Abstract
In a normal listening, a complex tone is perceived as a single tone with one difinite pitch corresponding to the pitch of the fundamental frequency. However, the pitch of a complex tone consisting of a small number of higher harmonics and without the fundamental is often ambiguous. An experiment was carried out in four subjects adjusted the frequency of pure tone to match the pitch of an amplitude-modulated (AM) tone, in order to study information and the mechanism for pitch perception of tones. It was found that several different pure tones were perceived to be equal to an AM tone in pitch (Fig. 3 and Fig. 4). The frequencies of the pure tones corresponded nearly to the constituent frequencies, the combination tone frequencies of the type 2f_1-f_2 and the subharmonics of them (Fig. 4). Considering the experimental result, the pitch perception mechanism was inferred as follows: There exist two kinds of informations as the cues for pitch perception. Place information are tonotopic organization on auditory neuron layers (Fig. 5), whereas temporal information is formed by time intervals of neuronal discharges (Fig. 6). Each information provides several different cues for pitch perception. According to the folded histogram (Fig. 9), the response of an auditory primary neuron to a pure tone stimulus shows a systematic locking to the cycle for frequencies up to some 4-5kHz. On the other hand, tone chroma changes regularly with one octave periodicity for frequencies up to some 4-5kHz. However, the regularity of the relationship between frequency and chroma disappears over that frequency (Fig. 8). These physiological and psychological knowledges suggest that tone chroma is based on the synchronization between tone stimulus waveform and time pattern of neuronal discharges. Then it is inferred that pitch in a narrow sense (tone height) is mainly given rise to by the place information and tone chroma is given rise to by the temporal information (Fig. 10). The reason why several different pure tones were matched to an AM tone in pitch perception can be interpreted that the subjects perceived pitches paying attention to specific cues among many different cues (Fig. 10).
