Hypersonic effect

Abstract: The hypersonic effect is a phenomenon in which sounds containing significant quantities of non-stationary high-frequency components (HFCs) above the human audible range (max. 20 kHz) activate the midbrain and diencephalon and evoke various physiological, psychological and behavioral responses. Yet important issues remain unverified, especially the relationship existing between the frequency of HFCs and the emergence of the hypersonic effect. In this study, to investigate the relationship between the hypersonic effect and HFC frequencies, we divided an HFC (above 16 kHz) of recorded gamelan music into 12 band components and applied them to subjects along with an audible component (below 16 kHz) to observe changes in the alpha2 frequency component (10–13 Hz) of spontaneous EEGs measured from centro-parieto-occipital regions (Alpha-2 EEG), which we previously reported as an index of the hypersonic effect. Our results showed reciprocal directional changes in Alpha-2 EEGs depending on the frequency of the HFCs presented with audible low-frequency component (LFC). When an HFC above approximately 32 kHz was applied, Alpha-2 EEG increased significantly compared to when only audible sound was applied (positive hypersonic effect), while, when an HFC below approximately 32 kHz was applied, the Alpha-2 EEG decreased (negative hypersonic effect). These findings suggest that the emergence of the hypersonic effect depends on the frequencies of inaudible HFC.

Abstract: High-resolution audio has a higher sampling frequency and a greater bit depth than conventional low-resolution audio such as compact disks. The higher sampling frequency enables inaudible sound components (above 20 kHz) that are cut off in low-resolution audio to be reproduced. Previous studies of high-resolution audio have mainly focused on the effect of such high-frequency components. It is known that alpha-band power in a human electroencephalogram (EEG) is larger when the inaudible high-frequency components are present than when they are absent. Traditionally, alpha-band EEG activity has been associated with arousal level. However, no previous studies have explored whether sound sources with high-frequency components affect the arousal level of listeners. The present study examined this possibility by having 22 participants listen to two types of a 400-s musical excerpt of French Suite No. 5 by J. S. Bach (on cembalo, 24-bit quantization, 192 kHz A/D sampling), with or without inaudible high-frequency components, while performing a visual vigilance task. High-alpha (10.5-13 Hz) and low-beta (13-20 Hz) EEG power were larger for the excerpt with high-frequency components than for the excerpt without them. Reaction times and error rates did not change during the task and were not different between the excerpts. The amplitude of the P3 component elicited by target stimuli in the vigilance task increased in the second half of the listening period for the excerpt with high-frequency components, whereas no such P3 amplitude change was observed for the other excerpt without them. The participants did not distinguish between these excerpts in terms of sound quality. Only a subjective rating of inactive pleasantness after listening was higher for the excerpt with high-frequency components than for the other excerpt. The present study shows that high-resolution audio that retains high-frequency components has an advantage over similar and indistinguishable digital sound sources in which such components are artificially cut off, suggesting that high-resolution audio with inaudible high-frequency components induces a relaxed attentional state without conscious awareness.

Abstract: Reiko Yagi , Emi Nishina and Tsutomu Oohashi The Graduate University for Advanced Studies, Shonan Village Center, Hayama-cho, Miura-gun, Kanagawa, 240–0193 Japan National Institute of Multimadia Education, 2–12, Wakaba, Mihama-ku, Chiba, 261–0014 Japan Chiba Institute of Technology, 2–17–1, Tsudanuma, Narashino, Chiba, 275–0016 Japan ATR Human Information Science Laboratories, 2–2–2, Hikaridai, “Keihanna Science City”, Kyoto, 619–0288 Japan

Abstract: Although it is generally accepted that humans cannot perceive sounds in the frequency range above 20 kHz, the question of whether the coexistence of such “inaudible” high-frequency components (HFC) with audible low-frequency components (LFC) may have any biological effects on listeners remains unanswered. We have attempted to address this complex problem using a multidisciplinary approach: combined evaluation of physiological, psychological and behavioral responses. Physiological measurement revealed that the combined presentation of the HFC and LFC, compared with the presentation of the only LFC, significantly increased the power of the occipital alpha-EEG in parallel with the rCBF in the brainstem and left thalamus. The power of the occipital alpha-EEG correlated significantly with the rCBF in the left thalamus. Psychological evaluation indicated that the subjects felt the sound containing HFC to be more pleasant than the only LFC. Behavioral evaluation showed that the subjects spontaneously adjusted the volume of the sound level at a greater magnitude when listening to the sound containing HFC compared with the only LFC. The line of evidence suggests the existence of a previously unrecognized response to complex sound containing particular types of high frequencies above the audible range. We term this phenomenon the “hypersonic effect.”