Effects of stimulus level on cortical auditory event-related potentials evoked by speech

The effect of stimulus level on cortical auditory event-related potentials (ERPs) evoked by consonant-vowel (CV) contrasts, /ta/, /da/, and /sa/, was investigated. The lowest level at which CVs were discriminated with >95% accuracy was determined for 15 normally hearing adults. ERPs were obtained at 0, 20, and 40 dB SL above this level during active listening. ERP latencies decreased as level increased. P300 amplitude did not vary with CV level or type; however, obligatory ERPs decreased in amplitude as level increased. The effect of level on P300 latency is likely related to the cognitive processing speed needed to perform speech discrimination. Obligatory ERP amplitude results suggest that attention demands vary with level during discrimination of speech features.     

Effects of hearing aid amplification and stimulus intensity on cortical auditory evoked potentials

Hearing aid amplification can be used as a model for studying the effects of auditory stimulation on the central auditory system (CAS). We examined the effects of stimulus presentation level on the physiological detection of sound in unaided and aided conditions. P1, N1, P2, and N2 cortical evoked potentials were recorded in sound field from 13 normal-hearing young adults in response to a 1000-Hz tone presented at seven stimulus intensity levels. As expected, peak amplitudes increased and peak latencies decreased with increasing intensity for unaided and aided conditions. However, there was no significant effect of amplification on latencies or amplitudes. Taken together, these results demonstrate that 20 dB of hearing aid gain affects neural responses differently than 20 dB of stimulus intensity change. Hearing aid signal processing is discussed as a possible contributor to these results. This study demonstrates (1) the importance of controlling for stimulus intensity when evoking responses in aided conditions, and (2) the need to better understand the interaction between the hearing aid and the CAS.     

Habituation and rate effect in the auditory cortical potentials evoked by trains of stimuli

Summary The effects of the stimulus repetition rate over the habituated auditory cortical evoked responses were studied. The stimulation pattern consisted of trains of pure tone bursts with interstimulus interval (ISI) of 1 s, and intertrain interval (ITI) of 5 s, delivered with constant time and intensity parameters during 93 min. The analysis of the responses was based upon across averaging of the trains, each single response being evaluated in the latency and amplitude parameters. Two time-dependent factors affected the responses in a distinct way: the habituation throughout the whole stimulation and the rate effect within the train. The linear regressions of the time/amplitude functions of the responses were calculated in relation to the duration of ISI and ITI. By introducing a correction factor depending on the repetition rate it was possible to evaluate the relationships between habituation and repetition rate. Changes in the repetition rate do not have any effect on the habituation process. The two phenomena are completely distinct, and they probably have neurophysiologic substrates corresponding to different levels in the central nervous system (CNS).     

Brainstem auditory evoked potentials with increased stimulus rate in patients suffering from systemic lupus erythematosus

Central nervous system involvement in systemic lupus erythematosus is frequently occult, may be the presenting sign, and is a bad prognostic indicator. At present, there is no reliable, sensitive laboratory test for the evaluation and diagnosis of subclinical central nervous system involvement of the disease. Brainstem auditory evoked potentials with and without increased stimulus rate have been used to diagnose ischemic lesions in the central nervous system. Brainstem auditory evoked potentials, with and without increased stimulus rate, was used to investigate 15 systemic lupus erythematosus patients, 20 normal participants, and 5 patients receiving corticosteroids for bronchial asthma. A significant statistical difference was found in the net effect of increased stimulus rate in comparisons of the systemic lupus erythematosus patients with the normal group. Brainstem auditory evoked potentials, with increased stimulus rate, demonstrated subclinical involvement of the central nervous system in systemic lupus erythematosus, reinforcing the notion that increased stimulus rate measures are sensitive to ischemic changes, in this case, even in neurologically asymptomatic patients.     

