Cortical Auditory Evoked Potential Indices of Impaired Sensory Gating in People With Chronic Tinnitus.

OBJECTIVES: The primary aim of this study was to evaluate whether there is cortical auditory evoked potential (CAEP) evidence of impaired sensory gating in individuals with tinnitus. On the basis of the proposed mechanism of tinnitus generation, including a thalamocortical inhibitory deficit, it was hypothesized that individuals with tinnitus would lack the normal inhibitory effect on the second CAEP response in a paired-click sensory gating paradigm, resulting in larger sensory gating ratios in individuals with tinnitus relative to age-, sex-, and hearing-matched controls. Further, this study assessed the relative predictive influence of tinnitus presence versus other related individual characteristics (hearing loss, age, noise exposure history, and speech perception in noise) on sensory gating. DESIGN: A paired-click CAEP paradigm was used to measure sensory gating outcomes in an independent group's experimental design. Adults who perceived chronic unilateral or bilateral tinnitus were matched with control group counterparts without tinnitus by age, hearing, and sex (n = 18; 10 females, eight males in each group). Amplitude, area, and latency sensory gating ratios were determined for measured P1, N1, and P2 responses evoked by the first and second click in the paradigm and compared between groups by independent t tests. The relative influence of tinnitus (presence/absence), age (in years), noise exposure history (subjective self-report), hearing loss (pure-tone audiometric thresholds), and speech perception in noise (signal to noise ratio-50) on sensory gating was determined based on the proportional reduction in error associated with each variable using multiple regression. RESULTS: A significantly larger was identified in the tinnitus group relative to the control group, consistent with the hypothesis of poorer sensory gating and poorer thalamocortical inhibition in individuals with chronic tinnitus. On the basis of the proportional reduction in error, the influence of tinnitus presence better predicted compared with other related individual characteristics (age, noise exposure history, hearing loss, and speech perception in noise). CONCLUSIONS: Results consistent with poorer sensory gating, including a larger , were found for the tinnitus group compared with the controls. This finding supported a thalamocortical inhibitory deficit in the tinnitus group and suggests that individuals with tinnitus may have poorer sensory gating. However, the tinnitus group did differ from controls in meaningful ways including having worse pure-tone thresholds in the extended high-frequency region, lower high-frequency distortion product otoacoustic emissions, and poorer speech perception in noise. Although tinnitus best predicted sensory gating outcomes, the specific effects of tinnitus presence versus absence and other individual characteristics on sensory gating cannot be completely separated.

Onset-offset cortical auditory evoked potential amplitude differences indicate auditory cortical hyperactivity and reduced inhibition in people with tinnitus.

OBJECTIVE: The current study investigates evidence of hypothesized reduced central inhibition and/or increased excitation in individuals with tinnitus by evaluating cortical auditory onset versus offset responses. METHODS: Cortical auditory evoked potentials (CAEPs) were recorded to the onset and offset of 3-second white noise stimuli in tinnitus and control groups matched in pairs by age, hearing, and sex (n = 26 total). Independent t-tests and 2-way mixed model ANOVA were used to evaluate onset-offset differences in amplitude, area, and latency of CAEP components by group. The predictive influence of tinnitus presence and associated participant characteristics on CAEP outcomes was assessed by multiple regression proportional reduction in error. RESULTS: The tinnitus group had significantly larger onset minus offset P2 amplitudes (ΔP2 amplitudes) than control group participants. No other component variables differed significantly. ΔP2 amplitude was best predicted by tinnitus status and not significantly influenced by other variables such as hearing loss or age. CONCLUSIONS: Hypothesized reduced central inhibition and/or increased excitation in tinnitus participants was partially supported by a group difference in ΔP2 amplitude. SIGNIFICANCE: This was the first study to evaluate CAEP onset minus offset differences to investigate changes in central excitation/inhibition in individuals with tinnitus versus controls in matched groups.

Informational Masking Effects of Speech Versus Nonspeech Noise on Cortical Auditory Evoked Potentials.

Purpose Background noise has been categorized as energetic masking due to spectrotemporal overlap of the target and masker on the auditory periphery or informational masking due to cognitive-level interference from relevant content such as speech. The effects of masking on cortical and sensory auditory processing can be objectively studied with the cortical auditory evoked potential (CAEP). However, whether effects on neural response morphology are due to energetic spectrotemporal differences or informational content is not fully understood. The current multi-experiment series was designed to assess the effects of speech versus nonspeech maskers on the neural encoding of speech information in the central auditory system, specifically in terms of the effects of speech babble noise maskers varying by talker number. Method CAEPs were recorded from normal-hearing young adults in response to speech syllables in the presence of energetic maskers (white or speech-shaped noise) and varying amounts of informational maskers (speech babble maskers). The primary manipulation of informational masking was the number of talkers in speech babble, and results on CAEPs were compared to those of nonspeech maskers with different temporal and spectral characteristics. Results Even when nonspeech noise maskers were spectrally shaped and temporally modulated to speech babble maskers, notable changes in the typical morphology of the CAEP in response to speech stimuli were identified in the presence of primarily energetic maskers and speech babble maskers with varying numbers of talkers. Conclusions While differences in CAEP outcomes did not reach significance by number of talkers, neural components were significantly affected by speech babble maskers compared to nonspeech maskers. These results suggest an informational masking influence on neural encoding of speech information at the sensory cortical level of auditory processing, even without active participation on the part of the listener.

