Phase-locking to the temporal envelope of speech is associated with envelope processing and speech perception. The phase-locked activity of the auditory pathway, across modulation frequencies, is generally assessed at group level and shows a decrease in response magnitude with increasing modulation frequency. With the exception of increased activity around 40 and 80 to 100 Hz. Furthermore, little is known about the phase-locked response patterns to modulation frequencies ≤ 20 Hz, which are modulations predominately present in the speech envelope. In the present study we assess the temporal modulation transfer function (TMTF ASSR ) of the phase-locked activity of the auditory pathway, from 0.5 to 100 Hz at a high-resolution and by means of auditory steady-state responses. Although the group-averaged TMTF ASSR corresponds well with those reported in the literature, the individual TMTF ASSR shows a remarkable intersubject variability. This intersubject variability is especially present for ASSRs that originate from the cortex and are evoked with modulation frequencies ≤ 20 Hz. Moreover, we found that these cortical phase-locked activity patterns are robust over time. These results show the importance of the individual TMTF ASSR when assessing phase-locked activity to envelope fluctuations, which can potentially be used as a marker for auditory processing.

Auditory steady-state responses (ASSRs) are auditory evoked potentials that reflect phase-locked neural activity to periodic stimuli. ASSRs are often evoked by tones with a modulated envelope, with sinusoidal envelopes being most common. However, it is unclear if and how the shape of the envelope affects ASSR responses. In this study, we used various trapezoidal modulated tones to evoke ASSRs (modulation frequency = 40 Hz) and studied the effect of four envelope parameters: attack time, hold time, decay time and off time. ASSR measurements in 20 normal hearing subjects showed that envelope shape significantly influenced responses: increased off time and/or increased decay time led to responses with a larger signal-to-noise-ratio (SNR). Response phase delay was significantly influenced by attack time and to a lesser degree by off time. We also simulated neural population responses that approximate ASSRs with a model of the auditory periphery (Bruce et al. 2018). The modulation depth of the simulated responses, i.e. the difference between maximum and minimum firing rate, correlated highly with the response SNRs found in the ASSR measurements. Longer decay time and off time enhanced the modulation depth both by decreasing the minimum firing rate and by increasing the maximum firing rate. In conclusion, custom envelopes with long decay and off time provide larger response SNRs and the benefit over the commonly used sinusoidal envelope was in the range of several dB.

Objective: To investigate modifications of the Flemish Digit Triplet Test (DTT) to improve its efficiency, i.e. the use of a low-pass filtered noise and variable adaptive step sizes according to a digit scoring procedure, targeting different recognition probabilities. Design and study sample: Speech reception thresholds (SRT) were evaluated in terms of their test-retest reliability and correlation with pure tone averages (PTA) in a group of 68 adult participants with different degrees of hearing impairment. Results: The use of a low-pass filtered noise did not result in better test-retest reliability or an improved SRT-PTA correlation. Using digit scoring with adaptive step sizes parametrised to target a recognition probability of 79% (D79), corresponding to the recognition probability of the currently used DTT with triplet scoring and fixed adaptive step sizes of 2 dB, increased test-retest reliability. Lower recognition probabilities of 57 and 35% demonstrated worse reliability and worse SRT-PTA correlations. Conclusions: Given the increased test-retest reliability of D79, a similar reliability as for the currently used DTT could be obtained after considerably fewer trials, leading to a profit in test duration.

