Brainstem encoding of speech in the extended high frequencies and its behavioral correlates

Whether the auditory nervous system can extract and use speech information carried in the extended high-frequency (EHF; >8 kHz) range is an unresolved question in auditory neuroscience. Although EHF sensitivity is increasingly recognized as important for speech perception, it is unclear whether EHF hearing is directly or indirectly involved in real-world listening. This study examined brainstem neural encoding of EHF speech components and the relationship between EHF hearing sensitivity and both neural and perceptual speech processing. Envelope following responses (EFRs) to broadband and high-pass filtered (>4 kHz and >8 kHz) speech stimuli, along with digits-in-noise speech recognition thresholds under various masking conditions (broadband, <2 kHz, <4 kHz, <8 kHz), were measured in 47 normal-hearing adults. Our findings suggest that the auditory brainstem can phase-lock to temporal speech features carried in the EHF region (<i>f₀</i> and <i>f₀</i> modulation). Furthermore, participants with poorer EHF sensitivity showed weaker EFR <i>f₀</i> amplitudes for both broadband and >4 kHz speech stimuli, as well as overall elevated speech recognition thresholds. EHF thresholds predicted both speech neural encoding strength and speech-in-noise performance, particularly under low-pass masking conditions. These results demonstrate that speech information carried in the EHF range weakly encodes important cues for speech perception, such as voice <i>f₀</i> and <i>f₀</i> modulation. Furthermore, poorer EHF hearing is associated with degraded neural encoding and perception of signals with dominant energy in the standard frequency range (<8 kHz).<b>NEW & NOTEWORTHY</b> This study provides the first evidence that the auditory nervous system can extract important temporal speech features (<i>f₀</i> and <i>f₀</i> modulation) from the extended high-frequency (EHF) region. Individuals with EHF loss exhibit weaker neural encoding of broadband and high-frequency speech stimuli, suggesting EHF deficits broadly affect neural transduction. These results advance understanding of EHF contributions to speech processing and demonstrate that EHF hearing sensitivity is linked to neural transduction and perception of broadband speech signals.