Effects of stimulus rate on the feline brain-stem auditory evoked response during development. II. Peak amplitudes

Examining the Profile of Noise-Induced Cochlear Synaptopathy Using iPhone Health App Data and Cochlear and Brainstem Electrophysiological Responses to Fast Clicks Rates

Little is known about objective classifying of noise exposure risk levels in personal listening device (PLD) users and electrophysiologic evidence of cochlear synaptopathy at very fast click rates. The aim of the study was to objectively classify noise exposure risk using iPhone Health app and identify signs of cochlear synaptopathy using behavioral and electrophysiologic measures. Thirty normal-hearing females (aged 18-26 years) were grouped based on their iPhone Health app's 6-month listening level and noise exposure data into low-risk and high-risk groups. They were assessed using a questionnaire, extended high-frequency (EHF) audiometry, QuickSIN test, distortion-product otoacoustic emission (DPOAE), and simultaneous recording of electrocochleography (ECochG) and auditory brainstem response (ABR) at three click rates (19.5/s, 97.7/s, 234.4/s). A series of ANOVAs and independent samples t -test were conducted for group comparison. Both groups had within-normal EHF hearing thresholds and DPOAEs. However, the high-risk participants were over twice as likely to suffer from tinnitus, had abnormally large summating potential to action potential amplitude and area ratios at fast rates, and had slightly smaller waves I and V amplitudes. The high-risk group demonstrated a profile of behavioral and objective signs of cochlear synaptopathy based on ECochG and ABR recordings at fast click rates. The findings in this study suggest that the iPhone Health app may be a useful tool for further investigation into cochlear synaptopathy in PLD users.

Signal-to-noise ratio of auditory brainstem responses (ABRs) across click rate in the bottlenose dolphin (Tursiops truncatus)

Although the maximum length sequence (MLS) and iterative randomized stimulation and averaging (I-RSA) methods allow auditory brainstem response (ABR) measurements at high rates, it is not clear if high rates allow ABRs of a given quality to be measured in less time than conventional (CONV) averaging (i.e., fixed interstimulus intervals) at lower rates. In the present study, ABR signal-to-noise ratio (SNR) was examined in six bottlenose dolphins as a function of measurement time and click rate using CONV averaging at rates of 25 and 100 Hz and the MLS/I-RSA approaches at rates from 100 to 1250 Hz. Residual noise in the averaged ABR was estimated using (1) waveform amplitude following the ABR, (2) waveform amplitude after subtracting two subaverage ABRs (i.e., the "±average"), and (3) amplitude variance at a single time point. Results showed that high stimulus rates can be used to obtain dolphin ABRs with a desired SNR in less time than CONV averaging. Optimal SNRs occurred at rates of 500-750 Hz, but were only a few dB higher than that for CONV averaging at 100 Hz. Nonetheless, a 1-dB improvement in SNR could result in a 25% time savings in reaching criterion SNR.

Comparison of maximum length sequence and randomized stimulation and averaging methods on the bottlenose dolphin auditory brainstem response

The purpose of the present study was to compare auditory brainstem responses (ABRs) using two approaches that allow the use of high stimulation rates, but with different temporal variability in the interstimulus interval: maximum length sequences (MLS) and iterative randomized stimulation and averaging (I-RSA). ABRs were obtained to click stimuli in six bottlenose dolphins (Tursiops truncatus). In experiment 1, click level was held constant and click rate varied from 25 to 1250 Hz. For MLS, interstimulus intervals varied by a factor of 6 at each rate, while for I-RSA the interstimulus intervals varied by ± 0.5 ms regardless of rate. In experiment 2, stimulus rates ranged from 100 to 1000 Hz and click level varied from 105 to 135 dB re: 1 μPa. For experiment 1, MLS and I-RSA showed similar decreases in ABR peak amplitudes and increases in ABR peak latencies and interwave intervals with increasing rate. For experiment 2, there was an increase in peak latency and a decrease in peak amplitude with decreasing click level; however, the effects of click level were reduced at higher rates. The results indicate that the greater jitter for MLS compared to I-RSA does not substantially affect the dolphin ABR.