A language-independent automated self-test on tablet based on masked recognition of ecological sounds, the Sound Ear Check (SEC), was developed. In this test, 24 trials of eight different sounds are randomly presented in a noise that was spectrally shaped according to the average frequency spectra of the stimulus sounds, using a 1-up 2-down adaptive procedure. The test was evaluated in adults with normal hearing and hearing loss, and its feasibility was investigated in young children, who are the target population of this test. Following equalization of perceptual difficulty across sounds by applying level adjustments to the individual tokens, a reference curve with a steep slope of 18%/dB was obtained, resulting in a test with a high test–retest reliability of 1 dB. The SEC sound reception threshold was significantly associated with the averaged pure tone threshold ( r = .70), as well as with the speech reception threshold for the Digit Triplet Test ( r = .79), indicating that the SEC is susceptible to both audibility and signal-to-noise ratio loss. Sensitivity and specificity values on the order of magnitude of ∼70% and ∼80% to detect individuals with mild and moderate hearing loss, respectively, and ∼80% to detect individuals with slight speech-in-noise recognition difficulties were obtained. Homogeneity among sounds was verified in children. Psychometric functions fitted to the data indicated a steep slope of 16%/dB, and test–retest reliability of sound reception threshold estimates was 1.3 dB. A reference value of −9 dB signal-to-noise ratio was obtained. Test duration was around 6 minutes, including training and acclimatization.

Objectives: This study aims to investigate the large-scale applicability of the Digit Triplet test (DTT) for school-age hearing screening in fifth grade elementary (5E) (9 to 12 years old) and third grade secondary (3S) (13 to 16 years old) school children. The reliability of the test is investigated as well as whether pass/fail criteria need to be corrected for training and/or age, and whether these criteria have to be refined with respect to referral rates and pure-tone audiometry results. Design: Eleven school health service centers participated in the region of Flanders (the Northern part of Belgium). Pure-tone screening tests, which are commonly used for hearing screening in school children, were replaced by the DTT. Initial pass/fail criteria were determined. Children with speech reception thresholds (SRT) of -7.2 dB signal to noise ratio (SNR) (5E) and -8.3 dB SNR (3S) or worse were referred for an audiogram and follow-up. In total, n = 3412 (5E) and n = 3617 (3S) children participated. Results: Population SRTs (2 SD) were -9.8 (+/- 1.8) dB SNR (5E) and -10.5 (+/- 1.6) dB SNR (3S), and do not need correction for training and/or age. Whereas grade-specific pass/fail criteria are more appropriate, a linear regression analysis showed an improvement of 0.2 dB per year of the SRT until late adolescence. SRTs could be estimated with a within-measurement reliability of 0.6 dB. Test duration was also grade-dependent, and was 6min 50sec (SD = 61sec) (5E) and 5min 45sec (SD = 49sec) (3S) on average for both ears. The SRT, test reliability, and test duration were comparable across centers. With initial cut-off values, 2.9% (5E) and 3.5% (3S) of children were referred. Based on audiograms of n = 39 (5E) and n = 59 (3S) children, the diagnostic accuracy of the DTT was assessed. A peripheral hearing loss was detected in 31% (5E) and 53% (3S) of the referred children. Hearing losses found were mild. Less strict pass/fail criteria increased the diagnostic accuracy. Optimal pass/fail criteria were determined at -6.5 dB SNR (5E) and -8.1 dB SNR (3S). With these criteria, referral rates dropped to 1.3% (5E) and 2.4% (3S). Conclusions: The DTT has been implemented as the new hearing screening methodology in the Flemish school-age hearing screening program. Based on the results of this study, pass/fail criteria were determined and optimized to be used for systematic hearing screening of 5E and 3S school children. Furthermore, this study provides reference values for the DTT in children 9 to 16 years of age. Reliable SRTs can be obtained with the test, allowing accurate monitoring of hearing over time. This is important in the context of a screening guideline, which aims to identify children with noise-induced hearing loss. Validation of the screening result should go beyond taking an audiogram, as a peripheral hearing impairment cannot always be found in children with a failed test.

