sorting Out Theories of Sound 
How are our brains able to sort out wavelengths of 
different frequencies and intensities? One clue comes from studies of the basilar 
membrane, the area in the cochlea that translates physical vibrations into neural 
impulses. It turns out that sounds affect different areas of the basilar membrane, 
depending on the frequency of the sound wave. The part of the basilar membrane 
nearest to the oval window is most sensitive to high-frequency sounds, and the part 
nearest to the cochlea’s inner end is most sensitive to low-frequency sounds. This 
fi nding has led to the