Speech evoked potentials: from the laboratory to the clinic

Speech-evoked auditory event-related potentials (ERPs) provide insight into the neural mechanisms underlying speech processing. For this reason, ERPs are of great value to hearing scientists and audiologists. This article will provide an overview of ERPs frequently used to examine the processing of speech and other sound stimuli. These ERPs include the P1-N1-P2 complex, acoustic change complex, mismatch negativity, and P3 responses. In addition, we focus on the application of these speech-evoked potentials for the assessment of (1) the effects of hearing loss on the neural encoding of speech allowing for behavioral detection and discrimination; (2) improvements in the neural processing of speech with amplification (hearing aids, cochlear implants); and (3) the impact of auditory training on the neural processing of speech. Studies in these three areas are reviewed and implications for audiologists are discussed.     

Brainstem auditory evoked potentials with speech stimulus in neonates

IntroductionBrainstem auditory evoked potentials in response to complex sounds, such as speech sounds, investigate the neural representation of these sounds at subcortical levels, and faithfully reflect the stimulus characteristics. However, there are few studies that utilize this type of stimulus; for it to be used in clinical practice it is necessary to establish standards of normality through studies performed in different populations.ObjectiveTo analyze the latencies and amplitudes of the waves obtained from the tracings of brainstem auditory evoked potentials using speech stimuli in Brazilian neonates with normal hearing and without auditory risk factors.Methods21 neonates with a mean age of 9 days without risk of hearing loss and with normal results at the neonatal hearing screening were evaluated according to the Joint Committee on Infant Hearing protocols. Auditory evoked potentials were performed with speech stimuli (/da/ syllable) at the intensity of 80 dBNA and the latency and amplitude of the waves obtained were analyzed.ResultsIn the transient portion, we observed a 100% response rate for all analyzable waves (Wave I, Wave III, Wave V and Wave A), and these waves exhibited a latency <10 ms. In the sustained portion, Wave B was identified in 53.12% of subjects; Wave C in 75%; Wave D in 90.62%; Wave E in 96.87%; Wave F in 87.5% and Wave O was identified in 87.5% of subjects. The observed latency of these waves ranged from 11.51 ms to 52.16 ms. Greater similarity was observed for the response latencies, as well as greater amplitude variation in the studied group.ConclusionsAlthough the wave morphology obtained for brainstem evoked potentials with speech stimulation in neonates is quite similar to that of adults, a longer latency and greater variation in amplitude were observed in the waves analyzed.     

Brainstem auditory evoked potentials with and without increased stimulus rate as diagnostic tool in brainstem minor transient changes

Two clinical groups of patients - 25 with Parkinson's disease and 17 with migraine - were evaluated using brainstem auditory evoked potentials (BAEP) to regular (10/s) and increased (55/s) stimulus rates. Each group of patients had an age-matched control group. The BAEP data were statistically evaluated, comparing the data of migraine patients during and between migraine spells, and the parkinsonian patients before and after L-dopa treatment. We believe that when group data are compared BAEP to an increased stimulus rate is an efficient tool for detecting even minor transient reversible physiologic changes of the brainstem.     

Automated cortical auditory evoked potentials threshold estimation in neonates

Introduction

The evaluation of cortical auditory evoked potential has been the focus of scientific studies in infants. Some authors have reported that automated response detection is effective in exploring these potentials in infants, but few have reported their efficacy in the search for thresholds.

The effect of stimulus choice on cortical auditory evoked potentials (CAEP): Consideration of speech segment positioning within naturally produced speech

Abstract

Objective: Cortical auditory evoked potentials (CAEPs) can be elicited to stimuli generated from different parts of speech. The aim of this study was to compare the phoneme /?/ from word medial and word initial positions and its influence on the CAEP. Design: Stimuli from word medial positions were found to have shorter rise times compared to the same phonemes from word initial positions. A repeated measures design was carried out with CAEPs elicited using /?/ from a word initial and a word medial position. Study sample: Sixteen individuals with audiometric thresholds within normal limits participated in the study. Results: Stimuli /?/ from a word medial position elicited CAEPs with significantly larger amplitudes and shorter latencies compared to /?/ from a word initial position (p < 0.05). Conclusions: Findings from this study, incorporating naturally produced speech sounds, suggest the need to consider spectral and temporal variations when choosing stimuli to optimize the amplitude and latency characteristics of the CAEP. Overall, findings illustrate good test-retest reliability of CAEP measures using speech stimuli with clinical equipment.     