Objective. Electrically evoked auditory steady-state responses (EASSRs) are potentially useful for objective cochlear implant (CI) fitting and follow-up of the auditory maturation in infants and children with a CI. EASSRs are recorded in the electro-encephalogram (EEG) in response to electrical stimulation with continuous pulse trains, and are distorted by significant CI artifacts related to this electrical stimulation. The aim of this study is to evaluate a CI artifacts attenuation method based on independent component analysis (ICA) for three EASSR datasets. Approach. ICA has often been used to remove CI artifacts from the EEG to record transient auditory responses, such as cortical evoked auditory potentials. Independent components (ICs) corresponding to CI artifacts are then often manually identified. In this study, an ICA based CI artifacts attenuation method was developed and evaluated for EASSR measurements with varying CI artifacts and EASSR characteristics. Artifactual ICs were automatically identified based on their spectrum. Main results. For 40 Hz amplitude modulation (AM) stimulation at comfort level, in high SNR recordings, ICA succeeded in removing CI artifacts from all recording channels, without distorting the EASSR. For lower SNR recordings, with 40 Hz AM stimulation at lower levels, or 90 Hz AM stimulation, ICA either distorted the EASSR or could not remove all CI artifacts in most subjects, except for two of the seven subjects tested with low level 40 Hz AM stimulation. Noise levels were reduced after ICA was applied, and up to 29 ICs were rejected, suggesting poor ICA separation quality. Significance. We hypothesize that ICA is capable of separating CI artifacts and EASSR in case the contralateral hemisphere is EASSR dominated. For small EASSRs or large CI artifact amplitudes, ICA separation quality is insufficient to ensure complete CI artifacts attenuation without EASSR distortion.

Acoustic hearing implants, such as direct acoustic cochlear implants (DACIs), can be used to treat profound mixed hearing loss. Electrophysiological responses in DACI subjects are of interest to confirm auditory processing intra-operatively, and to assist DACI fitting postoperatively. We present two related studies, focusing on DACI artifacts and electrophysiological measurements in DACI subjects, respectively. In the first study we aimed to characterize DACI artifacts, to study the feasibility of measuring frequency-specific electrophysiological responses in DACI subjects. Measurements of DACI artifacts were collected in a cadaveric head to disentangle possible DACI artifact sources and compared to a constructed DACI artifact template. It is shown that for moderate stimulation levels, DACI artifacts are mainly dominated by the artifact from the radio frequency (RF) communication signal, that can be modeled if the RF encoding protocol is known. In a second study, the feasibility of measuring intra-operative responses, without applying the RF artifact models, in DACI subjects is investigated. Auditory steady-state and brainstem responses were measured intra-operatively in three DACI subjects, immediately after implantation, to confirm proper DACI functioning and coupling to the inner ear. Intra-operative responses could be measured in two of the three tested subjects. Absence of intra-operative responses in the third subject can possibly be explained by the hearing loss, attenuation of intra-operative responses, the difference between electrophysiological and behavioral threshold, and a temporary threshold shift due to the DACI surgery. In conclusion, RF artifacts can be modeled, such that electrophysiological responses to frequency-specific stimuli could possibly be measured in DACI subjects, and intra-operative responses in DACI subjects can be obtained.

Objective: Electrically evoked auditory steady-state responses (EASSRs) are neural potentials measured in the electroencephalogram (EEG) in response to periodic pulse trains presented, for example, through a cochlear implant (CI). EASSRs could potentially be used for objective CI fitting. However, EEG signals are contaminated with electrical CI artifacts. In this paper, we characterized the CI artifacts for monopolar mode stimulation and evaluated at which pulse rate, linear interpolation over the signal part contaminated with CI artifact is successful.Methods: CI artifacts were characterized by means of their amplitude growth functions and duration.Results: CI artifact durations were between 0.7 and 1.7 ms, at contralateral recording electrodes. At ipsilateral recording electrodes, CI artifact durations are range from 0.7 to larger than 2 ms.Conclusion: At contralateral recording electrodes, the artifact was shorter than the interpulse interval across subjects for 500 pps, which was not always the case for 900 pps. Significance: CI artifact-free EASSRs are crucial for reliable CI fitting and neuroscience research. The CI artifact has been characterized and linear interpolation allows to remove it at contralateral recording electrodes for stimulation at 500 pps. (C) 2016 The Authors. Published by Elsevier Ltd.