Informational Masking Effects of Similarity and Uncertainty on Early and Late Stages of Auditory Cortical Processing.

PURPOSE: Understanding speech in a background of other people talking is a difficult listening situation for hearing-impaired individuals, and even for those with normal hearing. Speech-on-speech masking is known to contribute to increased perceptual difficulty over nonspeech background noise because of informational masking provided over and above the effects of energetic masking. While informational masking research has identified factors of similarity and uncertainty between target and masker that contribute to reduced behavioral performance in speech background noise, critical gaps in knowledge including the underlying neural-perceptual processes remain. By systematically manipulating aspects of acoustic similarity and uncertainty in the same auditory paradigm, the current study examined the time course and objectively quantified these informational masking effects at both early and late stages of auditory processing using auditory evoked potentials (AEPs). METHOD: Thirty participants were included in a cross-sectional repeated measures design. Target-masker similarity was manipulated by varying the linguistic/phonetic similarity (i.e., language) of the talkers in the background. Specifically, four levels representing hypothesized increasing levels of informational masking were implemented: (1) no masker (quiet); (2) Mandarin; (3) Dutch; and (4) English. Stimulus uncertainty was manipulated by task complexity, specifically presentation of target-to-target interval (TTI) in the auditory evoked paradigm. Participants had to discriminate between English word stimuli (/bæt/ and /pæt/) presented in an oddball paradigm under each masker condition pressing buttons to either the target or standard stimulus. Responses were recorded simultaneously for P1-N1-P2 (standard waveform) and P3 (target waveform). This design allowed for simultaneous recording of multiple AEP peaks, as well as accuracy, reaction time, and d' behavioral discrimination to button press responses. RESULTS: Several trends in AEP components were consistent with effects of increasing linguistic/phonetic similarity and stimulus uncertainty. All babble maskers significantly affected outcomes compared to quiet. In addition, the native language English masker had the largest effect on outcomes in the AEP paradigm, including reduced P3 amplitude and area, as well as decreased accuracy and d' behavioral discrimination to target word responses. AEP outcomes for the Mandarin and Dutch maskers, however, were not significantly different across any measured component. Latency outcomes for both N1 and P3 also supported an effect of stimulus uncertainty, consistent with increased processing time related to greater task complexity. An unanticipated result was the absence of the interaction of linguistic/phonetic similarity and stimulus uncertainty. CONCLUSIONS: Observable effects of both similarity and uncertainty were evidenced at a level of the P3 more than the earlier N1 level of auditory cortical processing suggesting that higher-level active auditory processing may be more sensitive to informational masking deficits. The lack of significant interaction between similarity and uncertainty at either level of processing suggests that these informational masking factors operated independently. Speech babble maskers across languages altered AEP component measures, behavioral detection, and reaction time. Specifically, this occurred when the babble was in the native/same language as the target, while the effects of foreign language maskers did not differ. The objective results from this study provide a foundation for further investigation of how the linguistic content of target and masker and task difficulty contribute to difficulty understanding speech-in-noise.

Auditory and Cognitive Behavioral Performance Deficits and Symptom Reporting in Postconcussion Syndrome Following Mild Traumatic Brain Injury.

Purpose This study examined auditory deficits and symptom reporting in individuals with long-term postconcussion symptoms following a single mild traumatic brain injury (mTBI) compared to age- and gender-matched controls without a history of mTBI. Method Case history interviews, symptom questionnaires, and a battery of central auditory and neuropsychological tests were administered to 2 groups. The mTBI group was a civilian population recruited from a local concussion management program who were seeking rehabilitation for postconcussion-related problems in a postacute period between 3 and 18 months following injury. Symptom validity testing was included to assess the rate of possible insufficient test effort and its influence on scores for all outcome measures. Analyses of group differences in test scores were performed both with and without the participants who showed insufficient test effort. Rates of symptom reporting, correlations among symptoms and behavioral test outcomes, and the relationships between auditory and cognitive test performance were analyzed. Results The mTBI group reported a high rate of auditory symptoms and general postconcussion symptoms. Performance on neuropsychological tests of cognitive function showed some differences in raw scores between groups, but when effort was considered, there were no significant differences in the rate of abnormal performance between groups. In contrast, there were significant differences in both raw scores and the rate of abnormal performance between groups for some auditory tests when only considering participants with sufficient effort. Auditory symptoms were strongly correlated with other general postconcussion symptoms. Conclusions Significant auditory symptoms and evidence of long-term central auditory dysfunction were found in a subset of individuals who had chronic postconcussion symptoms after a single mTBI unrelated to blast trauma. The rate of abnormal performance on auditory behavioral tests exceeded the rate of abnormal performance on tests of cognitive function. Supplemental Material https://doi.org/10.23641/asha.8329955.

