The middle ear system is a vital component in the propagation mechanism of otoacoustic emissions. As such, investigation of the effect of variation in middle ear impedance on the measurement of emissions is warranted. Distortion product otoacoustic emissions (DPOAEs) have gained recognition as a means of gaining frequency specific information on auditory function. As the effects of changes in middle ear impedance will vary as a function of frequency, a clear definition of the relationship between middle ear impedance and DPOAE amplitude across the frequency spectrum is needed. Twenty adults (ages 20-37) with normal hearing and normal middle ear function were selected as subjects. Commercially available equipment (Virtual 330) was used to measure the DPOAEs on all subjects. The unit was modified to change canal pressure by coupling the probe to the pressure pump of a clinical acoustic immittance system. One ear from each subject was randomly selected for measurement and each subject was tested under five pressure conditions: +200, O, -200, -300, -400 daPa. The mean frequency of the fl/f2 tone pairs swept from 500 to 8000 Hz. Results indicate that changes in ear canal pressure can effect the amplitude of DPOAEs. Alteration of ear canal pressure resulted in decreased emission amplitude. This effect was found to differ as a function of eliciting frequency with the greatest reduction in amplitude with the mean of the primaries at 500 Hz. Less variation was noted across the ear canal pressures with the higher frequency stimuli. These results are consistent with previous findings reported regarding the effects of impedance changes on spontaneous and transiently evoked otoacoustic emissions.

This article summarizes the significant contributions of Fred H. Bess to the early detection of hearing loss in infants and children. Based on public health and educational policy, Bess challenged audiologists to view hearing screening as a responsibility that brought with it the need to develop screening tools that are effective in identifying hearing loss - whether for use with infants, preschoolers, or school-age children - and that adhere to important screening principles. A review of his influence on pertinent guidelines, position statements, and recommendations highlights his belief that early identification of hearing loss is critical if children are to overcome the significant obstacles presented by even mild and unilateral hearing losses. This section is followed by a review of seminal papers that stimulated research in universal newborn hearing screening programs and the detection of unilateral and minimal hearing loss. We conclude with a review of selected studies that build on Bess's earlier work and strive to drive our field forward to practices that are both evidence-based and effective in detecting hearing loss in children.