Objectives: Measuring speech intelligibility in quiet and noise is important in clinical practice and research. An easy-to-use free software platform for conducting speech tests is presented, called APEX/SPIN. Design: The APEX/SPIN platform allows the use of any speech material in combination with any noise. A graphical user interface provides control over a large range of parameters, such as number of loudspeakers, signal-to-noise ratio and parameters of the procedure. An easy-to-use graphical interface is provided for calibration and storage of calibration values. To validate the platform, perception of words in quiet and sentences in noise were measured both with APEX/SPIN and with an audiometer and CD player, which is a conventional setup in current clinical practice. Study sample: Five normal-hearing listeners participated in the experimental evaluation. Results: Speech perception results were similar for the APEX/SPIN platform and conventional procedures. Conclusions: APEX/SPIN is a freely available and open source platform that allows the administration of all kinds of custom speech perception tests and procedures.

Previous studies have shown that objective measures based on stimulation with low-rate pulse trains fail to predict the threshold levels of cochlear implant (CI) users for high-rate pulse trains, as used in clinical devices. Electrically evoked auditory steady-state responses (EASSRs) can be elicited by modulated high rate pulse trains, and can potentially be used to objectively determine threshold levels of CI users. The responsiveness of the auditory pathway of profoundly hearing-impaired CI users to modulation frequencies is, however, not known. In the present study we investigated the responsiveness of the auditory pathway of CI users to a monopolar 500 pulses per second (pps) pulse train modulated between 1 and 100 Hz. EASSRs to forty-three modulation frequencies, elicited at the subject's maximum comfort level, were recorded by means of electroencephalography. Stimulation artifacts were removed by a linear interpolation between a pre- and post-stimulus sample (i.e., blanking). The phase delay across modulation frequencies was used to differentiate between the neural response and a possible residual stimulation artifact after blanking. Stimulation artifacts were longer than the inter-pulse interval of the 500 pps pulse train for recording electrodes ipsilateral to the Cl. As a result the stimulation artifacts could not be removed by artifact removal on the bases of linear interpolation for recording electrodes ipsilateral to the Cl. However, artifact-free responses could be obtained in all subjects from recording electrodes contralateral to the CI, when subject specific reference electrodes (Cz or Fpz) were used. EASSRs to modulation frequencies within the 30-50 Hz range resulted in significant responses in all subjects. Only a small number of significant responses could be obtained, during a measurement period of 5 min, that originate from the brain stem (i.e., modulation frequencies in the 80-100 Hz range). This reduced synchronized activity of brain stem responses in long-term severely-hearing impaired CI users could be an attribute of processes associated with long-term hearing impairment and/or electrical stimulation. (C) 2016 Elsevier B.V. All rights reserved.

Cochlear implant (CI) stimulation artifacts are currently removed from electrically evoked steady-state response (EASSR) measurements based on a linear interpolation (LI) over the artifact-contaminated signal parts. LI is only successful if CI stimulation artifacts are shorter than the interpulse interval, i.e., for contralateral channels and stimulation pulse rates up to 500 pulses per second (pps). The objective of this paper is to develop and evaluate a template subtraction (TS) method to remove continuous CI stimulation artifacts in order to accurately measure EASSRs. The template construction (TC) is based on an EEG recording containing CI stimulation artifacts but no synchronous neural response. The constructed templates are subtracted from the recording of interest. Response amplitudes and latencies are compared for the TS and LI method, and for different TC durations. The response amplitudes and latencies in contralateral channels are the same after TS and LI, as expected. In ipsilateral channels, response amplitudes and latencies are within the expected range only after TS. The TC duration can be reduced from 5 min to 1 min without a significant effect on response latency. TS with a TC duration of only 1 min allows to remove all CI stimulation artifacts in individual contra- and ipsilateral EEG recording channels.