Impaired auditory processing and neural representation of speech in noise among symptomatic post-concussion adults.

Background: The purpose of the study was to examine auditory event-related potential (AERP) evidence of changes in earlier and later stages of auditory processing in individuals with long-term post-concussion problems compared to healthy controls, with a secondary aim of comparing AERPs by functional auditory behavioral outcomes. Methods: P1-N1-P2 complex and P300 components recorded to speech in quiet and background noise conditions were completed in individuals with ongoing post-concussion symptoms following mTBI and healthy controls. AERPs were also examined between sub-groups with normal or impaired auditory processing by behavioral tests. Results: Group differences were present for later stages of auditory processing (P300). Earlier components did not significantly differ by group overall but were more affected by noise in the mTBI group. P2 amplitude in noise differed between mTBI sub-groups with normal or impaired auditory processing. Conclusion: AERPs revealed differences between healthy controls and those with chronic post-concussion symptoms following mTBI at a later stage of auditory processing (P300). Neural processing at the earlier stage (P1-N1-P2) was more affected by noise in the mTBI group. Preliminary evidence suggested that it may be only the proportion of individuals with functional evidence of central auditory dysfunction with changes in AERPs at earlier stages of processing.

Comparison of Silent Gap in Noise Cortical Auditory Evoked Potentials in Matched Tinnitus and No-Tinnitus Control Subjects.

Purpose Previous research suggests the existence of gap detection impairments because of tinnitus. The current study aimed to determine whether there was objective evidence of gap impairment in individuals with tinnitus by recording silent gap in white noise cortical auditory evoked potentials (CAEPs) in a chronic tinnitus group and a no-tinnitus group. The results were compared to previous gap-evoked potential and behavioral gap detection studies. Method Chronic tinnitus and no-tinnitus groups were formed by matching pairs of subjects ( n = 26) based on age, gender, and hearing thresholds. Behaviorally determined gap detection thresholds were used to define the electrophysiological gap duration conditions of subthreshold, threshold, and suprathreshold gaps in white noise. Amplitude, latency, and area of the CAEP were analyzed by group and condition using mixed-model analyses of variance. Results Across all participants, as the duration of the gap increased, amplitude and area of the CAEP increased. There were no significant differences by tinnitus status between groups for any outcome measures, except for a significant interaction between group and gap duration for P1 latency. Conclusions Silent gap-evoked CAEPs can be recorded in adults with and without tinnitus. Amplitude and area were sensitive to gap duration across groups; latency was not. Contrary to hypotheses, there was little evidence supporting differences in gap-evoked CAEPs between the tinnitus and control groups. Stimulus and other factors that may have contributed to the lack of a group difference in the current study are discussed, as well as implications for future studies of objective measures of tinnitus perception. Supplemental Material https://doi.org/10.23641/asha.7822601.

Informational Masking Effects on Neural Encoding of Stimulus Onset and Acoustic Change.

OBJECTIVE: Recent investigations using cortical auditory evoked potentials have shown masker-dependent effects on sensory cortical processing of speech information. Background noise maskers consisting of other people talking are particularly difficult for speech recognition. Behavioral studies have related this to perceptual masking, or informational masking, beyond just the overlap of the masker and target at the auditory periphery. The aim of the present study was to use cortical auditory evoked potentials, to examine how maskers (i.e., continuous speech-shaped noise [SSN] and multi-talker babble) affect the cortical sensory encoding of speech information at an obligatory level of processing. Specifically, cortical responses to vowel onset and formant change were recorded under different background noise conditions presumed to represent varying amounts of energetic or informational masking. The hypothesis was, that even at this obligatory cortical level of sensory processing, we would observe larger effects on the amplitude and latency of the onset and change components as the amount of informational masking increased across background noise conditions. DESIGN: Onset and change responses were recorded to a vowel change from /u-i/ in young adults under four conditions: quiet, continuous SSN, eight-talker (8T) babble, and two-talker (2T) babble. Repeated measures analyses by noise condition were conducted on amplitude, latency, and response area measurements to determine the differential effects of these noise conditions, designed to represent increasing and varying levels of informational and energetic masking, on cortical neural representation of a vowel onset and acoustic change response waveforms. RESULTS: All noise conditions significantly reduced onset N1 and P2 amplitudes, onset N1-P2 peak to peak amplitudes, as well as both onset and change response area compared with quiet conditions. Further, all amplitude and area measures were significantly reduced for the two babble conditions compared with continuous SSN. However, there were no significant differences in peak amplitude or area for either onset or change responses between the two different babble conditions (eight versus two talkers). Mean latencies for all onset peaks were delayed for noise conditions compared with quiet. However, in contrast to the amplitude and area results, differences in peak latency between SSN and the babble conditions did not reach statistical significance. CONCLUSIONS: These results support the idea that while background noise maskers generally reduce amplitude and increase latency of speech-sound evoked cortical responses, the type of masking has a significant influence. Speech babble maskers (eight talkers and two talkers) have a larger effect on the obligatory cortical response to speech sound onset and change compared with purely energetic continuous SSN maskers, which may be attributed to informational masking effects. Neither the neural responses to the onset nor the vowel change, however, were sensitive to the hypothesized increase in the amount of informational masking between speech babble maskers with two talkers compared with eight talkers.

