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Ch. 4 S. 3 1 Chapter 4 Section 3 Hearing Obj: Describe how the _______ perceives ________________ Sound travels through the air in _________________. It is caused by changes in air pressure that result from _____________________. Anything that makes a sound causes vibrations. Each of these vibrations is called a cycle or a sound wave. Every _____________ has its own pitch and loudness. Pitch Sound waves can be very fast, occurring many times per second. The _______________ of a soundhow high or low the sound is-depends on its frequency, or the number of cycles per second. The more cycles per second, the higher the pitch of a sound. Women’s voices usually have a higher pitch than those of men because women’s ______________ cords tend to be shorter and therefore ________________ at a greater frequency. The human ______ can hear sound waves that vary from 20 to 20,000 cycles per second. Many animals, including dogs and ___________________, hear sounds well beyond 20,000 cycles per second. Although we cannot hear them, the sounds emitted by dolphins help them locate others. The sound ________________ echo back from fish and other objects. Loudness What is the _______________ sound you can hear? What is the loudest? The loudness of a sound is determined by the height, or amplitude, of sound waves. The higher the _________________ of the wave, the louder the sound. The loudness of a sound is measured in ________________, a unit that is abbreviated dB. Zero dB is considered the threshold of hearing. Zero dB is about as loud as the ticking of a watch 20 feet away in a very quiet room. The Ear Just as the eye is the human instrument for _________________, the ear is the instrument for sensing all the sounds around us. In fact, the ear is shaped to capture sound waves, to __________________ with them, and to transmit sound to the brain. What we normally think of as the ear is actually the outer ear. We also have a middle ear and an ____________ ear. The ____________________ is the gateway from the outer ear to the middle ear. It is a thin _______________ that vibrates when sound waves strike it. As it vibrates, it transmits the sound to three small bones in the middle ear: the hammer, the anvil, and the _______________. (The stirrup is the smallest bone in the human body). These bones then also begin to vibrate and transmit sound to the inner ear. The inner ear consists of the cochlea. The word cochlea comes from the Greek word for “snail”. The __________________ is a bony tube that contains fluids as well as neurons that move in response to the vibrations of the fluids. The movement generates neural impulses that are transmitted to the brain via the _______________ nerve. Within the brain, auditory input is projected onto the hearing areas of the ______________ cortex. Deafness Not everyone perceives ______________. About 2 million Americans are _________. Deafness may be __________________ or caused by disease, injury, or old age. • ____________________ Deafness – If we see an older person with a hearing ________, we can assume that he or she is probably suffering from conductive deafness. Conductive deafness occurs because of _______________ to the middle ear. Since this part of the ear amplifies sounds, damage to it prevents people from hearing sounds that are not loud enough. Fortunately, people Ch. 4 S. 3 2 with conductive deafness are often helped by hearing aids. These aids provide the _________________ that the middle ear does not. • __________________________ Deafness – Many people do not perceive sounds of certain ________________. This is a sign of sensorineural deafness. Sensorineural deafness is usually caused by damage to the inner ear. Most often, the neurons in the cochlea are destroyed. Sometimes sensorineural deafness is due to damage to the auditory nerve, either through _______________ or through prolonged exposure to very loud sounds. Have you ever attended a high-volume rock concert and left with a ringing sensation in your ears? This may have meant that ___________________ had been destroyed in your ears. The same thing can happen to workers who operate certain drilling equipment or drive loud vehicles. The next time you are exposed to loud ___________, remember to cover your ears. Devices called experimental cochlear implants, or “artificial ears,” contain microphones that sense sounds and electronic equipment that stimulates the auditory nerve directly. However, if the auditory nerve itself is damaged, a cochlear ____________ cannot help. • Deafness in the World ___________ – In recent years, people who are ________ have been able to come more into the mainstream of sensory experience as a result of their own efforts, the efforts of others, and new technology. Heather Whitestone became Miss ___________________ in 1995. __________________ are often on hand to translate speeches into languages (such as American Sign Language) used by members of the audience who are hearing impaired. More and more schools are offering courses in American Sign Language. Many television shows are now “closed captioned,” which means that special ________________ make captions of dialogue visible on the screen. And, as you have just read, scientists are always trying to find new ways to counteract ______________ inside the ear.