A series of experiments was conducted concerning the effect of amplitude-modulated (AM) sounds on the impression of broad-band noise. The following results were found:(1) AM sounds in broad-band noise were detected when S/N was around zero (S: the level of AM sound, N: 1/3 octave band level of broad-band noise with center frequency corresponding to the carrier frequency of AM sounds). Close examination showed that carrier frequency, modulation frequency and modulation depth had a systematic effect on the detection of AM sounds.(2) The loudness of broad-band noise mixed with AM sounds could be approximately evaluated by loudness level based on ISO 532B (LLz).(3) The timbre of broad-band noise mixed with AM sounds was judged to be more metallic as the carrier frequency of AM sounds became higher and to be more clamorous as the carrier frequency became lower. This suggests that the timbre is deteriorated when AM sounds are mixed with broad-band noise. The three factors were extracted by the factor analysis: they were “metallic” or “unpleasant, ” “powerful” and “rough.”

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In English speaking cultures, it has been reported that when auditory speech is presented in synchrony with discrepant visual (lip-read) speech, the subjects often report hearing sounds that integrate information from the two modalities (the “McGurk effect”). However, Sekiyama and Tohkura recently showed that Japanese subjects are less influenced by discrepant visual cues than Americans. This study examined the interlanguage differences in terms of the relationship between the magnitude of the McGurk effect and the frequency of incompatibility. The stimulus materials were ten syllables (/ba, pa, ma, wa, da, ta, na, ga, ka, ra/) pronounced by a Japanese and an American speaker. The ten auditory and ten visual syllables pronounced by a speaker were cross-dubbed resulting in 100 auditory-visual stimuli. Japanese syllables were presented to 14 Japanese and 10 American subjects. English syllables were presented to different groups of subjects, 12 Japanese and 10 American. The stimuli were presented in both quiet and noise-added conditions. The subjects were asked to check incompatibility between what they heard and what they saw as well as to report what they heard. The results showed that the magnitude of the McGurk effect correlated highly negatively with the frequency of incompatibility. It was suggested that the small McGurk effect in the Japanese subjects listening to Japanese speech is due to the higher sensitivity of the Japanese to auditory-visual discrepancy.

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The threshold of hearing for pure tone under free field listening conditions were measured to prepare basic data for a full-scale revision of the international standard ISO 226. The frequency range for the measurements was 31.5 Hz-16 kHz. Number of subjects was 16-69 depending on stimulus frequency. The following features are shown by comparing our data with others.(1) The thresholds of hearing do not have any great difference from other data, but some systematic deviations from ISO 226 are observed, i. e., our data are 2-6 dB higher at frequencies below 160 Hz and 1-3 dB lower at frequencies between 400 Hz and 6.3 kHz.(2) A small peak between 1 kHz and 2 kHz is observed in our results, while the peak can not be seen clearly in other data. Supplementary experiments show that the frequency characteristic of the threshold of hearing significantly correlates with head transfer function in a frequency range between 1 kHz and 8 kHz, and it suggests that the small peak mentioned above is attributable to a dip in head transfer function. But this small peak was affected by head movement of a subject.

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The purpose of this study was to examine response patterns of neurons in the primary auditory cortex of the Japanese monkey anesthetized with nitrous oxide for better understanding sound processings in the central auditory system. White noise bursts and tone bursts were used as stimuli. Major findings are that neurons in the primary auditory cortex show 1) antero-posterior tonotopicity at threshold level, 2) complicated temporal response patterns depending on frequency and/or intensity at suprathreshold level and 3) few ON-responses. Results suggest that a neuron in the primary auditory cortex may respond to different frequencies by using different temporal response patterns; namely, different frequencies may be encoded during different time intervals. More, the present data imply the capability that a neuron in the primary auditory cortex may facilitatively respond to a complicated sound composed of sequentially presented different frequencies, such as speech sounds and natural sounds. Relationships between unit activities and the auditory evoked responses, including the auditory evoked neuromagnetic field, will be also discussed.

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A possible method for the successive presentation of signals from two discretely located loudspeakers was investigated as a way to audibly simulate the sound field of a moving sound image. The results of two psychological experiments indicated that the continuous movement of a sound image could be perceived even if the signals were emitted successively with a temporal gap from two discretely located loudspeakers. In addition, it was perceived more easily as the duration of a signal increased and as the temporal gap decreased. The threshold of the perceptibility of the continuous movement seems to be related to that of the temporal gap detection.

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