Hearing Loss and Age-Induced Changes in the Central Auditory System Measured by the P3 Response to Small Changes in Frequency.

BACKGROUND: Recent behavioral studies have suggested that individuals with sloping audiograms exhibit localized improvements in frequency discrimination in the frequency region near the drop in hearing. Auditory-evoked potentials may provide evidence of such cortical plasticity and reorganization of frequency maps. PURPOSE: The objective of this study was to evaluate electrophysiological evidence of cortical plasticity related to cortical frequency representation and discrimination abilities in older individuals with high-frequency sensorineural hearing loss (SNHL). It was hypothesized that the P3 response in this group would show evidence of physiological reorganization of frequency maps and enhanced neural representation at the edge of their high-frequency loss due to their restricted SNHL. RESEARCH DESIGN: The P3 auditory event-related potential in response to small frequency changes was recorded in a repeated measures design using an oddball paradigm that presented upward and downward frequency changes of 2%, 5%, and 20% to three groups of listeners. STUDY SAMPLE: P3 recordings from a group of seven older individuals with a restricted sloping hearing loss >1000 or 2000 Hz was compared to two control groups of younger (n = 7) and older (n = 7) individuals with normal hearing/borderline normal hearing through 4000 Hz. DATA COLLECTION AND ANALYSIS: The auditory P3 was recorded using an oddball paradigm (80%/20%) with the standard tone at the highest frequency of normal hearing in the hearing-impaired participants, also known as the edge frequency (EF). EFs were either 1000 or 2000 Hz for all participants. The target tones represented upward and downward frequency changes of 2%, 5%, and 20% from the standard tones of either 1000 or 2000 Hz. Waveforms were recorded using a two-channel clinical-evoked potential system. Latency and amplitude of the P300 peak were analyzed across groups for the three frequency conditions using repeated measures analysis of variance. RESULTS: The results of this study suggest that the P3 response can be elicited by frequency changes as small as 2-5%. P3 responses at the EF of hearing loss were present and larger in amplitude for more participants with a sloping hearing loss compared to age-matched normal-hearing peers tested at the same frequencies. As a result, the older participants with sloping hearing losses had P3 responses more similar to the younger normal-hearing participants than their age-matched peers with normal hearing. CONCLUSIONS: These preliminary results partially support the idea of enhanced cortical representation of frequency at the EF of localized SNHL in older adults that is not purely due to age.

Brainstem Evoked Potential Indices of Subcortical Auditory Processing After Mild Traumatic Brain Injury.