OBJECTIVES:Direct acoustic cochlear implants directly stimulate the cochlear fluid of the inner ear by means of a stapes piston driven by an actuator and show encouraging speech understanding in noise results for patients with severe to profound mixed hearing loss. Auditory evoked potentials recorded in such patients would allow for the objective evaluation of the aided auditory pathway. The aim of this study was (1) to develop a stimulation setup for EEG recordings in subjects with direct acoustic cochlear implants, (2) to show the feasibility of recording auditory brainstem responses (ABRs) and auditory steady state responses (ASSRs), and (3) to analyze the relation between electrophysiological thresholds derived from these responses and behavioral thresholds.DESIGN:For the three subjects implanted during a phase Ib clinical study in the authors' center, ABRs and 40 and 80 Hz ASSRs were recorded with a straightforward acoustic stimulation setup and a newly developed direct stimulation setup. Click trains with rates around 40 Hz and around 90 Hz were used as stimuli. By comparing amplitude growth function and phase delay in the same stimulus range, validity of the responses was confirmed.RESULTS:With the acoustic stimulation setup, stimulation artifacts made it impossible to analyze responses. With the direct stimulation setup, stimulation artifacts could be removed completely and responses could be successfully recorded in a noninvasive manner in all subjects. Response properties such as ABR peak V latencies and ASSR apparent latencies were similar to those for acoustic stimulation, with apparent latencies of 39.9 and 24.7 msec for 40 and 90 Hz, respectively. Electrophysiological thresholds could be objectively determined from the ABRs and ASSRs. In the 40 Hz range, the mean difference between electrophysiological ASSR thresholds and behavioral ones was 12 dB.CONCLUSION:The results show that auditory evoked potential measurements with the developed direct stimulation setup are feasible and meaningful and should be further investigated to provide intraoperative feedback about the coupling of the actuator to the inner ear.

Temporal cues are important for cochlear implant (CI) users when listening to speech. Users with greater sensitivity to temporal modulations show better speech recognition and modifications to stimulation parameters based on modulation sensitivity have resulted in improved speech understanding. Behavioural measures of temporal sensitivity require cooperative participants and a large amount of time. These limitations have motivated the desire for an objective measure with which to appraise temporal sensitivity for Cl users.Electrically evoked auditory steady state responses (EASSRs) are neural responses to periodic electrical stimulation that have been used to predict threshold (T) levels. In this study we evaluate the use of EASSRs as a tool for assessing temporal modulation sensitivity.Modulation sensitivity was assessed behaviourally using modulation detection thresholds (MDTs) for a 20 Hz rate. On the same stimulation sites, EASSRS were measured using sinusoidally amplitude modulated pulse trains at 4 and 40 Hz. Measurements were taken using a bipolar configuration on 12 electrode pairs over 5 participants. Results showed that EASSR amplitudes and signal-to-noise ratios (SNRs) were significantly related to the MDTs. Larger EASSRs corresponded with sites of improved modulation sensitivity. This relation was driven by across-subject variation. This result indicates that EASSRs may be used as an objective measure of site-specific temporal sensitivity for CI users. (C) 2015 The Authors. Published by Elsevier B.V.

