The effectiveness of the Navy's Hearing Conservation Program.

The purposes of this study were to determine the incidence of significant threshold shift (STS) for a large number of Naval fleet personnel, evaluate hearing conservation program (HCP) compliance for a large number of Naval ships, and determine whether two currently used compliance measures are useful means of evaluating HCP effectiveness. Data were collected from 12,492 medical records of 154 ships/submarines regarding STS incidence and follow-up, percent of valid audiograms, and other HCP elements. Data analyses suggested that STS incidence (29%) and follow-up compliance (62%) among fleet personnel may be too high and low, respectively, although audiogram compliance is 80.0 to 92.9%. Also, checklists commonly used to evaluate HCP compliance were not highly correlated with STS incidence. The data support literature recommendations for audiometric data base analyses to evaluate HCP effectiveness and for training for medical officers involved in the HCP. Recommendations and future implications are discussed.

Demonstration of binaural advantage in audiometric test rooms.

Binaural advantage was measured for 12 normally hearing subjects in a typical rectangular audiometric test room with a loudspeaker located in each corner. Four different loudspeaker configurations for presentation of signal and competition were evaluated. The results indicated that a configuration in which uncorrelated competition was delivered from both sides of the subject while the signal was presented from a 0 degree azimuth was the most resistant to interaural asymmetries resulting from the room geometry and produced the most consistent binaural advantages. Binaural advantage was then measured using this loudspeaker configuration for 15 hearing-impaired individuals wearing hearing aids. Although the group results indicate a mean unaided binaural advantage only slightly smaller than seen in the normal hearers, when hearing aids were worn an interaural asymmetry in a signal-to-competition ratio developed that reduced the clinical usefulness of the data for individuals. This outcome emphasizes that a valid clinical demonstration of binaural advantage is critically dependent on interaural symmetry in signal-to-competition ratios for both aided and unaided tests. Such symmetry may be difficult to achieve in a typical audiometric test room.

Earmold modification effect measured by coupler, threshold and probe techniques.

The validity of probe tube microphone measurements in providing data indicative of the magnitude of the change in subjects' threshold resulting from changes in earmold configuration was investigated. The relationship between these measures in the real ear canal and the changes observed in 2-cm3 and Zwislocki couplers under similar circumstances or earmold modification was also measured. Standard, vented and 'open' earmold conditions were utilized. Threshold and probe-tube measurements were made. Statistical evaluation revealed that these two techniques did not produce significantly different results except at 125--165 Hz, where noise masking may have been a factor influencing the threshold data. Neither coupler as used gave an accurate quantitative estimate of the in-use effects of vented earmolds or the open earmold configuration, but the Zwislocki coupler gave a better approximation than the 2-cm3 coupler.