8,000hz everone in the room could hear the noise. when they play it.at 12,000hz paticipants in the age group of 41 to 71 could not hear the noise but the group from 8 to 40 could still hear it, finally they play it at 18,000hz and only the participants group from age 8 to 12 could hear the noise .this experiment showed that the higher the frequency gets the younger you have to be to hear it .their scientific explanation relates to what we learned on chapter 3 about perception of loudness and pitch to the human ear.they explain that sounds are vibration in the air ,the sound we lisent to is determined by patterns of neurones firing in the brain is translated by an air vibration into an electrical neural signal picked up by microscopic hair cell in our ear system that deteriorate when humans aged.the second test was to determined which age group was more awared behind the driving wheels,as they test two difernt drivers from two diferent age groups one was twenty two the other one was forty five they had al kinds of divercion to make them crash including objects throwng at them and people walking to