Bottlenose dolphin (Tursiops truncatus) auditory brainstem responses recorded using conventional and randomized stimulation and averaging

Auditory brainstem response (ABR) measurements using conventional averaging (i.e., constant interstimulus interval, ISI) are limited to stimulus rates low enough to prevent overlapping of the ABRs to successive stimuli. To overcome this limitation, stimuli may be presented at high rates using pseudorandom sequences (e.g., maximum length sequences) or quasi-periodic sequences; however, these methods restrict the available stimulus sequences and require deconvolution to recover the ABR from the overlapping responses. Randomized stimulation and averaging (RSA) is an alternate method where evoked responses at high rates are obtained by averaging responses to stimuli with ISIs drawn from a random distribution. The RSA method enables precise control over stimulus jitter, is flexible with respect to stimulus sequence parameters, and does not require deconvolution to extract the ABR waveform. In this study, ABRs were measured in three normal-hearing dolphins using conventional averaging and RSA. Results show the RSA method to be effective in dolphins if the ISI jitter ≥ ∼1.5 ms and that the influence of stimulus artifacts in the averaged ABR can be substantially reduced by alternating stimulus polarity on successive presentations rather than employing digital blanking or iterative processes.

The effects of click rate on the auditory brainstem response of bottlenose dolphins

Rate manipulations can be used to study adaptation processes in the auditory nerve and brainstem. For this reason, rate effects on the click-evoked auditory brainstem response (ABR) have been investigated in many mammals, including humans. In this study, click-evoked ABRs were obtained in eight bottlenose dolphins (Tursiops truncatus) while varying stimulus rate using both conventional averaging and maximum length sequences (MLSs), which allow disentangling ABRs that overlap in time and thus permit the study of adaptation at high rates. Dolphins varied in age and upper cutoff frequency of hearing. Conventional stimulation rates were 25, 50, and 100 Hz and average MLS rates were approximately 50, 100, 250, 500, 1000, 2500, and 5000 Hz. Click peak-equivalent sound pressure levels for all conditions were 135 dB re 1 μPa. ABRs were observed in all dolphins, at all stimulus rates. With increasing rate, peak latencies increased and peak amplitudes decreased. There was a trend for an increase in the interwave intervals with increasing rate, which appeared more robust for the dolphins with a full range of hearing. For those rates where ABRs were obtained for both conventional and MLS approaches, the latencies of the mean data were in good agreement.

Baseline correction of overlapping event-related responses using a linear deconvolution technique

The time it takes an event-related response (ERR) to subside is often longer than the interval between successive events so that the response to a new event interferes with a baseline formed by responses to preceding events. Thus, without proper baseline correction, the interpretation of an event-triggered average (ETA) of recorded data can be problematic. As the spectral compositions of ERR and baseline typically overlap, filtering the ETA is not always an adequate solution. The approach introduced here exploits that ETA and ERR are linearly related. Unless the series of events is exactly periodic, the ERR can be derived from the ETA by linear deconvolution. The performance of the method is illustrated with simulated examples as well as data from an auditory evoked field (AEF) study. It is also outlined how to handle experiments with two or more different events. Intriguing applications beyond the scope of baseline correction arise from the fact that the ERR is invariably estimated for a time window longer than the mean interval between successive events. The method may help, for example, to better understand the relationship between transient and steady-state responses or to delineate the component structure of a specific ERR.

Wiener filter deconvolution of overlapping evoked potentials

Evoked potentials (EPs) typically contain components that last up to several seconds. In order to save time and study adaptation effects, stimuli are often presented at high stimulation rates. Unfortunately, such protocols often suffer from a response overlap problem. Techniques based on Continuous Loop Averaging Deconvolution (CLAD) have been developed to formulate circular convolution to restore the source EP. These techniques, however, are sensitive to the additive noise and do not perform well when stimulus sequences with poor noise attenuation properties are chosen. This study offers a solution to this problem by applying Wiener theory to obtain an optimal filter that adapts the ratio of noise-to-signal by estimating the power spectra of both noise and signal using non-parametric or parametric methods. Experiments are conducted on simulation data and Auditory Evoked potentials (AEPs) acquired from human subjects to demonstrate the validity of the proposed theory. The results show that the Wiener deconvolution method improves the quality of the responses acquired with sequences with poor noise attenuation in the presence of high noise levels compared to the straight CLAD method. The results are comparable to responses obtained by conventional and Maximum Length Sequence (MLS) methods.

