Preliminary studies have stirred the hope that sound-field stimulation through auditory steady state evoked potentials can be used to assess aided thresholds in the difficult-to-test population. Before the introduction of ASSEP into the clinical field, as a technique for the prediction of aided thresholds in the difficult-to-test population, a question arises concerning its clinical validation. The application of ASSEP through sound field stimulation, in the determination of aided thresholds and for the evaluation of amplification fittings, is dependent on the determination of unaided responses. Subsequently the estimation of unaided thresholds in the hearing impaired population is dependent on the establishment of normative data from the normal hearing population. The aim of this study was to determine the influence of insert earphones and sound field speaker presentation on threshold estimations using monotic auditory steady state evoked potentials, in a group of normal hearing adults. To achieve the aim of the study, a comparative, within-group experimental design was selected. The results of the current study indicated that the monotic single ASSEP technique under both insert earphone- and sound field conditions provided a reasonable estimation (25-35 dB HL for inset earphones; 20-33 dB HL for sound field speaker presentation) of the behavioural pure tone thresholds. The minimum response levels obtained under insert earphone conditions differed significantly from those obtained under sound field conditions for all the frequencies tested except 2 kHz (p < 0.01). Subsequently, the current study indicates that minimum response levels obtained using a specific transducer should serve as the basis of comparison with behavioural thresholds obtained under the same transducer. Therefore, behavioural pure tone thresholds obtained under insert earphone conditions will not suffice as a basis of comparison for minimum response levels obtained for the ASSEP technique under sound field conditions, and vice versa. This research endeavour concluded that the monotic ASSEP technique under both insert earphone and sound field conditions provide useful information for the estimation of frequency specific thresholds, but that the results are transducer specific and that comparison across transducers should be avoided. / Dissertation (M (Communication Pathology))--University of Pretoria, 2006. / Speech-Language Pathology and Audiology / Unrestricted

Determining auditory functioning in difficult-to-test populations such as cerebral palsy (CP) remains a challenge in paediatric audiology. The auditory brainstem response (ABR) is favoured as the procedure to assess auditory functioning in difficult-to-test populations such as CP. The CP population, however, offers unique challenges for the ABR procedure due to the presence of involuntary muscular movements that may compromise the signal-to-noise ratio (SNR) of the ABR. Conventional ABR technology attempts to improve the SNR by the modification of acquisition parameters e.g. adjusting the low cut filter or implementing stricter artifact rejection criteria. However, such modifications may compromise the waveform morphology of the ABR. Furthermore, sedation or general anesthesia can also be used to improve the SNR by reducing excessive muscular movements. The CP population, however, displays a high risk for developing upper airway obstruction when being sedated or anesthetized. Thus, the feasibility and reliability of the conventional ABR may be compromised when being employed in the CP population. In recent years a novel ABR system, the Vivosonic Integrity (VS) ABR has become clinically available. The device incorporates features such as pre-amplification of the ABR signal, Kalman filtering and wireless recording. These features promise to address the limitations of conventional ABR technology to obtain a reliable recording in the midst of excessive myogenic artifact. The aim of this study was therefore to evaluate the clinical utility of the VS system when assessing a sample of children with CP without the use of sedation. The clinical utility of the VS ABR system was determined by comparing its success rates, the threshold correspondence to behavioural pure tone (PT) thresholds and recording time to a conventional ABR system when using click and 0.5 kHz TB stimuli. A cross-sectional within-subject comparison research design was selected in order to compare thresholds obtained with different procedures. The experimental part of this study was represented by the within-subject control condition where the VS ABR system and the conventional ABR system were simultaneously conducted in each subject. This unique setup was important in the research as equivalent test conditions in terms of EEG and environmental conditions had to be ensured for both ABR systems. 15 CP subjects between the ages of 12 and 18 years were included in the project. A diagnostic audiological test battery including immittance, distortion product otoacoustic emissions and behavioural audiometry was conducted on each subject prior the administration of the ABR procedures. The variability of the audiological test battery results – between the subjects and when compared to previous research – emphasized the heterogeneity of the CP population. Furthermore, more than half of the research sample (53%; n=15) responded inconsistently to behavioural pure tone (PT) stimuli. It was suggested that the severity of physical impairments as well as additional impairments such as mental retardation might have influenced the consistency of the subjects’ responses during behavioural PT audiometry. The ABR results indicated that there were no significant differences with regards to threshold correspondence and recording time between the two ABR systems when using click and 0.5 kHz TB stimuli (p>0.05). With regards to the success rates, the VS system was successful in more cases than the conventional ABR system using click and 0.5 kHz TB stimuli. Although results also showed no statistically significant value for click p=.1121) and 0.5 kHz TB stimuli p=.1648), there was a tendency towards the 95% confidence level in both cases suggesting that the VS ABR system may produce a statistically significant success rate for click as well as for 0.5 kHz TB stimuli, provided a larger sample is tested. The research indicated that, since the VS ABR system was more successful across a wider range of subjects during click-evoked and 0.5 kHz TB recordings, it may increase the clinical usefulness of the ABR especially in terms of hearing screening in the CP population. The research suggested that excessive muscular movements during the recordings influenced not only the VS ABR’s, but also the conventional ABR’s threshold correspondences to PT thresholds as well as the recording time of the measurements. Therefore it may still be necessary to use a light sedative in some CP patients to reduce excessive myogenic interference despite the possible advantages of the VS ABR system. / Dissertation (MCommunication Pathology)--University of Pretoria, 2010. / Speech-Language Pathology and Audiology / unrestricted