Envelope frequency following responses are stronger for high-pass than low-pass filtered vowels

Background: To assess hearing in response to speech, the envelope frequency following response (FFR) can be observed at the fundamental frequency of a vowel stimulus, and its harmonics. FFRs are complex non-linear phenomena, which require better understanding for allowing robust inferences on the assessment of hearing and hearing aid fitting. Objectives: To evaluate the effect of stimulus bandwidth on FFR detection rates using filtered vowel stimuli with equal sound levels. Design: FFRs were collected whilst presenting repeated vowels (in consonant-vowel-consonant format) filtered into different bandwidths. Eighty stimuli per word were presented at 70 dB SPL LAeq through insert earphones with an inter-stimulus interval of 1s. Responses were detected using frequency-domain Hotelling’s T2 (HT2) tests for individual multiples of the fundamental frequency (F0) and for combinations of F0 multiples. Study Sample: Eleven native English-speaking subjects with normal hearing thresholds. Results: Average detection rates are highest (69%) with stimuli high-pass filtered >1000 Hz, and significantly lower for low-pass filtered stimuli (40%). Conclusion: High-pass filtered vowels elicit stronger FFRs than low-pass filtered vowels at the same dB SPL LAeq. For testing hearing using band-limited speech, filtering effects (due to hearing loss, hearing aid setting or stimulus choice) on responses must be considered

Gaussian Processes for hearing threshold estimation using Auditory Brainstem Responses

The Auditory Brainstem Response (ABR) plays an important role in diagnosing and managing hearing loss, but can be challenging and time-consuming to measure. Test times are especially long when multiple ABR measurements are needed, e.g., when estimating hearing threshold at a range of frequencies. While many detection methods have been developed to reduce ABR test times, the majority were designed to detect the ABR at a single stimulus level and do not consider correlations in ABR waveforms across levels. These correlations hold valuable information, and can be exploited for more efficient hearing threshold estimation. This was achieved in the current work using a Gaussian Process (GP), i.e., a Bayesian approach method for non-linear regression. The function to estimate with the GP was the ABR's amplitude across stimulus levels, from which hearing threshold was ultimately inferred. Active learning rules were also designed to automatically adjust the stimulus level and efficiently locate hearing threshold. Simulation results show test time reductions of up to $\sim$50% for the GP compared to a sequentially applied Hotelling's T2 test, which does not consider correlations across ABR waveforms. A case study was also included to briefly assess the GP approach in ABR data from an adult volunteer

Exploration of inter-individual variability in cortical responses to natural English sentences

Objectives: Grand average cortical responses to speech have shown the possibility to analyse perceived intelligibility. Cortical responses to sentences are explored to determine their variability amongst subjects and therefore their applicability in clinic. Methods: EEG responses to 100 repeats of three English sentences were recorded for 16 subjects with normal hearing thresholds. Responses were detected using a Hotelling’s T2 test on 100 ms low-pass filtered (30 Hz) segments (two 50 ms features per segment). Results: Participants showed a clear response at segments including the stimulus onset (p<0.01). Later segments showed strong variability in detection between participants, with less significant responses and more repeats needed compared to onset detection. Conclusion: Onset responses to natural sentences can be detected within 100 repeats (100 s), which is relevant for clinical use. The possibility of detecting robust responses beyond the onset at an individual level need to be further investigated

Multichannel frequency-domain Hotelling's T2 test for detection of envelope following responses to natural vowels

Objectives: A multichannel frequency-domain Hotelling’s T2 (MCHT2) method for envelope following response detection is introduced and its sensitivity compared to a Fourier Analyzer (FA), Magnitude Squared Coherence (MSC), and single-channel Hotelling’s T2 (HT2). Methods: EEG data were collected from 12 normal hearing adults during auditory stimulation with 4 repeated vowels. Each stimulus was presented 220 times with both polarities. Response detection was compared between algorithms based on detection rate and time. Results: A five-channel MCHT2 showed a significantly higher detection rate compared to FA (27% increase) and MSC (24%) detection rates. Both HT2 and MCHT2 showed a significant decrease in mean detection time compared to the FA (29% and 39%, respectively). Conclusion: MCHT2 analysis improves sensitivity in the detection of envelope following responses to natural vowels compared to single-channel methods, without increasing computational complication

Pediatr Nephrol

Survival in the pediatric end-stage renal disease (ESRD) population has improved substantially over recent decades. Nonetheless, mortality remains at least 30 times higher than that of healthy peers. Patient survival is multifactorial and dependent on various patient and treatment characteristics and degree of economic welfare of the country in which a patient is treated. In this educational review, we aim to delineate current evidence regarding mortality risk in the pediatric ESRD population and provide pediatric nephrologists with up-to-date information required to counsel affected families