UBC Theses and Dissertations
The effect of noise floor on cortical auditory evoked potential response detection at threshold intensities Ritchie, Heather
Cortical auditory evoked potentials (CAEPs) are neural responses that occur in response to changes in sound, which can be recorded from electrodes placed on the scalp. The N1-P2 response can be reliably used to determine a person’s frequency-specific hearing thresholds. This objective method for hearing assessment is used clinically in situations where the patient is unable or unwilling to provide reliable behavioural responses. Currently, the gold standard method of interpreting CAEP results is dependent upon the visual judgment of the clinician. A high level of noise in the recordings may obscure a small N1-P2 response. Established criteria for an acceptable residual noise (RN) level does not currently exist. Such criteria could be used as a tool to assist in the interpretation of CAEPs, making judgments more reliable among clinicians. The goal of the present study was to estimate a noise criterion based on recorded and simulated CAEP averages with various different levels of RN. CAEP results at threshold and sub-threshold intensities were recorded for 12 normal hearing adults at 500 Hz and 2000 Hz. Each waveform was presented a total of five times, with each average including a different number of sweeps. Simulated CAEPs were generated (N=37), with averages including a variety of different RN levels. The waveforms were presented to three expert raters, who judged each waveform independently as having an N1-P2 response present or absent. RN criterion, maximal noise floor allowable for judging a response as truly absent, was determined when raters performed at 95% sensitivity of detecting a true response. The recommended criteria for the maximum noise floor level were 0.111 μV (relative to the pre-stimulus interval) or 0.145 μV (relative to the post-stimulus interval). Simulated data exhibited a better face validity than the recorded CAEPs. Further studies may lead to the implementation of new guidelines surrounding RN criteria in CAEP recording procedures. Such guidelines may provide more validity and reliability in clinical practice.
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