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There is much evidence supporting the idea that pelagic larvae of coral reef fishes are active participants in their dispersal and return to a reef, however, the mechanisms used to navigate are still uncertain. It has been proposed that sensory cues, such as hearing, play a role. Sound is a potentially important cue for organisms in marine environments, especially in noisy environments like coral reefs. Sensory organs, including otolithic organs, of most coral reef fish form within the first few days of life. The auditory brainstem response (ABR) technique was used to measure hearing on a wide size range of sergeant majors (Abudefduf saxatilis). Complete audiograms were measured for 32 fish ranging in size from 11-121 mm. Significant effects of standard length on hearing thresholds at 100 and 200 Hz were detected. At these lower frequencies, thresholds increased with an increase in size. All fish were most sensitive to the lower frequencies (100-400 Hz). The frequency range that fish could detect sounds was dependent upon the size of the fish; the larger fish (>50mm) were more likely to respond to higher frequencies (1000-1600 Hz). A. saxatilis have poor hearing sensitivity in comparison to audiograms of other hearing generalists including other species of Pomacentrids. Due to the high hearing thresholds found in this study in comparison to recorded ambient reef noise, it is unlikely that sound plays a significant role in the navigation of the pelagic larvae of sergeant majors to the return of the reef from large distances.

Objective: The air conduction click is currently the most widespread stimulus used to estimate the pure tone audiogram as part of auditory brainstem response (ABR) testing. The click is characterized by its broad spectral content and rapid onset, which may not make it the best choice for frequency specificity. An alternative stimulus is a short duration tone burst stimuli with notched noise masking. When obtaining an ABR using standard unmasked tone bursts, the brief stimulus onset may cause spectral splatter producing response contributions from unwanted regions of the cochlea; thus reducing the frequency specificity of the ABR. Notched noise masking used in conjunction with the tone burst ABR, limits the evoked response to those frequencies within the notch, thereby reducing the likelihood of spectral splatter and increasing frequency specificity. The presence of a sloping sensory hearing impairment creates additional difficulties for achieving frequency specificity because of the likelihood that lower frequency cochlea regions, with less sensory damage, will contribute to the evoked response. It is theorized that notched noise masking will reduce the neural contributions from regions of the cochlear outside those within the notch, resulting in more frequency specific results than those achieved with a standard unmasked tone burst stimulus. The present study was designed to investigate the differences in Wave V latency between the notched noise ABR and the standard unmasked tone burst ABR as a measure of frequency specificity. Design: Twenty-five participants with normal hearing in at least one ear and 16 participants with bilateral SNHL participated in this investigation. Each participant was given an audiological evaluation, a click ABR screening to determine neural synchrony, a standard tone burst ABR and a notched noise tone burst ABR. Results: An Analysis of Variance (ANOVA) failed to reveal any significant Wave V latency differences between the ABRs obtained with unmasked tone bursts versus ABRs obtained with a notched noise tone burst. Conclusion: The results of this study do not support the use of notched noise tone bursts for improved ABR frequency specificity. This finding is contrary to previously reported results (Stapells & Picton, 1981), which indicated improved frequency specificity when obtaining a tone burst ABR in notched noise versus a standard unmasked tone burst ABR.

Professional research project (Au.D.)--University of South Florida, 2000. / Title from PDF of title page. / Document formatted into pages; contains 48 pages. / Includes bibliographical references. / Text (Electronic thesis) in PDF format. / ABSTRACT: The primary objective of the project was to survey recognized "experts" in the field of neurodiagnostic audiology and practicing audiologists regarding their referral criteria and referral patterns for administering an auditory brainstem response test (ABR). For purposes of this study, "expert" was defined as any recognized audiologist with at least two or more publications and/or seminarsin the field of auditory evoked potentials. / Responses of experts and practicing audiologists were compared and contrasted to establish: a) if there was a standard referral pattern; b) what, if any, were the apparent critical components of referral patterns; and, c) whether or not current practice reflected the utilization of such critical components. The survey was designed to establish whether the respondent was practicing, in what type of practice setting, and how often ABRs were performed. Specificity and sensitivity of ABR outcomes was also requested. / The survey was administered verbally, via telephone, to 3 experts and was sent via e-mail to 178 randomly selected audiologists in the United States. Of the latter 53 returned, 38 reported conducting ABRs. Thus, data analysis was reported on 38 respondents. The survey results did not reveal a consistent standard referral pattern. Critical components for referral were hypothesized based on the "expert" majority response. These include ABR referral based on the presence of: (1) asymmetric sensorineural hearing loss; (2) unilateral tinnitus; (3) positive reflex decay; and, (4) word recognition rollover. The majority of "non-expert" practitioners surveyed reported that these symptoms warranted consideration for referral, thus reflecting utilization of apparent critical components. / System requirements: World Wide Web browser and PDF reader. / Mode of access: World Wide Web.

Auditory evoked potentials (AEPs) have become commonly used to measure hearing thresholds in fish. However, it is uncertain how well AEP thresholds match behavioral hearing thresholds and what effect variability in electrode placement and tank composition has on AEPs. In the first experiment, the effect of testing tank composition and electrode placement on AEPs was determined by recording AEPs in the same individual fish in a steel and PVC cylindrical testing tank, and simultaneously recording AEPs from four locations and two different depths on each of 12 goldfish, Carassius auratus. Results from these studies show that tank composition has an effect AEP strength and hearing thresholds, with steel producing lower thresholds for all frequencies. Electrode placement and depth showed no significant effect on hearing thresholds.In the second experiment, the hearing sensitivity of 12 goldfish was measured using both classical conditioning and AEPs in the same setup. For behavioral conditioning, the fish were trained to reduce their respiration rate in response to a 5s sound paired with a brief shock. Once the behavioral audiogram was completed, the AEP measurements were made without moving the fish. The same sound stimuli were presented and the resultant evoked potentials were recorded for 1,000-6,000 averages. AEP input-output functions were then compared to the behavioral audiogram to compare techniques for estimating behavioral thresholds from AEP data. Results show a large range in variability between behavioral and evoked potential thresholds between fish, with the linear regression evoked potential analysis method producing closer thresholds to behavioral methods. In the third study, the effects of masking were examined on the behavioral and evoked potential audiograms. Behavioral thresholds were first determined with a constant masking noise for two frequencies, followed by threshold measurements with no masking noise.

The objective of this study is to investigate automatic recognition of speech-evoked auditory brainstem responses (speech-evoked ABR) to the five English vowels (/a/, /ae/, /ao (ɔ)/, /i/ and /u/). We used different automatic speech recognition methods to discriminate between the responses to the vowels. The best recognition result was obtained by applying principal component analysis (PCA) on the amplitudes of the first ten harmonic components of the envelope following response (based on spectral components at fundamental frequency and its harmonics) and of the frequency following response (based on spectral components in first formant region) and combining these two feature sets. With this combined feature set used as input to an artificial neural network, a recognition accuracy of 83.8% was achieved. This study could be extended to more complex stimuli to improve assessment of the auditory system for speech communication in hearing impaired individuals, and potentially help in the objective fitting of hearing aids.

The objective of this thesis is to characterize and identify the representation of four short English vowels in the frequency following response (FFR) of 22 normal-hearing adult subjects. The results of two studies are presented, with some analysis. The result of the first study indicates how the FFR signal of four short vowels can be used to identity different subjects. Meanwhile, a rigorous test was conducted to test and verify the quality and consistency of responses from each subject between test and retest, in order to provide strong and representative features for subject identification. The second study utilized machine learning and deep learning classification algorithms to exploit features extracted from the FFRs, in both time and frequency domains, to accurately identify subjects from their responses. We used three kinds of classifiers with respect to three aspects of the features, yielding a highest classification accuracy of 86.36%. The results of the studies provide positive and important implications for establishing a biometric authentication system using speech-evoked FFRs.

Objective: The aim of this study was to compare cervical and ocular vestibular evoked myogenic potentials (cVEMP and oVEMP) in young gender- and age-matched black African and Caucasian male and female adults. Design: A quasi-experimental between-subjects research design was utilised. This study was comparative in nature, thus data was collected in a cross-sectional manner from two age- and gender-matched racial groups, namely black African and Caucasian, and compared. Furthermore, interactions of gender and race were also examined in this research study. Methods: Sixty healthy age- and gender-matched participants (30 black African, 30 Caucasian) between the ages of 18 25 years participated in this study. Fifteen males and fifteen females, within one year of the age of their racial participant counterparts, were included in each racial group. Latencies, peak-to-peak amplitudes and asymmetry ratios were analysed for both groups in these tests. Furthermore, auditory brainstem response (ABR) and electromyography (EMG) testing were conducted to investigate whether possible racial differences in VEMP tests could be attributed to differences in neural or muscular function. Results: Black African participants demonstrated significantly shorter latencies of the n23 component of the cVEMP and the p15 component of the oVEMP, as well as larger peakto- peak amplitude of the oVEMP response. Highly significant differences were found in all EMG measurements between the two racial groups, suggesting that these racial VEMP differences are primarily based on differences in muscular function between black Africans and Caucasians. Significant gender differences were observed in all tests conducted, with females predominantly displaying shorter latencies, while males had larger amplitudes. Conclusions: Young black African adults demonstrated significant differences in both cVEMP and oVEMP responses, namely shorter latencies and larger amplitudes, in comparison to young Caucasian adults. Correlations with differences in EMG measurements suggest that these differences are primarily due to differences in muscular function as opposed to neural function. Future research is required to confirm and expand on these findings. / Dissertation (MCommunication Pathology)--University of Pretoria, 2016. / Speech-Language Pathology and Audiology / MCommunication Pathology / Unrestricted

The purpose of this study was to determine the prevalence of the binaural interaction component (BIC) in a large sample of normal hearing adults, and to measure the absolute latency and amplitude of the BIC as a function of the click rate of the stimulus and the electrode montage. The BIC is obtained by subtracting the auditory evoked potential waveform obtained with binaural stimulation from the waveform obtained by adding the responses from the left and right monaural stimulation. The tested hypothesis was that the recordings of the BIC vary among normal hearing individuals, and BIC latency and amplitude values change as a function of stimulus rate. Studies of the BIC help to explain the neural correlates of some binaural processes, and to develop an electrophysiological index of binaural processes for objective clinical evaluations. Data was completed and analyzed on 47 adults between the ages of 20 and 41 (mean = 25) with hearing in the normal range (thresholds less than or equal to 20 dB HL at 500, 1000, 2000, and 4000 Hz in each ear) and no known neurological disorders. The results revealed a great variability in BIC morphology between subjects. The BIC waveforms were categorized into five distinct groups according to the number of positive and negative peaks present. Chi-square analyses revealed a significant relationship between click rate and BIC category; however, the relationship between recording montage and BIC category was insignificant. An Analysis of Variance (ANOVAs) revealed a significant increase in absolute latency and decrease in absolute amplitude of both negative and positive peaks as click rate increased from 7.7/s to 57.7/s. The results did not reveal a significant change in the type of BIC as an effect of electrode montage. In conclusion, the BIC within the binaural difference waveform may be obtained in the majority of young individuals with normal hearing. Specifically, a slower stimulus rate revealed more components of the waveform, as well as an improvement in the morphology of the BIC compared to a faster stimulus rate. As these findings may aid in the development of an electrophysiological index of binaural neural processes in young individuals with normal hearing, more research should be attempted in the study of BIC in other age groups and patients with different audiograms.

Hearing loss of various types is increasingly plaguing our modern world (Geneva: World Health Organization 2018). As the life expectancy increased in the industrialized world, age-related hearing loss (ARHL) has become more prevalent. The wars and terrorism of the modern world also created a significant body of blast-induced hearing loss (BIHL) patients. Both types of hearing loss present significant challenges for listeners even at suprathreshold sound levels. However, increasing bodies of clinical and laboratory evidence have suggested that the difficulties in the processing of time-varying auditory features in speech and other natural sounds may not be sufficiently diagnosed by threshold changes and simple auditory electrophysiological measures (Snell and Frisina 2000; Saunders et al. 2015; Bressler et al. 2017; Guest et al. 2018).<br>Studies have emphasized that excitatory/inhibitory neurotransmission imbalance plays important roles in ARHL (Caspary et al. 2008) and may also be key in BIHL, as hinted by the strong presence of GABA regulation in non-blast TBI (O’Dell et al. 2000; Cantu et al. 2015; Guerriero et al. 2015). The current studies focus on age-related and blast-induced hearing deficits by examining changes in the processing of simple, brief stimuli and complex, sustained, temporally modulated sounds.<br>Through post hoc circular analysis of single-unit, in vivo recording of young and aged inferior colliculus (IC) neurons responding to amplitude modulation (AM) stimuli and modulation depth changes, we observed evidence of central compensation in the IC manifesting as increased sensitivity to presynaptic input, which was measured via local field potentials (LFPs). We also found decreased sensitivity to decreasing modulation depth. Age-related central gain in the IC single units, while preserving and even overcompensating for temporal phase coding in the form of vector strength, was unable to make up for the loss of envelope shape coding.<br>Through careful, longitudinal measurements of auditory evoked potential (AEP) responses towards simple sounds, AM and speech-like iterated rippled noise (IRN), we documented the development and recovery of BIHL induced by a single mild blast in a previously established (Song et al. 2015; Walls et al. 2016; Race et al. 2017) rat blast model over the course of two months. We identified crucial acute (day 1-4 post-exposure) and early recovery (day 7-14) time windows in which drastic changes in electrophysiology take place. Challenging conditions and broadband, speech-like stimuli can better elucidate mild bTBI-induced auditory deficits during the sub-acute period. The anatomical significance of the aforementioned time windows was demonstrated with immunohistochemistry methods, showing two distinct waves of GABA inhibitory transmission changes taking place in the auditory brainstem, the IC, and the auditory thalamus. These changes were in addition to axonal and oxidative damage evident in the acute phase. We examined the roles and patterns of excitatory/inhibitory imbalance in BIHL, its distinction compared to that of ARHL, and demonstrated the complexity of its electrophysiological consequences. Blast traumatizes the peripheral auditory system and auditory brainstem, evident through membrane damage and acrolein-mediated oxidative stress. These initial traumas kickstart a unique, interlocking cascade of excitatory/inhibitory imbalances along the auditory neuraxis that is more complex and individually varied than the gradual, non-traumatic degradations in ARHL. Systemic treatment with the FDA-approved acrolein scavenger Hydralazine (HZ) was attempted with limited effects.<br>Taken together, the current study provided insights into the similarities and distinctions between the mechanisms of ARHL and BIHL and called for innovative and individual diagnostic and therapeutic measures.<br>