When vibrations are carried through the fluid of the cochlea, they displace the basilar membrane and the hair cells upon it. This generates impulses in the nerve endings lying nearby. The impulses are carried by way of the auditory nerve to the temporal lobe of the brain. 79 Figure 8. They are less sure, however, of the mechanism which gives us information about the frequency of the sounds we hear.
Current belief is that the mechanism for pitch discrimination is located in the cochlea.
Place Theories Place theories state that certain points along the basilar membrane are sensi- only to certain frequencies. It was later found, though, that the entire cochlea was filled with fluid, so that fibers could not vibrate at frequencies as high as some sound waves we hear. A more recent place theory is the traveling-wave theory. This theory says that since the basilar membrane decreases in thickness as it spirals toward the center of the cochlea, different parts of the membrane itself will vibrate more at specific frequencies. 80 Figure 9.