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TEXT K
First read the following questions.
89. What is the function of the electrodes mentioned in the passage?
A. They detect the clicks sounds.
B. They transmit the clicks to the computer.
C. They detect electrical activity in the brain.
D. They stimulate the auditory nervous system.
正确答案是
90. The function of the computer in this test is _____.
A. to amplify electrical signals
B. to transform electrical signals into sounds
C. to send electrical signals through the earphones
D. to transform electrical signals into a printed pattern
正确答案是
Now read Text K quickly and select your answers.
Until recently, because of the difficulty of testing hearing in a small children, deafness often wasn't detected until a child was about two, too late to prevent a permanent language handicap. Now, however, there is a method to test infants' hearing by measuring electrical activity generated by the brain stem in response to sound. Through earphones, an infant is presented with a series of clicking sounds that stimulate the auditory nervous system. The electrical activity thus evoked in the brain is in turn picked up by electrodes placed behind each ear. These electrical signals are amplified, fed into a computer and printed out as waves on a graph. Within 12.5 milliseconds of a click, the graph of a normal baby will show seven distinct peaks, each representing a point along the path the sound has taken from the auditory nerve to the hearing centers of the cortex. For a baby with impaired hearing, peaks take longer to appear. different types of hearing defects, moreover, will produce wave patterns that deviate from the normal characteristic ways. for example, absence of all seven waves indicates total sensory-neural deafness, usually untreatable. In conductive deafness, which can be treated, wave patterns will emerge if the intensity of the sound is increased.