Signal to noise ratio analysis of maximum length sequence deconvolution of overlapping evoked potentials

In this study a general formula for the signal to noise ratio (SNR) of the maximum length sequence (MLS) deconvolution averaging is developed using the frequency domain framework of the generalized continuous loop averaging deconvolution procedure [Ozdamar and Bohórquez, J. Acoust. Soc. Am. 119, 429-438 (2006)]. This formulation takes advantage of the well known equivalency of energies in the time and frequency domains (Parseval's theorem) to show that in MLS deconvolution, SNR increases with the square root of half of the number of stimuli in the sweep. This increase is less than that of conventional averaging which is the square root of the number of sweeps averaged. Unlike arbitrary stimulus sequences that can attenuate or amplify phase unlocked noise depending on the frequency characteristics, the MLS deconvolution attenuates noise in all frequencies consistently. Furthermore, MLS and its zero-padded variations present optimal attenuation of noise at all frequencies yet they present a highly jittered stimulus sequence. In real recordings of evoked potentials, the time advantage gained by noise attenuation could be lost by the signal amplitude attenuation due to neural adaptation at high stimulus rates.

Signal-to-noise ratio and frequency analysis of continuous loop averaging deconvolution (CLAD) of overlapping evoked potentials

In this study, a frequency domain formulation of continuous loop averaging deconvolution (CLAD) of overlapping evoked potentials is developed and applied for the extraction of transient responses from recordings obtained at high stimulation rates. This formulation allows for a faster execution of CLAD by using fast Fourier transform algorithms. The frequency characteristics of the deconvolution filter depends exclusively on the stimulus sequence and determines whether the noncoherent noise is amplified or attenuated in different frequencies. A formula for calculating the signal-to-noise ratio (SNR) achieved by the deconvolution process is developed. The newly developed theory and the methodology is applied to the extraction of the auditory brainstem and middle latency responses using various sequences. The effects of the sequence used and the number of sweeps averaged in ongoing acquisition on SNR are examined by using single sweep recordings. The results verify the deconvolution theory and the methodology and show its limitations. Depending on the frequency characteristics of the sequence, the deconvolution process can amplify or attenuate the EEG noise. Proper selection of the stimulus sequence can increase the SNR enhancement obtained with conventional averaging.

Auditory brainstem responses in the Eastern Screech Owl: an estimate of auditory thresholds

The auditory brainstem response (ABR), a measure of neural synchrony, was used to estimate auditory sensitivity in the eastern screech owl (Megascops asio). The typical screech owl ABR waveform showed two to three prominent peaks occurring within 5 ms of stimulus onset. As sound pressure levels increased, the ABR peak amplitude increased and latency decreased. With an increasing stimulus presentation rate, ABR peak amplitude decreased and latency increased. Generally, changes in the ABR waveform to stimulus intensity and repetition rate are consistent with the pattern found in several avian families. The ABR audiogram shows that screech owls hear best between 1.5 and 6.4 kHz with the most acute sensitivity between 4-5.7 kHz. The shape of the average screech owl ABR audiogram is similar to the shape of the behaviorally measured audiogram of the barn owl, except at the highest frequencies. Our data also show differences in overall auditory sensitivity between the color morphs of screech owls.

Development of auditory sensitivity in budgerigars (Melopsittacus undulatus)

Auditory feedback influences the development of vocalizations in songbirds and parrots; however, little is known about the development of hearing in these birds. The auditory brainstem response was used to track the development of auditory sensitivity in budgerigars from hatch to 6 weeks of age. Responses were first obtained from 1-week-old at high stimulation levels at frequencies at or below 2 kHz, showing that budgerigars do not hear well at hatch. Over the next week, thresholds improved markedly, and responses were obtained for almost all test frequencies throughout the range of hearing by 14 days. By 3 weeks posthatch, birds' best sensitivity shifted from 2 to 2.86 kHz, and the shape of the auditory brainstem response (ABR) audiogram became similar to that of adult budgerigars. About a week before leaving the nest, ABR audiograms of young budgerigars are very similar to those of adult birds. These data complement what is known about vocal development in budgerigars and show that hearing is fully developed by the time that vocal learning begins.