OBJECTIVES: The primary aim of this study was to assess subcortical auditory processing in individuals with chronic symptoms after mild traumatic brain injury (mTBI) by measuring auditory brainstem responses (ABRs) to standard click and complex speech stimuli. Consistent with reports in the literature of auditory problems after mTBI (despite normal-hearing thresholds), it was hypothesized that individuals with mTBI would have evidence of impaired neural encoding in the auditory brainstem compared to noninjured controls, as evidenced by delayed latencies and reduced amplitudes of ABR components. We further hypothesized that the speech-evoked ABR would be more sensitive than the click-evoked ABR to group differences because of its complex nature, particularly when recorded in a background noise condition. DESIGN: Click- and speech-ABRs were collected in 32 individuals diagnosed with mTBI in the past 3 to 18 months. All mTBI participants were experiencing ongoing injury symptoms for which they were seeking rehabilitation through a brain injury rehabilitation management program. The same data were collected in a group of 32 age- and gender-matched controls with no history of head injury. ABRs were recorded in both left and right ears for all participants in all conditions. Speech-ABRs were collected in both quiet and in a background of continuous 20-talker babble ipsilateral noise. Peak latencies and amplitudes were compared between groups and across subgroups of mTBI participants categorized by their behavioral auditory test performance. RESULTS: Click-ABR results were not significantly different between the mTBI and control groups. However, when comparing the control group to only those mTBI subjects with measurably decreased performance on auditory behavioral tests, small differences emerged, including delayed latencies for waves I, III, and V. Similarly, few significant group differences were observed for peak amplitudes and latencies of the speech-ABR when comparing at the whole group level but were again observed between controls and those mTBI subjects with abnormal behavioral auditory test performance. These differences were seen for the onset portions of the speech-ABR waveforms in quiet and were close to significant for the onset wave. Across groups, quiet versus noise comparisons were significant for most speech-ABR measures but the noise condition did not reveal more group differences than speech-ABR in quiet, likely because of variability and overall small amplitudes in this condition for both groups. CONCLUSIONS: The outcomes of this study indicate that subcortical neural encoding of auditory information is affected in a significant portion of individuals with long-term problems after mTBI. These subcortical differences appear to relate to performance on tests of auditory processing and perception, even in the absence of significant hearing loss on the audiogram. While confounds of age and slight differences in audiometric thresholds cannot be ruled out, these preliminary results are consistent with the idea that mTBI can result in neuronal changes within the subcortical auditory pathway that appear to relate to functional auditory outcomes. Although further research is needed, clinical audiological evaluation of individuals with ongoing post-mTBI symptoms is warranted for identification of individuals who may benefit from auditory rehabilitation as part of their overall treatment plan.

The Application of the International Classification of Functioning, Disability and Health to Functional Auditory Consequences of Mild Traumatic Brain Injury.

This article reviews the auditory consequences of mild traumatic brain injury (mTBI) within the context of the International Classification of Functioning, Disability and Health (ICF). Because of growing awareness of mTBI as a public health concern and the diverse and heterogeneous nature of the individual consequences, it is important to provide audiologists and other health care providers with a better understanding of potential implications in the assessment of levels of function and disability for individual interdisciplinary remediation planning. In consideration of body structures and function, the mechanisms of injury that may result in peripheral or central auditory dysfunction in mTBI are reviewed, along with a broader scope of effects of injury to the brain. The activity limitations and participation restrictions that may affect assessment and management in the context of an individual's personal factors and their environment are considered. Finally, a review of management strategies for mTBI from an audiological perspective as part of a multidisciplinary team is included.

Erratum: The Application of the International Classification of Functioning, Disability and Health to Functional Auditory Consequences of Mild Traumatic Brain Injury.

[This corrects the article DOI: 10.1055/s-0036-1584409.].

Identification of conductive hearing loss in young infants using tympanometry and wideband reflectance.

OBJECTIVE: The goal of the study was to evaluate the effectiveness of tympanometry and wideband reflectance (WBR) in detecting conductive hearing loss (CHL) in young infants. METHODS: Type of hearing loss was determined using auditory brainstem response using air- and bone-conducted tone bursts in 84 ears from 70 infants (median age = 10 weeks). Of these 84 ears, 60 are included in the current analysis: 43 with normal hearing (NH) and 17 with CHL. Tympanometry was measured using probe tone frequencies of 226, 678, and 1000 Hz. Tympanograms were evaluated in two ways: (1) Acoustic middle ear admittance (Ya, in millimhos); and (2) two-category classification (normal/abnormal), as described by Baldwin (2006). Measures of Ya were evaluated in two ways: by admittance-magnitude tympanograms and calculated admittance magnitude from subcomponents (conductance and susceptance). WBR was measured in response to a chirp stimulus after probe calibration. WBR was analyzed into thirteen 1/3 octave bands. Tests for statistical differences for two-category classification were analyzed using Chi-squared and Ya, and WBR were analyzed using repeated-measures analyses of variances. Cohen's d and likelihood ratios were computed for comparison with statistically significant differences. RESULTS: Ya measured with 678- and 1000 Hz probe tones was significantly different between ears with CHL and NH. Two-category classification of tympanograms using a 1000 Hz probe tone was significantly different between ears with CHL and NH. Neither two-category classification nor Ya was significantly different between ears identified with CHL and NH using a 226 Hz probe tone. WBR was significantly higher in the frequency bands 800 to 2500 Hz and in the frequency band centered at 6300 Hz in infants with CHL. Effect sizes (Cohen's d) were greater than 2 for several WBR frequency bands and Ya measured with 1000 Hz probe tones. The results were similar for calculations of Ya from admittance-magnitude and subcomponent tympanograms. Positive likelihood ratios for WBR ranged between 8.1 and 38, and those for Ya using 1000 Hz ranged between 12.5 and 32. CONCLUSIONS: CHL in young infants can be detected well with WBR or tympanometry using probe frequencies of 678 and 1000 Hz.

Brain stem responses to speech in younger and older adults.

