The human vowel and animal vocalization contain periodic and nonperiodic elements. The latter are the noise and the former are harmonic component frequencies that are multiples of the fundamental frequency. The human and animals are thought to recognize their sounds by detecting the distribution of the amplitude of the component frequencies. The question of how to process the sound information in the level of a single neuron is still open. A change of intervals of component frequencies is perceived as a change in pitch and this pitch perception has been reported to be perceived by higher vertebrate, for example, humans, monkeys, and cats. Although it has been proposed that the pitch perception result from central processing, little is known about the neural mechanism. To elucidate the neural mechanism of sound processing, we will record neural activities from auditory cortex in alert cat and examine their responses to pure tone or complex tone, by using electrophysiological techniques.