Functional development of the auditory brainstem in the tammar wallaby (Macropus eugenii): the superior olivary complex and its relationship with the auditory brainstem response (ABR)

Twenty pouch-young tammar wallabies (Macropus eugenii) were used to determine the generator of the auditory brainstem response (ABR) during development through ABR and focal superior olivary complex (SO) recordings. A click response from the SO in the wallaby was recorded from postnatal day (PND) 112 when the ABR was only a positive-negative deflection. Before PND 120, the SO response did not contribute to the ABR as it occurred outside the ABR time-span. After PND 140, the SO response was correlated with multiple waves of the ABR with its dominant component corresponding to the ABR P3 wave. The latency, threshold, and amplitude of the SO response developed to the adult-like level at PND 140, while the rate-following ability in the SO response reached the adult level at PND 160. Presumably this was due to more complicated mechanisms underlying the auditory adaptation. The adaptation of the SO response was directly proportional to the stimulus rate and intensity as well as developmental status. Developmental comparison between the ABR and the focal responses from four auditory brainstem nuclei indicated that each ABR component may have a dominant contributor from the auditory brainstem, but there was no simple and exclusive association between the ABR component and the auditory brainstem nuclei.

Auditory brainstem responses in adult budgerigars (Melopsittacus undulatus)

The auditory brainstem response (ABR) was recorded in adult budgerigars (Melopsittacus undulatus) in response to clicks and tones. The typical budgerigar ABR waveform showed two prominent peaks occurring within 4 ms of the stimulus onset. As sound-pressure levels increased, ABR peak latency decreased, and peak amplitude increased for all waves while interwave interval remained relatively constant. While ABR thresholds were about 30 dB higher than behavioral thresholds, the shape of the budgerigar audiogram derived from the ABR closely paralleled that of the behavioral audiogram. Based on the ABR, budgerigars hear best between 1000 and 5700 Hz with best sensitivity at 2860 Hz-the frequency corresponding to the peak frequency in budgerigar vocalizations. The latency of ABR peaks increased and amplitude decreased with increasing repetition rate. This rate-dependent latency increase is greater for wave 2 as indicated by the latency increase in the interwave interval. Generally, changes in the ABR to stimulation intensity, frequency, and repetition rate are comparable to what has been found in other vertebrates.

A comparison of the effects of broadband masking noise on the auditory brainstem response in young and older adults

We examined the effects of ipsilateral-direct, continuous, broadband noise on auditory brainstem response (ABR) wave I and V latencies and amplitudes in young adult versus older adult humans. It was hypothesized that age might influence the effects of masking noise on ABR peak latencies and/or amplitudes, given the frequent complaint of older persons' ability to process speech in background noise. Young adults had hearing thresholds of 20 dB HL or better for the octave frequencies from 250 to 8,000 Hz. A subset of older study participants had thresholds of 20 dB HL or better across frequency, but others had thresholds up to 45 dB HL. All data were collected and analyzed with a Nicolet Bravo. An electrode was placed on the tympanic membrane (as well as on high forehead and contralateral mastoid), and a click level of 115 dB pSPL was used to maximize wave I amplitude. Masker conditions included a no-noise control and noise levels ranging from 20 to 70 dB effective masking, in 10 dB steps. With increasing noise level, both age groups showed minimal changes in wave I latency, but substantial increases in wave V latency and I-V interval. Peak amplitudes decreased with increasing noise level. Mean amplitudes were smaller for the older group, most notably for wave I. Mean peak latencies were greater in the older group, but the I-V interval was similar across age groups, as was the change in peak latencies and I-V interval across noise level. ABR parameters for the older adults with hearing meeting the 20-dB HL criterion at all frequencies (older-better) were compared to those who didn't meet this criterion (older-worse). Mean wave I latency was greater and wave V latency and I-V interval were smaller for the older-worse group at all noise levels. Mean wave I and V amplitudes were similar for the older-better and older-worse groups. In participants with normal or near-normal hearing, ABR changes with increasing age included small latency increases and a substantial reduction in wave I amplitude. The effects of ipsilateral-direct masking noise on the click-evoked ABR are similar for young and older adults.

