Introduction to the special issue on perception and production of sounds in the high-frequency range of human speecha).

The frequency range audible to humans can extend from 20 Hz to 20 kHz, but only a portion of this range-the lower end up to 8 kHz-has been systematically explored because extended high-frequency (EHF) information above this low range has been considered unnecessary for speech comprehension. This special issue presents a collection of research studies exploring the presence of EHF information in the acoustic signal and its perceptual utility. The papers address the role of EHF hearing in auditory perception, the impact of EHF hearing loss on speech perception in specific populations and occupational settings, the importance of EHF in speech recognition and in providing speaker-related information, the utility of acoustic EHF energy in fricative sounds, and ultrasonic vocalizations in mice in relation to human hearing. Collectively, the research findings offer new insights and converge in showing that not only is EHF energy present in the speech spectrum, but listeners can utilize EHF cues in speech processing and recognition, and EHF hearing loss has detrimental effects on perception of speech and non-speech sounds. Together, this collection challenges the conventional notion that EHF information has minimal functional significance.