Contralateral masking for monaural speech intelligibility measurements with hearing aids in free-field speech conditions
AbstractPatients with asymmetrical hearing loss or unilateral hearing loss often suffer from bad hearing at the poor side, from localisation problems, and from poor speech understanding in noise. In many cases speech audiometry in free field can be an effective tool to decide whether speech understanding is equivalent for both aided ears, making binaural interaction possible, but only if the speech intelligibility is measured for each ear separately. However, it is difficult to evaluate the effectiveness of each (aided) ear individually. This is due to the fact that sound generated in free field can reach both ears, i.e., also the non-test ear. The sound can reach the non-test ear in three ways: directly from the loudspeaker, indirectly by transcranial transmission via the test ear (cross-hearing), or via the skull. In many clinics the non-test ear is “masked” by a foam plug and/or earmuffs. This method helps to minimise the effect of hearing direct sound at the non-test ear. However, transcranial transmission cannot be ruled out by this method. We suggest a new method of contralateral masking, while stimulating in free field. Theoretical considerations are outlined to determine the masking levels necessary to mask sufficiently, and to avoid too much masking (over-masking). For most asymmetric hearing losses a simple rule can be used.a
3M Occupational Health Group. (2010). Technical Datasheet E-A-R™ Classic™ Roll-Down Earplugs, www.3m.com.
ANSI S3.6. (2004). American National Standard Specifications for Audiometers.
Berger, E.H. (1984). “Attenuation of earplugs worn in combination with earmuffs,” Occup. Health Saf., 16, 72-73.
Berger EH, Kieper RW, and Gauger D. (2003). “Hearing protection: Surpassing the limits to attenuation imposed by the bone-conduction pathways,” J. Acoust. Soc. Am., 114, 1955-1967.
Clark, J.L. and Rosser, R.J. (1988). “Three studies comparing performance of the ER-3A tubephone with the TDH-50P earphone,” Ear Hearing, 9, 268-274.
ER-3A Product Sheet. Etymotic Research, Inc., www.etymotic.com
Fagelson, M.A., Noe, C., Murnane, O., and Blevins, J. (2003). “Predicted gain and functional gain with transcranial routing of signal completely-in-the-canal hearing aids,” Am. J. Audiol., 12, 137-145.
Gudmundsen, G.I. (1997). “Physical options,” In: Tobin, H. (Ed.). Practical Hearing Aid Selection and Fitting, Washington, D.C.: Department of Veterans Affairs, pp. 1-16.
Munro, K. and Agnew, N. (1999). “A comparison of inter-aural attenuation with the Etymotic ER-3A insert earphone and the Telephonics TDH-39 supra-aural earphone,” Br. J. Audiol., 33, 259-262.
Munro, K.J. and Contractor, A. (2010). “Interaural attenuation with insert earphones,” Int. J. Audiol., 49, 799-801.
Sklare, D.A. and Denenberg, L.J. (1987). “Interaural attenuation for Tube Phone (R) insert earphones,” Ear Hearing, 8, 298-300.
Valente, M., Potts L.G., Valente, M., and Goebel, J. (1995). “Wireless CROS versus transcranial CROS for unilateral hearing loss,” Am. J. Audiol., 4, 52-59.
Voss, S.E., