This thesis is concerned with the study on the effect of the swimbbadder on hearing sensitivity in Ameiurus nebulosus nebulosus. The investigation has been performed by means of auditory threshold curves in normal catfish and in catfish in which the resonance of the swim­bladder was eliminated, The results were compared. The thesis consists of an introduction to the investigation, followed by a review of the literature in relation to the problem, a description of the material and technique and of the experimental work, the results obtained with a discussion and a summary. / Thesis / Master of Science (MS)

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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.

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Background: Hearing loss and age interfere with the auditory system's ability to process temporal changes in the acoustic signal. A key unresolved question is whether high-frequency sensorineural hearing loss (HFSNHL) affects temporal processing in the low-frequency region where hearing loss is minimal or nonexistent. A second unresolved question is whether changes in hearing occur in middle-aged subjects in the absence of HFSNHL. Purpose: The purpose of this study was twofold: (1) to examine the influence of HFSNHL and aging on the auditory temporal processing abilities of low-frequency auditory channels with normal hearing sensitivity and (2) to examine the relations among gap detection measures, self-assessment reports of understanding speech, and functional measures of speech perception in middle-aged individuals with and without HFSNHL. Research Design: The subject groups were matched for either age (middle age) or pure-tone sensitivity (with or without hearing loss) to study the effects of age and HFSNHL on behavioral and functional measures of temporal processing and word recognition performance. These effects were analyzed by individual repeated-measures analyses of variance. Post hoc analyses were performed for each significant main effect and interaction. The relationships among the measures were analyzed with Pearson correlations. Study Sample: Eleven normal-hearing young adults (YNH), eight normal-hearing middle-aged adults (MANH), and nine middle-aged adults with HFSNHL were recruited for this study. Normal hearing sensitivity was defined as pure-tone thresholds ≤25 dB HL for octave frequencies from 250 to 8000 Hz. HFSNHL was defined as pure-tone thresholds ≤25 dB HL from 250 to 2000 Hz and ≥35 dB HL from 3000 to 8000 Hz. Data Collection and Analysis: Gap detection thresholds (GDTs) were measured under within-channel and between-channel conditions with the stimulus spectrum limited to regions of normal hearing sensitivity for the HFSNHL group (i.e., <2000 >Hz). Self-perceived hearing problems were measured by a questionnaire (Abbreviated Profile of Hearing Aid Benefit), and word recognition performance was assessed under four conditions: quiet and babble, with and without low-pass filtering (cutoff frequency = 2000 Hz). Results: The effects of HFSNHL and age were found for gap detection, self-perceived hearing problems, and word recognition in noise. The presence of HFSNHL significantly increased GDTs for stimuli presented in regions of normal pure-tone sensitivity. In addition, middle-aged subjects with normal hearing sensitivity reported significantly more problems hearing in background noise than the young normal-hearing subjects. Significant relationships between self-report measures of hearing ability in background noise and word recognition in babble were found. Conclusions: The conclusions from the present study are twofold: (1) HFSNHL may have an off-channel impact on auditory temporal processing, and (2) presenescent changes in the auditory system of MANH subjects increased self-perceived problems hearing in background noise and decreased functional performance in background noise compared with YNH subjects.

Abstract is available through the XX IERASG Biennial Symposium.

The relationship between hearing sensitivity in the extended high-frequency region (8-16 kHz) and (1) the presence of synchronized spontaneous otoacoustic emissions (SSOAEs) and (2) the strength of click-evoked and distortion product otoacoustic emissions (CEOAEs and DPOAEs) was investigated in 104 ears of 57 young adults. The age range was confined to 16 to 19 years. All subjects had normal hearing in the conventional audiometric frequency range (0.5-8 kHz). Ears with detected SSOAEs had better hearing sensitivity in the extended high-frequency region and also higher levels of CEOAEs and DPOAEs than ears with undetected SSOAEs. The results support the hypothesis that the presence of SSOAEs is indicative of an ear with highly normal cochlear function over a broad frequency range.