In the brain, the temporal analysis of many important auditory features relies on the synchronized firing of neurons to the auditory input rhythm. These so-called neural oscillations play a crucial role in sensory and cognitive processing and deviances in oscillatory activity have shown to be associated with neurodevelopmental disorders. Given the importance of neural auditory oscillations in normal and impaired sensory and cognitive functioning, there has been growing interest in their developmental trajectory from early childhood on. In the present study, neural auditory processing was investigated in typically developing young children (n = 40) and adults (n = 27). In all participants, auditory evoked theta, beta and gamma responses were recorded. The results of this study show maturational differences between children and adults in neural auditory processing at cortical as well as at brainstem level. Neural background noise at cortical level was shown to be higher in children compared to adults. In addition, higher theta response amplitudes were measured in children compared to adults. For beta and gamma rate modulations, different processing asymmetry patterns were observed between both age groups. The mean response phase was also shown to differ significantly between children and adults for all rates. Results suggest that cortical auditory processing of beta develops from a general processing pattern into a more specialized asymmetric processing preference over age. Moreover, the results indicate an enhancement of bilateral representation of monaural sound input at brainstem with age. A dissimilar efficiency of auditory signal transmission from brainstem to cortex along the auditory pathway between children and adults is suggested. These developmental differences might be due to both functional experience-dependent as well as anatomical changes. The findings of the present study offer important information about maturational differences between children and adults for responses to theta, beta and gamma rates. The current study can have important implications for the understanding of developmental disorders which are known to be associated with deviances in neural auditory processing.

BACKGROUND:Missing data within the comprehensive geriatric assessment of the interRAI suite of assessment instruments potentially imply the under-detection of conditions that require care as well as the risk of biased statistical results. Impaired oral health in older individuals has to be registered accurately as it causes pain and discomfort and is related to the general health status.OBJECTIVE:This study was based on interRAI-Home Care (HC) baseline data from 7590 subjects (mean age 81.2 years, SD 6.9) in Belgium. It was investigated if missingness of the oral health-related items was associated with selected variables of general health. It was also determined if multiple imputation of missing data affected the associations between oral and general health.MATERIALS AND METHODS:Multivariable logistic regression was used to determine if the prevalence of missingness in the oral health-related variables was associated with activities of daily life (ADLH), cognitive performance (CPS2) and depression (DRS). Associations between oral health and ADLH, CPS2 and DRS were determined, with missing data treated by 1. the complete-case technique and 2. by multiple imputation, and results were compared.RESULTS:The individual oral health-related variables had a similar proportion of missing values, ranging from 16.3% to 17.2%. The prevalence of missing data in all oral health-related variables was significantly associated with symptoms of depression (dental prosthesis use OR 1.66, CI 1.41-1.95; damaged teeth OR 1.74, CI 1.48-2.04; chewing problems OR 1.74, CI 1.47-2.05; dry mouth OR 1.65, CI 1.40-1.94). Missingness in damaged teeth (OR 1.27, CI 1.08-1.48), chewing problems (OR 1.22, CI 1.04-1.44) and dry mouth (OR 1.23, CI 1.05-1.44) occurred more frequently in cognitively impaired subjects. ADLH was not associated with the prevalence of missing data. When comparing the complete-case technique with the multiple imputation approach, nearly identical odds ratios characterized the associations between oral and general health.CONCLUSION:Cognitively impaired and depressive individuals had a higher risk of missing oral health-related information. Associations between oral health and ADLH, CPS2 and DRS were not influenced by multiple imputation of missing data. Further research should concentrate on the mechanisms that mediate the occurrence of missingness to develop preventative strategies.

Electrically evoked auditory steady state responses (EASSRs) are EEG signals measured in response to periodic or modulated pulse trains presented through a cochlear implant (CI). EASSRs are studied for the objective fitting of CIs in infants, as electrophysiological thresholds determined with EASSRs correlate well with behavioural thresholds. Currently available techniques to remove CI artifacts from such measurements are only able to deal with artifacts for low-rate pulse trains or modulated pulse trains presented in bipolar mode, which are not used in main clinical practice. In this paper, an automatic EASSR CI artifact rejection technique based on independent component analysis (ICA) is presented that is suitable for clinical parameters. Artifactual independent components are selected based on the spectral amplitude of the pulse rate. Electrophysiological thresholds determined based on ICA compensated signals are equal to those detected using blanked signals, but measurements at only one modulation frequency are required.