The fly

These first Snapshots of 2002 encourage readers to seek out two articles published in journals outside the familiar realm of audiology. One of these articles, in the April 2001 issue of Nature, discusses the directional hearing ability of the Ormia fly. The second article, in the November 2001 of Pediatrics, offers surprising insights into mothers' reactions to their infants' failures on newborn hearing screening.FigureTHE REMARKABLE ORMIA In their study, “Hyperacute directional hearing in a microscale auditory system,” Andrew Mason of the University of Toronto at Scarborough, Michael Oshinsky of Thomas Jefferson University, and Ron Hoy of Cornell University describe the remarkable sound-localization abilities of the Ormia ochracea fly. While most flies exhibit no sense of hearing, the Ormia is capable of pinpointing the direction of a sound source with an extraordinary degree of precision. Since the Ormia measures less than 1 cm in length, the distance between its two ears is tiny (0.5 mm), creating a situation in which directional hearing would appear to be anatomically impossible. Localization of sound normally occurs as a result of the interpretation of meaningful interaural intensity and time cues. Mason et al. sought to measure the sound-localization ability of the Ormia. Female Ormia were fixed on a spherical treadmill. Simulated cricket chirps were delivered via a movable speaker that could deliver stimuli in 0.5-degree increments through 40 degrees on either side of the mid-line axis. The simulated cricket chirp elicited a walking response from the fly, resulting in rotation of the spherical treadmill. The researchers found that the Ormia reliably turned and walked in the precise direction of the simulated cricket chirp. Despite its miniscule size, the Ormia was able to localize sound sources within 2 degrees azimuth, a precision equal to that of humans. The research described by the authors is quite fascinating, particularly in view of its potential implications for development of directional-microphone technology based on the Ormia's ears. The localization capabilities of the Ormia are mediated by a pair of tympani (eardrums) that are connected via a thick, cuticular structure. This arrangement enables the peripheral auditory system of the Ormia to detect tiny interaural intensity and time difference cues and mechanically amplify the information into cues that its rudimentary nervous system can interpret. Several industrial and engineering labs in the U.S are seeking to develop miniature listening devices based on the anatomical design of the Ormian ear. It is hoped that this work may eventually lead to the creation of smaller, cheaper, and more accurate directional hearing aid microphones. WHEN BABIES FAIL THE HEARING SCREEN Over the past several years, the widespread implementation of a two-tiered universal newborn screening system in which infants are initially screened (stage 1) and, those that fail re-screened (stage 2), has turned the focus of the medical community to various potential issues related to the screening process. Viktor Weichbold and Kunigunde Welzl-Mueller of the Innsbruck (Austria) University Hospital assessed the influence of false-positive screening results on overall maternal concern at two points: (1) immediately after the infant failed the first stage screening, and (2) immediately after the infant failed the second stage re-screening. Over a 1-year period, two separate groups of new mothers whose infants failed the first and/or second stage of screening were anonymously questioned regarding their level of concern about their child's screening test results. Of the 85 new mothers who completed the questionnaire, 34 (40%) were unaware that their infant had failed the first stage of the screening. Of the remaining 51 mothers, an overwhelming majority expressed either no concern (59%) or only slight concern (27%) about the initial failure. In a separate sample of 43 new mothers whose infants failed the second-stage screening and were awaiting audiologic follow-up, 18 (42%) reported no concern while 16 (37%) reported only slight concern. The researchers offered some possible explanations for these suprising results. One was that the program was ineffective in educating parents about the effects of hearing loss and the importance of early identification. Alternatively, they suggested that the apparently low level of maternal concern may actually have reflected parents' heightened sensitivity to the possible hearing problem. As a result, the authors theorized, mothers in the study may have observed their infant's behavior more closely and seen evidence that their infant was not hearing-impaired.

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