Cervical and ocular vestibular evoked myogenic potentials are sensitive to stimulus phase

Sinusoidal forces with frequencies of 100 and 500 Hz and initial positive or negative polarities were delivered to the mastoids and Fz in normal subjects. We investigated whether the cVEMPs and oVEMPs evoked were sensitive to the polarity (phase) of vibration. With mastoid stimulation at 100 Hz, medial head acceleration produced cVEMPs with earlier latency (15.5 ms) than lateral acceleration (19.7 ms) and oVEMPs with later latency (13.8 ms) than lateral acceleration (10.6 ms). As the stimulus frequency increased, the difference in latency decreased, but was still present at 500 Hz. A similar pattern occurred following stimulation at Fz. Our results show that the initial direction of bone-conducted vibration affects both cVEMP and oVEMP properties even at relatively high frequencies.     

Evaluation of cochlear implant benefit with auditory cortical evoked potentials

Endogenous P300 and exogenous slow vertex potentials were obtained with tone and speech stimuli in a group of five children using a cochlear implant (CI) with poor speech recognition (group A) and compared with those from another group of five children using a CI with good speech recognition (group B). The responses were also compared to those of children with normal hearing (n= 14) and a group of adult CI users (n=9). N1 and P2 latencies of CI group A and group B were prolonged compared to those of normally-hearing children. In group A, P300 was present when contrasts with tone stimuli were used. When speech stimuli were used, P300 potentials were absent or delayed. P300 potentials obtained in group B were no different from those obtained in normally-hearing children. It is suggested that the poor results evoked with speech stimuli in contrast to those evoked with pure-tone stimuli in group A are due to the immaturity of (sub) cortical generators associated with acoustical and phonetic processing. In contrast to the children in group B, all children in group A suffered from congenital deafness.     

The dependence of early acoustically evoked potentials on age

Summary Early acoustically evoked potentials (brain-stem potentials, latency up to 10 ms) were compared in two groups of varying age (25 and 63 years old, respectively). Although no age-dependent change in potential amplitudes was detected, a significantly longer latency period in older subjects was established for potentials III, IV, V, and VII at all levels of stimulus intensity. However, the difference in latency time between two consecutive responses shows that potentials IV and VI followed more quickly in the older than in the younger persons. An explanation of this discovery is attempted.     

The dependence of early acoustically evoked potentials on age

Early acoustically evoked potentials (brain-stem potentials, latency up to 10 ms) were compared in two groups of varying age (25 and 63 years old, respectively). Although no age-dependent change in potential amplitudes was detected, a significantly longer latency period in older subjects was established for potentials III, IV, V, and VII at all levels of stimulus intensity. However, the difference in latency time between two consecutive responses shows that potentials IV and VI followed more quickly in the older than in the younger persons. An explanation of this discovery is attempted.     

Local auditory evoked potentials and effects of pure tones on click evoked potentials in the pigeon

Local auditory evoked potentials (AEPs) in the pigeon were recorded from the nucleus magnocellularis (NM), nucleus angularis (NA) and Field L with tungsten microelectrodes. In the NM and NA, AEPs in response to clicks were always suppressed by application of continuous pure tones at specific frequencies as is usual for simultaneous masking. In the NA, frequencies of continuous pure tones which produced maximum suppression and frequencies of tone bursts which elicited maximum response both centered around 0.8 kHz. The NM tended to respond similarly. In Field L, however, amplitudes of the AEPs to clicks were suppressed, enhanced, both suppressed and enhanced, or unaffected by presentation of continuous pure tones at specific frequencies. The frequencies of tone bursts which caused maximum AEP were vaguely related to the frequencies of continuous pure tones which elicited maximum suppression of the AEPs to clicks. On the other hand, enhancement was produced by 1-2 kHz continuous pure tones independent of the frequency of tone bursts that produced maximum AEP. It was concluded that enhancement, suppression and lack of effect in Field L were due to some central neural mechanism.     

