The purpose of this investigation was (1) to perform hearing screening tests on 100 youths who are classified as delinquent; (2) to evaluate more completely the hearing of those who fail the hearing screening tests in order to determine the nature and severity of the losses; and (3) to determine whether or not any significant number of the youths tested demonstrate nonorganic components in their reported audiometric thresholds.

The Stenger Principle describes the observation that when two tones of the same frequency are presented simultaneously, a single tone is perceived only in the ear in which the tone is louder. This principle underlies the Stenger Test, which is used to identify the presence of unilateral nonorganic hearing loss (NOHL). Minimum contralateral interference levels (MCILs), which can be used to estimate true hearing thresholds in individuals with unilateral NOHL, are also based on this principle. In this study, the Stenger Principle is used to examine MCILs and the correspondence of the MCILs to true hearing thresholds in 16 adults with normal hearing. In Part I of the study, subjects were asked to feign a unilateral hearing loss. Average MCILs were 12.5, 15.1, and 13.5 dB HL for 1.0, 2.0, and 4.0 kHz, respectively. These were obtained with nearly equal interaural stimulus levels. The average difference between MCIL and true hearing threshold was 7.6, 9.7, and 8.9 dB, respectively. In Part II of this study, subjects were asked to make lateralization judgments for simultaneously presented tones with varying interaural intensity differences. Individual subject ratings were compared to MCILs obtained in Part I. Although most subjects showed the Stenger Effect with a midline percept of the two tones, variability between subjects existed. In some cases the Stenger Effect was not apparent until the tonal image was pulled nearly to the "poor" ear. Because of the potential differences in response bias (a client may show the Stenger Effect with a small shift in the tonal signal away from the "good" ear or may require the tonal signal to be fully lateralized to the "poor" ear), clinicians cannot predict exact hearing thresholds. Rather, it is useful to describe a range within which the true threshold will be. The 90% ranges (5th and 95th percentiles) calculated in this study were approximately 1 and 17 dB. That is, the MCILs for the majority of the subjects were within ~ 1 and 17 dB of true hearing thresholds.

In individuals claiming compensation for occupational noise induced hearing loss, a population with a high incidence of nonorganic hearing loss, a reliable and valid behavioural pure tone (PT) threshold is not always achievable. Recent studies have compared the accuracy of behavioural PT threshold estimation using the slow cortical auditory evoked potentials (SCAEP) and auditory steady-state responses (ASSR) but there is no consensus regarding recommended technique. A review of the literature indicated that no comparison has been completed on the use of SCAEP and a single frequency ASSR technique. A research project was therefore initiated with the aim of comparing the clinical effectiveness (accuracy) and clinical efficiency (time required) of SCAEP and ASSR for behavioural PT threshold estimation in adults exposed to occupational noise. Adult participants were divided into a group with normal hearing (behavioural PT thresholds < 20 dBHL; n = 15) and a group of participants with hearing loss (n = 16 adults), the latter of which were recruited from individuals referred for audiometric screening, as part of hearing conservation programs, and who were, therefore, exposed to occupational noise. The GSI Audera electrophysiological system was used for both SCAEP and ASSR threshold measurement at 0.5, 1, 2 and 4 kHz. Use was made of tone burst stimuli for the SCAEP (rise and fall of 10 ms with 80 ms plateau), while amplitude and frequency modulated (AM/FM) stimuli was used during ASSR testing. The system’s 40 Hz protocol was chosen for use during ASSR recording while participants slept because this led to lparticipants. ASSR thresholds could not be measured in two of the three sleeping participants in the preliminary study using an 80 Hz modulation rate due to excessive noise. The mean SCAEP difference scores (SCAEP threshold minus behavioural PT threshold) for both participant groups were -0.2+10.2, 2.8+10.1,5.8+9.7, 0.5+10.4 at 0.5, 1, 2, and 4 kHz respectively, while ASSR difference scores were 25.3+12.8, 21.7+11.3,32.3+12.2, 27.1+13.8. The SCAEP correlations with behavioural PT thresholds across frequencies (r = 0.85) were also stronger than ASSR correlations (r = 0.75). Therefore, with regard to proximity of auditory evoked potentials (AEP) to behavioural PT thresholds and consistency of this relationship, the SCAEP, rather than ASSR, is the AEP of choice. However, the SCAEP took on average 10.1 minutes longer to complete than the ASSR. Clinical effectiveness was given comparably more weight than the clinical efficiency of the AEP technique to estimate behavioural PT thresholds due to the impact on overcompensation for occupational noise induced hearing loss. As such, the study acknowledged the SCAEP as the AEP of choice for the purpose of behavioural PT thresholds in adults exposed to occupational noise. It is important to note that the conclusion reached in the current study arose from the comparison of the SCAEP with a specific ASSR technique. Accuracy of ASSR estimation of behavioural PT thresholds is strongly influenced by stimulus and recording parameters of the system used, and by the participant variables. Copyright / Dissertation (MCommunication Pathology)--University of Pretoria, 2010. / Speech-Language Pathology and Audiology / Unrestricted