OBJECTIVE: This experiment was designed to evaluate whether neural encoding of speech features at the brain stem level is altered in the aging auditory system. In addition, the effect of minimal peripheral hearing loss on the auditory brain stem response (ABR) evoked by speech stimuli and interactions with aging were examined. DESIGN: Speech-evoked ABRs (S-ABRs) were recorded using a synthetic 40-msec /da/ stimulus from both ears of participants in two groups: normal-hearing younger adults (n = 19) and normal-hearing older adults (n = 18). Latencies and amplitude for S-ABR peaks representing neural responses to the onset and offset of the speech syllable as well as a sustained frequency following response to the vowel content were analyzed. The role of hearing threshold differences between groups and the reduced overall stimulus level on the S-ABR were also examined. In addition, click-evoked ABRs (C-ABRs) were obtained from all participants, and age-group differences in the neural response to both types of stimuli at the brain stem level were compared. RESULTS: S-ABR latencies, amplitudes, and sustained response mean data were obtained for younger adults and older adults. Older adults were found to have significantly smaller C-ABRs with longer latencies, despite all latencies falling within normal limits. Older adults also had significantly smaller onset and offset responses for the S-ABR, with significantly delayed offset latencies in response to this synthetic consonant-vowel syllable. Many of the C-ABR and S-ABR variables were found to significantly correlate with high-frequency audiometric thresholds, and few of the group differences remained significant when this was taken into account. The remaining significant S-ABR effects were decreased amplitude at the onset and significantly delayed offset responses in the older group. These effects were different from those of simply decreasing the overall stimulus level, which caused significant shifts in latency across the entire S-ABR. CONCLUSIONS: Results of this study partially supported the hypothesis of age-related differences in neural processing of speech at the brain stem level. There were significant delays in the timing of the offset portion of the S-ABR in older listeners compared with their younger counterparts, even after accounting for the differences in peripheral hearing threshold between groups. There were also significant reductions in amplitude of the S-ABR at the onset. These results are consistent with a reduction in neural synchrony in older adults to transient components of both speech and nonspeech sounds. However, sustained components of the S-ABR, which follow the harmonic components of the syllable, showed group differences but were not significant after adjusting for peripheral hearing loss, suggesting that they may be more affected by hearing sensitivity and other peripheral changes. These results support further investigation into the ability of the aging auditory system to encode temporal cues at the brain stem level, particularly the response to speech stimulus offset and its relationship to speech perception and temporal processing abilities.

Accuracy and time efficiency of two ASSR analysis methods using clinical test protocols.

BACKGROUND: The number of commercially available evoked potential systems implementing multiple-frequency auditory steady-state response (ASSR) techniques has increased over the last several years. The majority of data in the multiple-frequency ASSR literature have been obtained using time-domain averaging and Fast Fourier Transform (FFT) techniques with F-test statistical analysis. Another commercially available analysis method has been introduced using an adaptive filtering algorithm called the Fourier Linear Combiner (FLC). No previous investigation has evaluated the performance of the FLC method, nor compared the two techniques. In addition, there is a need for evaluation of clinical protocols for ASSR testing using these available commercial systems that balance time efficiency and accuracy in estimating threshold. PURPOSE: (1) To determine whether ASSR thresholds, the relationship between ASSR and behavioral thresholds, and clinical test time are affected by the ASSR analysis method when comparing two commercially available systems for multiple-frequency ASSR. (2) To investigate the use of clinical ASSR test protocols of varying recording length, and the effect on accuracy and time efficiency, using these two commercially available analysis methods. RESEARCH DESIGN AND STUDY SAMPLE: ASSR threshold searches were completed on a group of 20 normal-hearing and 20 hearing-impaired adult participants using two different analysis methods, FFT and FLC, under separate, independent, tests as well under simultaneous recording conditions. DATA COLLECTION AND ANALYSIS: Three experiments were completed: (1) independent assessment of ASSR thresholds using the FFT and FLC methods separately, (2) simultaneous recording of ASSR for both the FFT and FLC method, and (3) an automated threshold search protocol using the FLC method. Variables analyzed for Experiments 1 and 3 included ASSR thresholds, the difference between ASSR and behavioral threshold, and total test time. For Experiment 2, the number of detected ASSRs per method, the agreement between methods, and the time per detected ASSR were evaluated. RESULTS AND CONCLUSIONS: ASSR thresholds and the relationship between ASSR and behavioral thresholds were found to be in line with those reported in the literature for multiple-frequency ASSR for both the FLC and FFT methods. ASSR thresholds were found to be significantly higher for the FLC method for the low frequencies, but not for the high frequencies, when tested independently. Correlations between ASSR and behavioral thresholds, however, were found to be the same across methods. Overall, it did not appear that either analysis method held an advantage in terms of accuracy or overall test time in independent comparisons using the protocol implemented in the current study. The time benefits of an automated protocol were significant, although with compromised test accuracy. The results of this study suggest critical clinical decision making is a necessary part of the ASSR protocol in order to decrease false positive and false negative responses and to increase overall efficiency.

