Continuous Loop Averaging Deconvolution Research Articles

Improved Transient Response Estimations in Predicting 40 Hz Auditory Steady-State Response Using Deconvolution Methods.

The auditory steady-state response (ASSR) is one of the main approaches in clinic for health screening and frequency-specific hearing assessment. However, its generation mechanism is still of much controversy. In the present study, the linear superposition hypothesis for the generation of ASSRs was investigated by comparing the relationships between the classical 40 Hz ASSR and three synthetic ASSRs obtained from three different templates for transient auditory evoked potential (AEP). These three AEPs are the traditional AEP at 5 Hz and two 40 Hz AEPs derived from two deconvolution algorithms using stimulus sequences, i.e., continuous loop averaging deconvolution (CLAD) and multi-rate steady-state average deconvolution (MSAD). CLAD requires irregular inter-stimulus intervals (ISIs) in the sequence while MSAD uses the same ISIs but evenly-spaced stimulus sequences which mimics the classical 40 Hz ASSR. It has been reported that these reconstructed templates show similar patterns but significant difference in morphology and distinct frequency characteristics in synthetic ASSRs. The prediction accuracies of ASSR using these templates show significant differences (p < 0.05) in 45.95, 36.28, and 10.84% of total time points within four cycles of ASSR for the traditional, CLAD, and MSAD templates, respectively, as compared with the classical 40 Hz ASSR, and the ASSR synthesized from the MSAD transient AEP suggests the best similarity. And such a similarity is also demonstrated at individuals only in MSAD showing no statistically significant difference (Hotelling's T2 test, T2 = 6.96, F = 0.80, p = 0.592) as compared with the classical 40 Hz ASSR. The present results indicate that both stimulation rate and sequencing factor (ISI variation) affect transient AEP reconstructions from steady-state stimulation protocols. Furthermore, both auditory brainstem response (ABR) and middle latency response (MLR) are observed in contributing to the composition of ASSR but with variable weights in three templates. The significantly improved prediction accuracy of ASSR achieved by MSAD strongly supports the linear superposition mechanism of ASSR if an accurate template of transient AEPs can be reconstructed. The capacity in obtaining both ASSR and its underlying transient components accurately and simultaneously has the potential to contribute significantly to diagnosis of patients with neuropsychiatric disorders.

Human Summating Potential Using Continuous Loop Averaging Deconvolution: Response Amplitudes Vary with Tone Burst Repetition Rate and Duration.

Electrocochleography (ECochG) to high repetition rate tone bursts may have advantages over ECochG to clicks with standard slow rates. Tone burst stimuli presented at a high repetition rate may enhance summating potential (SP) measurements by reducing neural contributions resulting from neural adaptation to high stimulus repetition rates. To allow for the analysis of the complex ECochG responses to high rates, we deconvolved responses using the Continuous Loop Averaging Deconvolution (CLAD) technique. We examined the effect of high stimulus repetition rate and stimulus duration on SP amplitude measurements made with extratympanic ECochG to tone bursts in 20 adult females with normal hearing. We used 500 and 2,000 Hz tone bursts of various stimulus durations (12, 6, 3 ms) and repetition rates (five rates ranging from 7.1 to 234.38/s). A within-subject repeated measures (rate x duration) analysis of variance was conducted. We found that, for both 500 and 2,000 Hz stimuli, the mean deconvolved SP amplitudes were larger at faster repetition rates (58.59 and 97.66/s) compared to slower repetition rates (7.1 and 19.53/s), and larger at shorter stimulus duration compared longer stimulus duration. Our concluding hypothesis is that large SP amplitude to short duration stimuli may originate primarily from neural excitation, and large SP amplitudes to long duration, fast repetition rate stimuli may originate from hair cell responses. While the hair cell or neural origins of the SP to various stimulus parameters remains to be validated, our results nevertheless provide normative data as a step toward applying the CLAD technique to understanding diseased ears.

New metric for optimizing Continuous Loop Averaging Deconvolution (CLAD) sequences under the 1/f noise model.

Continuous loop averaging deconvolution (CLAD) is one of the proven methods for recovering transient auditory evoked potentials (AEPs) in rapid stimulation paradigms, which requires an elaborated stimulus sequence design to attenuate impacts from noise in data. The present study aimed to develop a new metric in gauging a CLAD sequence in terms of noise gain factor (NGF), which has been proposed previously but with less effectiveness in the presence of pink (1/f) noise. We derived the new metric by explicitly introducing the 1/f model into the proposed time-continuous sequence. We selected several representative CLAD sequences to test their noise property on typical EEG recordings, as well as on five real CLAD electroencephalogram (EEG) recordings to retrieve the middle latency responses. We also demonstrated the merit of the new metric in generating and quantifying optimized sequences using a classic genetic algorithm. The new metric shows evident improvements in measuring actual noise gains at different frequencies, and better performance than the original NGF in various aspects. The new metric is a generalized NGF measurement that can better quantify the performance of a CLAD sequence, and provide a more efficient mean of generating CLAD sequences via the incorporation with optimization algorithms. The present study can facilitate the specific application of CLAD paradigm with desired sequences in the clinic.