The human auditory brainstem response to high click rates: aging effects

In 1999 J. Walton, M. Orlando, & R. Burkard (Hearing Research, 127, 86-94) investigated aging effects on auditory brainstem response (ABR) wave V latency using a tone-on-toneburst forward-masking paradigm. They found that at short forward-masking intervals, wave V latency shift was greater in normal-hearing older adults than in normal-hearing young adults for moderate level, high-frequency toneburst maskers and probes. It was not possible to evaluate wave I latency because stimulation and recording procedures did not produce a consistently observable wave I. In order to optimize the recording of wave I, the present study used a high-level (115 dB pSPL) click stimulus, combined with a tympanic membrane inverting electrode, and investigated the latencies and amplitudes of waves I and V across click rate. Young adults had hearing thresholds within normal limits, whereas older adults had normal hearing or mild threshold elevation. All data were collected and analyzed with a Nicolet Bravo. Using conventional recording procedures, ABRs were obtained at click rates of 11, 25, 50, and 75 Hz. Using maximum length sequences (MLSs), ABRs were obtained at 100, 200, 300, 400, and 500 Hz. Results across age groups were very similar. With increasing click rate, peak latencies increased, the I-V interval increased and peak amplitudes decreased. The most notable difference between age groups was that wave I amplitude was substantially smaller in the older subjects. It appears that changes in the ABR with increasing rate are remarkably similar in young and older adults when audiometric thresholds are normal or near-normal in both age groups.

Near-field responses from the round window, inferior colliculus, and auditory cortex of the unanesthetized chinchilla: manipulations of noiseburst level and rate

Few studies have compared the response properties of near-field potentials from multiple levels of the auditory nervous system of unanesthetized animals. The purpose of this study was to investigate the effects of brief-duration noisebursts on neural responses recorded from electrodes chronically implanted at the round window, inferior colliculus and auditory cortex of chinchillas. Responses were obtained from seven unanesthetized chinchillas to a noiseburst-level and noiseburst-rate series. For the noiseburst-rate series, a 70 dB pSPL noiseburst was varied in rate from 10 to 100 Hz using conventional averaging procedures, and from 100 to 500 Hz using pseudorandom pulse trains called maximum length sequences (MLSs). Response thresholds were similar for the compound action potential (CAP), inferior colliculus potential (ICP) and auditory cortex potential (ACP). With decreasing noiseburst level, there were decreases in the amplitudes and increases in the latencies of the CAP, ICP and ACP. The shapes of the mean normalized amplitude input/output (I/O) functions were similar for the ICP and ACP, while the normalized I/O functions for the first positive peak (P1) and first negative peak (N1) of the CAP differed from each other and from the ICP and ACP. The slopes of the latency/intensity functions were shallowest for the CAP, intermediate for the ICP, and steepest for the ACP. With increasing rate, the latency shift was least for the CAP, intermediate for the ICP and greatest for the ACP. The amplitude of P1 of the CAP varied little with rate. All other potentials showed a pronounced decrease in amplitude at high stimulation rates. Excluding CAP P1, proportional amplitude decrease with rate was greatest for the ACP, intermediate for N1 of the CAP and least for the ICP. Responses were present in most animals at all recording sites, even for the highest rate (500 Hz) used in this study. For all potentials, the MLS procedure allowed the collection of a response at rates well above those where sequential responses would have overlapped using conventional averaging procedures.