Infant air and bone conduction tone burst auditory brain stem responses for classification of hearing loss and the relationship to behavioral thresholds.

OBJECTIVE: A clinical protocol for diagnosing hearing loss (HL) in infants designed to meet early intervention guidelines was used with the goals of providing normative data for (1) frequency-specific tone burst auditory brain stem response (TBABR) thresholds by air conduction (AC) and bone conduction (BC) in early infancy used to classify type and severity of HL, (2) ear-specific behavioral thresholds for these same infants by 1 yr of age, and (3) the relationship between TBABR thresholds and behavioral thresholds for this group of infants. DESIGN: AC- and BC-TBABRs were measured in young infants (mean age, <3 mo) under natural sleep to classify the type and severity of HL (conductive, sensorineural, or mixed). A small group of normal-hearing adults undergoing the same TBABR protocol served as a control group. Threshold and latency data for AC- and BC-ABR were analyzed for infants classified as having normal hearing and for those with and without conductive HL. The ability to detect conductive HL based on ABR latencies evoked by clicks presented at 80 dB nHL was assessed. Behavioral thresholds using visual reinforcement audiometry (VRA) were measured in infants at a mean age of approximately 10 mo. The relationship between TBABR and behavioral thresholds obtained in infancy was analyzed, and the prediction of behavioral thresholds from TBABR thresholds was examined. RESULTS: Mean TBABR thresholds in young infants with normal hearing tested under natural sleep were similar to previously published data. The relationship between AC- and BC-TBABR thresholds differed as a function of stimulus frequency for infants but not adults. A mean air-bone gap (ABG) of 15 dB was present at 500 Hz even in normal-hearing infants, with those infants classified as having conductive HL presenting with substantially larger ABGs. Wave V latency functions for AC- and BC-TBABR also differed between infants and adults as a function of frequency. Infant BC-TBABR latencies were well matched between those with normal hearing and conductive HL, whereas AC-TBABR latency functions separated these groups. Mean VRA thresholds using insert phones in normal-hearing infants tested were between 14 and 17 dB HL for all three test frequencies at a mean age of 9.7 mo. Correlations between TBABR and VRA thresholds, both obtained during infancy, were strong for all three test frequencies (r = 0.86, 0.90, and 0.91 for 500, 2000, and 4000 Hz, respectively). CONCLUSIONS: AC- and BC-TBABR results can be readily obtained in young infants under natural sleep and were used to classify the type of HL based on the absolute threshold and the size of the ABG. Differences in wave V latency functions for TBABR by AC and BC and wave I and V latencies of the high-level click ABR also distinguish between infants with and without TBABR ABGs. Ear-specific behavioral responses can be obtained at levels under 20 dB HL in normal-hearing infants younger than 1 yr using VRA, and these behavioral thresholds correlate well with TBABR thresholds obtained on average 6.5 mo previously in this population. The current results suggest that protocols for obtaining AC- and BC-TBABR and behavioral thresholds that meet guidelines for early intervention are clinically feasible.

Test-retest reliability of wideband reflectance measures in infants under screening and diagnostic test conditions.

OBJECTIVE: The main goal of this study was to examine the test-retest reliability of wideband reflectance (WBR) measures collected from infants in screening and diagnostic hearing test environments. In addition, the results of WBR testing for infants who passed and failed otoacoustic emission (OAE) screening were examined to determine whether these measures distinguished between the two groups. DESIGN: Repeated WBR measures were collected from two groups of infants, one group tested in an outpatient hearing screening setting and the other group in a diagnostic test setting. For a total of 127 infants and a control group of 10 adults, repeated WBR measurements were made with the probe left in place between the two tests (T1 and T2) and after reinsertion of the probe (T3) for a total of 3 measurements. Test-retest differences were calculated for each individual across one-third octave frequency bands, and the mean and 90th percentile were calculated by subject group and OAE results. WBR patterns were also compared between infants who passed versus failed OAE screening. RESULTS: Mean test-retest differences were smaller for the diagnostic group than for the screening group. Test-retest differences were largest for the reinsertion condition and for the frequencies below 500 Hz. While the low frequencies were variable, the test-retest differences were smallest in the mid-frequency range which is thought to be the frequency range most sensitive to middle ear dysfunction. Test-retest performance did not differ between infants who passed or failed OAE screening. However, infants who failed OAE screening had significantly higher WBR in the range from 630 to 2000 Hz than infants who passed OAE screening. CONCLUSIONS: Test-retest performance was poor for frequencies below 500 Hz, but in general test-retest differences were small across the important mid-frequency range. Reinsertion of the probe between repeated tests yielded larger and more variable test-retest differences. Careful monitoring of probe fit and testing while infants are in a quiet state appears to be critical for obtaining reliable WBR results. Analysis of WBR results indicated significantly higher reflected energy in the mid-frequency range for infants who failed OAE screening than for those who passed OAE screening. Although conclusions are limited by the fact that the true status of the middle ear and cochlea were not known for the infants in this study, this result may indicate that a number of these infants failed OAE screening due to transient or permanent middle ear dysfunction which was detected by WBR.