Fast Click Rate Electrocochleography and Auditory Brainstem Response in Normal-Hearing Adults Using Continuous Loop Averaging Deconvolution.

Using the continuous loop averaging deconvolution (CLAD) technique for conventional electrocochleography (ECochG) and auditory brainstem response (ABR) recordings, the effects of testing at high stimulus rates may have the potential to diagnose disorders of the inner ear and auditory nerve. First, a body of normative data using the CLAD technique must be established. Extratympanic click ECochG and ABR to seven stimulus rates using CLAD were measured simultaneously from a tympanic membrane electrode and surface electrodes on the forehead and mastoid of 42 healthy individuals. Results showed that the compound action potential (AP) of the ECochG and waves I, III, and V of the ABR decreased in amplitude and increased in latency as stimulus rate was increased from standard 7.1 clicks/s up to 507.81 clicks/s, with sharp reduction in AP amplitude at 97.66 clicks/s and reaching asymptote at 292.97 clicks/s. The summating potential (SP) of the ECochG, however, stayed relatively stable, resulting in increased SP/AP ratios with increasing rate. The SP/AP amplitude ratio showed more stability than AP amplitude findings, thus it is recommended for use in evaluation of cochlear and neural response. Results of both amplitude and latency data from this normative neural adaptation function of the auditory pathway serves as guide for improving diagnostic utility of both ECochG and ABR using CLAD as a reliable technique in distinguishing inner ear and auditory nerve disorders.

Simultaneous acquisition of high-rate early, middle, and late auditory evoked potentials.

Auditory evoked potentials (AEPs) are typically acquired at rates that facilitate their study as segregated by epochs relative to stimulus onset: early (ABR, 1.5-15 ms), middle (MLR, 15-60 ms), and late (LAEP, ≥60 ms) potentials. In particular, late AEPs are often acquired with stimulus repetition rates between 0.1 Hz and 1 Hz, and are bandpass filtered to contain information only within 1-30 Hz. These low repetition rates, filtering and low SNRs eliminate much of the potential contributions of the early and middle-latency responses in AEP recordings. This study aims to demonstrate a method for acquiring whole-AEP responses at higher stimulus repetition rates of 0.5 Hz to 10 Hz, by utilizing the Continuous Loop Averaging Deconvolution (CLAD) method, increasing the bandwidth of the recordings to 1-300 Hz to include early components, and using short-duration chirps to increase synchronous firing of the cochlear and auditory pathway neurons. Such a method may facilitate diagnostic or functional assessment of single AEP recordings for detection, identification, or evaluation of early, middle and late components of auditory responses.

Auditory steady-state responses to 40-Hz click trains: Relationship to middle latency, gamma band and beta band responses studied with deconvolution

The nature of the auditory steady-state responses (ASSR) evoked with 40-Hz click trains and their relationship to auditory brainstem and middle latency responses (ABR/MLR), gamma band responses (GBR) and beta band responses (BBR) were investigated using superposition theory. Transient responses obtained by continuous loop averaging deconvolution (CLAD) and last click responses (LCR) were used to synthesize ASSRs and GBRs. ASSRs were obtained with trains of low jittered 40 Hz clicks presented monaurally and deconvolved using a modified CLAD. Resulting transient responses and modified LCRs were used to predict the ASSRs and the GBR. The ABR/MLR obtained with deconvolution predicted accurately the steady portion of the ASSR but failed to predict its onset portion. The modified LCR failed to fully predict both portions. The GBRs were predicted by narrow band filtering of the ASSRs. Significant BBR activity was found both in the ASSRs and deconvolved ABR/MLRs. Simulations using deconvolved ABR/MLRs obtained at 40 Hz predict fully the steady state but not the onset portion of the ASSRs, thus confirming the superposition theory. Click rate adaptation plays a significant role in ASSR generation with click trains and should be considered in evaluating convolved response generation theories.

