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Summary PageThe ProblemTo improve the real-time auditory detection and aural analysis capability of passive broadband sonar systems. The FindingsThe most blatant source of acoustic signal degradation on auditory sonar systems is in the acoustic performance of headsets. Recent detection performance data have shown the need for upgrading sonar headsets to reproduce electrical energy accurately over a wider bandwidth. Headphone measurement data on commercially available headphones have shown that headphones of more appropriate bandwidth and frequency-response accuracy have not been of sealedcircumaural design. Headphones designed to completely seal around the listener's ear exhibit low-finequency variations with placement on the head and with deterioration of ear-cushion as a result of a less than perfect seal. Unfortunately, current noise levels preclude use of the more accurate, less variable, open-air types. Reduction of noise levels in sonar spaces to permit use of better headphone designs is a highly desu^ble solution. Recent developments in active noise canceling headsets show promise as an interim solution. A commercial model having adequately flat frequency response has been found and improved through active equalization. A prototype version of this improved headset has been evaluated. ApplicationAdvanced auditory sonar system design. Aural analysis and tactical sonar headphone requirements.Administrative Information This research was carried out under Naval Medical Research and Development Command Work Unit 65856N-M0100.(X)1-5001. It was approved for publication on 27 Jun 95, and designated as NSMRL Report 1197. u Abstract Real-time auditory detection and aural analysis capability of passive broadband sonar systems needs improvement. A weak link in these systems is the use of communicationsbandwidth low-fidelity headsets. Unfortunately, no procedure for headphone (earphone element inside headshell) frequency response measurement exists in military headset specifications. An accurate technique for headphone calibration was devised which provides the earphone element with an acoustic load similar to the one provided by a human wearer. Using this technique, headphone measurement data on commercially available headphones was collected and compared to the current sonar headsets. The advantages and disadvantages of open and sealed circumaural headsets and recent developments in noise canceling headsets are discussed, along with the possibility of reducing noise levels in sonar spaces to permit use of higher fidelity headphone designs.

Theoretical speculations concerning the presence or absence of intermanual transfer under differing conditions of sensorimotor adaptation have assumed that the adaptation produced by them are essentially equivalent. The possibility remains that sensorimotor changes generated by these different exposure conditions may be dissimilar. In order to resolve this, it is necessary to obtain relevant information from exposure conditions that provide adequate controls. Auditory rearrangement produced by functional rotation of the interaural axis by pseudophones (a binaural microphone/earphone array worn on the head), represents an exposure condition with suitable controls. Intermanual transfer of adaptation to rearranged ear-hand coordination produced after exposure to a 30° shift of the interaural axis was therefore investigated. FINDINGS Except for one exposure condition, changes in ear-hand coordination that occur to compensate the distortion induced by the pseudophones, fail to transfer intermanually. Such results suggest a differential representation of the sensorimotor function between the hemispheres. APPLICATION These findings are useful in design of auditory passive detection systems employing auditory tracking. They are for use of systems designers and human factors applications where sensorimotor tasks under conditions of perceptual rearrangement are anticipated. This information is of definite value to Naval medical officers in ear, nose, and throat specialities, and to audiologists.

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