The effects of click level, click rate, and level of background masking noise on the inferior colliculus potential (ICP) in the normal and carboplatin-treated chinchilla

Carboplatin produces a selective loss of inner hair cells in chinchilla, substantially reducing the amplitude of the compound action potential. A key question that arises from these experiments is: What effect does a reduction in IHC-eighth-nerve fiber input have on the central auditory nervous system? This investigation evaluated the inferior colliculus potential (ICP) in chinchillas treated with carboplatin. The left ear was surgically destroyed and a recording electrode was placed in the left inferior colliculus. Following thirteen days of recovery time, the ICP was recorded in the awake animal. Click level was varied from 10-20 to 80 dB pSPL. Click rate was varied from 10 to 1000 Hz using both conventional averaging and a cross-correlation procedure. Broadband masking noise was varied from 30 to 70 dB SPL with click level held constant at 80 dB pSPL. The dependent variables were the positive peak latency and peak-to-following trough amplitude of the evoked potential. Following baseline studies, the animals were administered carboplatin (50 mg/kg IP) and retested two weeks later. Prior to carboplatin administration, there was an increase in ICP latency and a decrease in ICP amplitude with decreasing stimulus level, increasing rate and increasing noise level. Mean ICP threshold was 30 dB pSPL. Following carboplatin administration, there was little change in threshold or peak latencies. In contrast, the amplitude of the ICP was reduced on average by one-third, although this effect varied considerably across animals. The magnitude of this amplitude decrement was not strongly dependent on click level, click rate, or the level of background noise.

Rate and adaptation effects on the auditory evoked brainstem response in human newborns and adults

Auditory evoked brainstem response (ABR) latencies increased and amplitudes decreased with increasing stimulus repetition rate for human newborns and adults. The wave V latency increases were larger for newborns than adults. The wave V amplitude decreases were smaller for newborns than adults. These differences could not be explained by developmental differences in frequency responsivity. The transition from the unadapted to the fully adapted response was less rapid in newborns than adults at short (= 10 ms) inter stimulus intervals (ISIs). At longer ISIs (= 20 ms) there were no developmental differences in the transition to the fully adapted response. The newborn transition occurred in a two stage process. The rapid initial stage observed in adults and newborns was complete by about 40 ms. A second slower stage was observed only in newborns although it has been observed in adults in other studies (Weatherby and Hecox, 1982; Lightfoot, 1991; Lasky et al., 1996). These effects were replicated at different stimulus intensities. After the termination of stimulation the return to the wave V unadapted response took nearly 500 ms in newborns. Neither the newborn nor the adult data can be explained by forward masking of one click on the next click. These results indicate human developmental differences in adaptation to repetitive auditory stimulation at the level of the brainstem.

Responses of chopper units in the ventral cochlear nucleus of the anaesthetised guinea pig to clicks-in-noise and click trains

Auditory brainstem responses (ABRs) have been measured with clicks, clicks masked by noise, click trains and pseudorandom maximum length sequences (MLS) of clicks. To investigate the neuronal populations contributing to the ABR under these stimulation conditions, we measured the extracellular responses of ventral cochlear nucleus (VCN) units in the urethane-anaesthetised guinea pig. We studied 23 chopper, 7 primary-like and 7 onset units. This report focuses on the responses from chopper units. The probability of discharge for chopper units increased with increasing click level reaching nearly 100% in many units, over a range of about 20-30 dB. Following each response to a click there was a 5-10 ms suppression of the spontaneous or noise evoked activity. As the level of the noise was increased over a range of 20-30 dB, the response to the clicks gradually decreased leading to a complete abolition of the click response at high noise levels. In a few units, low level noise produced a facilitation of the response to single clicks. In response to constant level equally spaced click trains, discharge probability increased with increasing minimum pulse interval (MPI), approaching 100% for MPIs of 4-8 ms in some units. The recovery afforded by the gaps in the MLS train often resulted in higher discharge probability for MLS than click trains with the same MPI, while response probabilities for MLS and click trains were similar when compared at equivalent average click rates. At short MPIs (0.5 and 1.0 ms), peri stimulus time histograms in response to click trains resembled those to best frequency (BF) tones and noisebursts, with chopping peaks unrelated to unit BF. VCN units show highly synchronised and reliable responses to click trains, MLS trains and clicks masked by noise. The decrease in discharge rate and increase in latency of chopper units with decreasing click level, increasing click rate and increasing masker level parallel the peak amplitude and latency changes observed in the auditory brainstem response.