Generation of the 40-Hz auditory steady-state response (ASSR) explained using convolution

Objective In this study, the superposition theory of the 40-Hz auditory steady-state response (ASSR) generation is investigated using auditory brainstem response (ABR) and middle latency responses (MLRs) obtained with 40 Hz jittered sequences with the continuous loop averaging deconvolution (CLAD) algorithm. Methods Click sequences at around 40 Hz with high (maximum length sequence), medium and low jitters were presented to normal hearing awake adult subjects monaurally. Overlapping MLR responses were deconvolved using the frequency domain CLAD method. In addition, conventional auditory MLRs at 4.88 Hz and ASSRs at 39.1 Hz were obtained in all subjects. Synthetic ASSRs were constructed using different rate and jitter MLRs as base recordings. Contributions of the primary components were investigated by wave elimination using phasors. Results Findings indicate that the generation of the 40-Hz ASSRs can be explained successfully by the superposition of the ABR and MLR waves generated at that stimulation rate. N a–P a and N b–P b components of the MLR contribute about equally (45% each), while the wave V of the ABR contributes a lesser amount (10%). Conclusions Forty-Hertz ASSRs are composite responses generated by the superposition of the major waves of the ABR and the MLR. Dramatic amplitude increase of the ASSR at 40 Hz is primarily due to the superposition of the resonating P b component to the P a wave. Significance Several unexplained properties of the 40-Hz ASSR can be explained by the stimulus and brain state dependent characteristics of the slow ABR, the P a and the P b components of the MLR.

Suppression of the Pb (P1) component of the auditory middle latency response with contralateral masking

ObjectiveIn this study, the effects of contralateral noise or speech on middle latency response (MLR) components Pa and Pb (P1 or P50) were studied using high rates clicks in normal hearing awake adult subjects. MethodsOne standard (4.88Hz) and four jittered click sequences (24.4, 39.1, 58.6, 78.1Hz) at different mean rates were monaurally presented to ten subjects. The contralateral ears were stimulated with continuous pink noise, recorded speech or no stimulus for control. Overlapping MLR responses to jittered click stimuli were deconvolved using the frequency domain continuous loop averaging deconvolution (CLAD). ResultsThe recordings show that contralateral noise or speech stimulation suppresses Pb component greatly at rates around 40Hz while earlier components (ABR and Pa) are not significantly affected. The suppression of the Pb component is about 50% with some latency reduction. ConclusionsThe results show that the Pb component of the MLR is significantly affected by contralateral stimulus at resonance rates at around 40Hz. It appears that the contralateral noise obliterates the amplitude enlargement due to resonance effect. SignificanceThese findings show that the Pb is generated very differently from the Pa component and strongly inhibited by the contralateral ear. These results also explain the previously observed masking of the 40Hz auditory steady-state responses (ASSR) with contralateral noise.

P b(P 1) resonance at 40 Hz: Effects of high stimulus rate on auditory middle latency responses (MLRs) explored using deconvolution

Objective In this study, the effects of high stimulus rate on middle latency response (MLR) components P a and P b (P 1 or P50) were studied using high rate clicks in normal hearing awake subjects were investigated. Methods Five jittered click sequences at different mean rates (24.4, 39.1, 58.6, 78.1, 97.7 Hz) were presented to 10 subjects. Overlapping MLRs were deconvolved using the frequency domain continuous loop averaging deconvolution (CLAD) [Özdamar Ö., Bohórquez, J., Signal to noise ratio and frequency analysis of continuous loop averaging deconvolution (CLAD) of overlapping evoked potentials. J. Acoust. Soc. Am., 119:429–438, 2006]. In addition conventional auditory transient MLRs at 4.88 Hz were obtained using conventional averaging. Results P a amplitude, latency and waveshape remained fairly constant up to 78.1 Hz. P b component, however, showed a variable waveshape with latencies covering a wide range (50–70 ms) and N b–P b amplitudes increasing at 39.1 and 58.6 Hz and decreasing at other rates. Conclusions Recordings show that both P a and P b MLR components can be consistently recorded at all rates up to 100 Hz. P b amplitude shows an increase at around 40 Hz showing a resonance at that frequency. Significance The dramatic increase of the P b component at around 40 Hz may account for the high amplitude of the 40 Hz ASSR.

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 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.

Deconvolution of evoked responses obtained at high stimulus rates.

Continuous loop averaging deconvolution (CLAD) is a new general mathematical theory and method developed to deconvolve overlapping auditory evoked responses obtained at high stimulation rates. Using CLAD, arbitrary stimulus sequences are generated and averaged responses deconvolved. Until now, only a few special stimulus series such as maximum length sequences (MLS) and Legendre sequences (LGS) were capable of performing this task. A CLAD computer algorithm is developed and implemented in an evoked potential averaging system. Computer simulations are used to verify the theory and methodology. Auditory brainstem responses (ABR) and middle latency responses (MLR) are acquired from subjects with normal hearing at high stimulation rates to validate and show the feasibility of the CLAD technique.