. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. 482 Comparative Animal Physiology Intensity Discrimination. The mechanism for the perception of intensity is apparently ; With increasing intensity of a given frequency there is: (1) an increase of the frequency of impulses in single nerve fibers, espe- cially for high frequencies; (2) an increase in the number of fibers which carry impulses. As the vibrations increase in amplitude a wider and wider band of sense cells responds. At low frequencies the impulses of a single fiber have a one-to-one corres
. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. 482 Comparative Animal Physiology Intensity Discrimination. The mechanism for the perception of intensity is apparently ; With increasing intensity of a given frequency there is: (1) an increase of the frequency of impulses in single nerve fibers, espe- cially for high frequencies; (2) an increase in the number of fibers which carry impulses. As the vibrations increase in amplitude a wider and wider band of sense cells responds. At low frequencies the impulses of a single fiber have a one-to-one correspondence to the pressure waves of the stimulus. This is true below 500 cycles for the initial waves and at the frequency of 200 cycles with equilibration. However, above these sound frequencies the frequency of impulses varies with intensity. For example, at 7000 cycles (Fig. 160) the frequency of discharge of a single fiber may increase from less than 10 to as much as 135 per second as the intensity is increased from -82 to -30 db below a given reference level. It can also be seen from Figure. 5000 sooo 6000 7000 Sound Frequency Fig. 160. Curves showing the relation between frequency of spike potential discharge of a single auditory nerve fiber and the intensity and frequency of the sound stimulus. Note that with increasing intensity the fiber responds to a greater frequency band, and, at each frequency, with a greater frequency of spike potential discharge. After Galambos and Davis," from Fulton .^^ 160 that although this one fiber was responsive only at frequencies very close to 7000 cycles at -78 and -82 db it was responsive to all frequencies between 5000 and 8000 at -20 db, with, however, a maximal response still at 7000. Sound Localization. One important function of the human ear, in addi- tion to discrimination of frequency and intensity, is that of localization of of sound. A person with normal hearing is able to locate sounds with a surprising degree o
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