Effect of audiometric configuration on threshold and suprathreshold auditory steady-state responses.

OBJECTIVE: The purpose of this study was to examine the correlation between auditory steady-state response (ASSR) thresholds and behavioral thresholds in hearing-impaired adults with two common audiometric configurations. A second goal was to compare suprathreshold ASSR growth functions in these two subject groups and to determine whether these growth functions could be used clinically to improve threshold estimation. DESIGN: Thirty adults participated, including 10 subjects with normal hearing, 10 subjects with flat moderately severe sensorineural hearing loss, and 10 subjects with sloping high-frequency sensorineural hearing loss. The accuracy of ASSR threshold estimations for the frequencies of 500, 1000, 2000, and 4000 Hz was compared across groups. In addition, ASSRs were recorded at multiple suprathreshold intensity levels, and the growth of the response was compared across subject groups. RESULTS: ASSR and behavioral thresholds were strongly correlated across all subjects, with no significant difference by audiometric configuration. Slightly poorer correlations were obtained in the normal-hearing subjects than in hearing-impaired subjects and for the 500-Hz test frequency compared with the higher stimulus frequencies. Subtraction and regression methods for predicting behavioral thresholds from ASSR thresholds were equally accurate. Suprathreshold amplitude growth was variable among individuals, but mean growth functions showed steeper slopes in hearing-impaired subjects than in normal-hearing subjects, particularly for the higher frequencies (2000 to 4000 Hz). However, there was not a significant difference in the slopes of amplitude growth functions between subjects with sloping versus flat audiometric configurations for these frequencies, and estimation of threshold from suprathreshold ASSR amplitude growth functions was not advantageous. CONCLUSIONS: ASSR thresholds accurately predicted behavioral threshold equally well for flat or sloping audiometric configurations. The accuracy of threshold estimation for either audiometric configuration and the similar growth function slopes may suggest that there is little spread of activation to neighboring regions of the cochlea when using multiple 100% AM stimuli in subjects with moderately sloping losses. The small amplitude of the ASSR response and individual variability may make threshold estimation based on extrapolation from suprathreshold ASSR responses impractical.

Estimating air-bone gaps using auditory steady-state responses.

Auditory steady-state responses (ASSR) were recorded using stimuli presented both via air conduction (AC ASSR) and bone conduction (BC ASSR) in 10 normal-hearing subjects with different degrees of simulated conductive hearing losses. The ASSR-estimated ABG (air-bone gap) was compared with the ABG measured using traditional pure-tone audiometric procedures. Reproducibility of the BC ASSR electrophysiological thresholds was also assessed. Additionally, a group of five subjects with profound sensorineural hearing loss was used to establish stimulation levels in which the BC ASSR was contaminated by stimulus artifact. Results of this investigation showed that the ASSR and behavioral ABGs were strongly correlated with each other (r = .81). However, ASSR-estimated ABGs slightly overestimated the magnitude of the behavioral. Reproducibility of the BC ASSR electrophysiological thresholds was good. Data from the five subjects with profound hearing loss, however, demonstrated that the levels where stimulus artifact became problematic were relatively low. This means BC stimulation may be appropriate only for subjects with normal or mildly impaired cochlear sensitivity.

Comparison of auditory steady-state response and auditory brainstem response thresholds in children.

Recently, auditory steady-state responses (ASSRs) have been proposed as an alternative to the auditory brainstem response (ABR) for threshold estimation. The goal of this study was to investigate the degree to which ASSR thresholds correlate with ABR thresholds for a group of sedated children with a range of hearing losses. Thirty-two children from the University of Iowa Hospitals and Clinics ranging in age from 2 months to 3 years and presenting with a range of ABR thresholds participated. Strong correlations were found between the 2000-Hz ASSR thresholds and click ABR thresholds (r = .96), the average of the 2000- and 4000-Hz ASSR thresholds and click ABR thresholds (r = .97), and the 500-Hz ASSR and 500-Hz toneburst ABR thresholds (r = .86). Additionally, it was possible to measure ASSR thresholds for several children with hearing loss that was great enough to result in no ABR at the limits of the equipment. The results of this study indicate that the ASSR may provide a reasonable alternative to the ABR for estimating audiometric thresholds in very young children.