纯音和言语刺激声强度对听觉事件相关电位的影响

目的:探讨分别以纯音和言语作刺激声时声强度对听觉事件相关电位(AERP)的影响.方法:采用不同强度的纯音和言语作为刺激声对正常年青人进行AERP测试,比较纯音和言语诱出典型P300的强度范围,分析不同强度对P300的影响是否同时存在于纯音和言语刺激声.结果:言语刺激声比纯音更容易在40～70 dBSL范围内连续记录到典型波形,差异有统计学意义(P＜0.01).言语或纯音刺激时,强度对P300潜伏期的影响差异均有统计学意义(P＜0.01),在40～70 dBSL范围内潜伏期随强度增加而减小,强度对P300幅值的影响差异均无统计学意义.结论:强度对AERP的影响在纯音和言语刺激时基本相同,但言语得到典型AERP波形的强度范围较纯音宽,其原因可能与言语刺激声包含的信息较纯音刺激声丰富,受试者对汉语言语刺激声较纯音更熟悉有关.     

Galvanic vestibular evoked myogenic potentials: normative data and the effect of age

IntroductionGalvanic vestibular evoked myogenic potentials evaluate vestibular nerve responses using electric stimulation by records collected from the sternocleidomastoid muscle. A normal vestibular evoked myogenic potential response consists of the first positive, P1, and negative, N1, peaks. The response can be affected by factors such as age and gender and is also consequential in the diagnosis of pathologies.ObjectivesThe present study was performed to obtain normative data on healthy adults, to help in diagnosis by establishing clinical norms as well as to investigate changing test parameters with age in galvanic vestibular evoked myogenic potentials.MethodsA total of 100 healthy participants were included in the study. Galvanic vestibular evoked myogenic potential (current 3 mA, duration 1 ms) was performed randomly on both ears of each participant. The participants between the ages of 18–65 (mean age 39.7 ± 13.9) were divided into 5 groups according to their ages. Normative data of galvanic vestibular evoked myogenic potentials parameters were calculated in groups and in total, and age-related changes were examined.ResultsThe galvanic vestibular evoked myogenic potential waveform was elicited from all participants (200 ears). The latency of P1 and N1 was 7.82 ± 3.29 ms and 22.06 ± 3.95 ms, respectively. The P1?N1 amplitude value was 66.64 ± 24.5 µV. The percentage of vestibular asymmetry was 16.29 ± 11.99%. The latencies of P1 and N1 and P1?N1 amplitude values demonstrated significant differences among different age groups (p < 0.01).ConclusionsThe results of this study show that as age increased, latencies were prolonged, and amplitudes gradually decreased. The normative data aids in the diagnosis of retrolabyrinthine lesions and the increase in the clinical use of galvanic vestibular evoked myogenic potentials.     

Effects of stimulus conditions on vestibular evoked myogenic potentials in healthy subjects

Background: Characteristics of vestibular evoked myogenic potentials (VEMPs) depend on stimulus conditions.

Objective: To determine the optimal stimulus conditions for cervical and ocular VEMPs.

Methods: Participants were 23 healthy subjects. We compared air-conducted cervical and ocular VEMPs elicited by various tone-burst conditions (frequencies 500–1,000?Hz, rise/fall times 1–2?ms, and plateau times 0–6?ms) with an intensity of 105?dB normal hearing level. Effects of simultaneous contralateral masking noise on VEMPs were also evaluated.

Results: The largest cervical VEMP amplitudes were elicited by 500–750?Hz and 2–6?ms plateau time-tone-bursts, and the largest ocular VEMP amplitudes by 750?Hz and 2–4?ms plateau time-tone-bursts. Repeatability of the latency was better at 1?ms than at 2?ms rise/fall time in both VEMPs. In both VEMPs, masking noise reduced amplitude, and in ocular VEMP, amplitudes were significantly larger at the left ear stimulation than the right.

Conclusion: Optimal tone-burst stimulation for both VEMPs seemed to be 500–750?Hz frequency and 1/2/1?ms rise/plateau/fall time without contralateral masking noise. Ocular VEMP amplitudes from left ear stimulation were originally larger than those from right ear stimulation.