The effect of noise levels on transient evoked otoacoustic emissions (TEOAE) measures

A systematic investigation of the effect of environmental noise on transient evoked otoacoustic emissions (TEOAE) measures was completed using the ILO 88 Otodynamics Analyzer with the Quickscreen option. Dependent variables included whole and bandlimited reprodudbility measures.^ Repeated TEOAEs were collected on 26 adult subjects using four different noise types: white noise, broadband noise, one octave wide 500 Hz narrowband noise, and one octave wide 2000 Hz narrowband noise. Each noise was presented at eight intensity levels from 45 dBA to 75 dBA in 5 dB increments.^ Repeated measures analysis of variance results showed no significant effect of intensity level until 55 dBA to 65 dBA dependent on noise type used and reproducibility measure investigated.^ Narrowband noises had their greatest effect on the bandlimited reproducibilities which had similar frequency content. The one octave wide narrowband noise centered at 500 Hz affected whole reproducibility only. It did not affect any of the bandlimited reproducibilities presumably because its narrow frequency range did not spread energy into the bandlimited frequency bands.^ Ten infants were tested with a reduced set of criteria based on adult results. Infants were tested at levels beginning at 40 dBA. Testing continued at higher intensity levels until an acceptable TEOAE could not be obtained.^ Comparing infant to adult results using t-tests for the intensity range of 45 to 55 dBA, infants had significantly poorer 1600 Hz reproducibility scores with all noises, but significantly better 3200 Hz and 4000 Hz reproducibility scores with the narrowband noises. The greater noise generated by infants in the low frequencies and the greater emission amplitude of infants in the high frequencies are suspected to be responsible, in part, for this finding.^ It was noted that high levels of noise caused a state change in infants, arousing them into a state unsuitable for testing.^ Results suggest that for newborn hearing screening the criteria used to determine acceptable TEOAEs need to take into account level and frequency content of environmental noise present during testing.