Tone burst evoked otoacoustic emissions in different age-groups of schoolchildren

IntroductionOtoacoustic emissions (OAEs) are believed to be good predictors of hearing status, particularly in the 1–4 kHz range. However both click evoked OAEs (CEOAEs) and distortion product OAEs (DPOAEs) perform poorly at 0.5 kHz. The present study investigates OAEs in the lower frequency range of 0.5–1 kHz evoked by 0.5 kHz tone bursts (TBOAEs) in schoolchildren and compares them with emissions evoked by clicks.MethodsMeasurements were performed for two groups of normally hearing schoolchildren. Children from 1st grade (age 6–7 years) and children from 6th grade (age 11–12 years). Tympanometry, pure tone audiometry, and OAE measurements of CEAOEs, 0.5 kHz TBOAEs, and spontaneous OAEs (SOAEs) were performed. Additionally, analysis by the matching pursuit method was conducted on CEOAEs and TBOAEs to assess their time–frequency (TF) properties.ResultsFor all subjects OAEs response levels and signal to noise ratios (SNRs) were calculated. As expected, CEOAE magnitudes were greatest over the range 1–4 kHz, with a substantial decrease below 1 kHz. Responses from the 0.5 kHz TBOAEs were complementary in that the main components occurred between 0.5 and 1.4 kHz. In younger children, TBOAEs had SNRs 4–8 dB smaller in the 0.5–1.4 kHz range. In addition, CEOAEs had lower SNRs in the 0.7–1.4 kHz range, by 3–5 dB. TBOAEs in younger children had maximum SNRs shifted toward 1–1.4 kHz, whereas in older children it was more clearly around 1 kHz. The differences in response levels were less evident. The presence of SOAEs appreciably influenced both CEOAEs and TBOAEs, and TF properties of both OAEs did not differ significantly between grades.ConclusionTBOAEs evoked at 0.5 kHz can provide additional information about frequencies below 1 kHz, a range over which CEOAEs usually have very low amplitudes. The main difference between the two age groups was that in older children CEOAEs and 0.5 kHz TBOAEs had higher SNRs at 0.5–1.4 kHz. Additionally, for ears with SOAEs, 0.5 kHz TBOAEs had higher response levels and SNRs similar to CEOAEs.