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Behavioural bone-conduction responses of infants 7-30 months of age to warbled-tone stimuli Hulecki, Lauren Rachel

Abstract

The purpose of the present study is to obtain behavioural bone-conduction thresholds of infants 7-15 and 18-30 months of age using a clinical visual reinforcement audiometry (VRA) protocol to determine whether frequency-dependent patterns exist. Assessment of boneconduction hearing is an essential component of an audiological test battery because it provides the information necessary to differentiate between sensorineural, conductive and mixed hearing losses. Many studies investigated the maturation of air- and/or bone-conduction thresholds in infants using objective physiological measures, such as the auditory brainstem response (ABR) and the auditory steady-state response (ASSR), reporting infant-adult differences in air- and bone-conduction hearing sensitivities. Also, frequency-dependent differences have been reported where air-conduction thresholds are better in the high- compared to low-frequencies while boneconduction thresholds are better in the low- compared to high-frequencies. These differences reveal a low-frequency “maturational” air-bone gap, which reflects a stimulus calibration issue rather than a conductive pathology. Only one published study has reported behavioural boneconduction thresholds for infants (Gravel, 1989). However, maturational changes in boneconduction hearing sensitivity have not been directly investigated using behavioural methods. The present study behaviourally assesses bone-conduction thresholds across frequency (500, 1000, 2000 and 4000 Hz) using a clinical VRA protocol for normal-hearing infants 7-15 and 18- 30 months of age. It is hypothesized that the frequency-dependent differences identified for infants using objective techniques will be comparable to the results obtained behaviourally. Therefore, it is expected that all infants tested will have better low- compared to high-frequency thresholds which will become more adult-like with age. Results of this study indicated that, when measured behaviourally, infant’s show frequency-dependent bone-conduction thresholds where their responses at 500 and 1000 Hz are significantly better than those at 2000 and 4000 Hz. Compared to previously documented air-conduction thresholds of infants using similar VRA techniques, there is a difference between air- and bone-conduction thresholds in the low frequencies. However, thresholds obtained from the younger group of infants (mean age of I 0.6 months) were not significantly different from those obtained from the older group of infants (mean age of 23.0 months) at any frequency, suggesting minimal maturational changes in bone conduction hearing sensitivity between these groups.

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