Hypersonic Effect
A term coined to describe a phenomenon reported in a controversial scientific study which claims that, although humans cannot consciously hear ultrasound (sounds at frequencies above approximately 20 kHz), the presence or absence of those frequencies has a measurable effect on their physiological and psychological reactions.
Origin
Tsutomu Oohashi and colleagues formally named the effect in a 2000 paper published in the Journal of Neurophysiology. Working in Japan with the ultrasonic-rich gamelan music of Bali, the team measured brain electrical activity in listeners exposed to sound with and without frequencies above 22 kHz. The study arrived amid industry interest in high-resolution audio formats, giving it both scientific and commercial relevance.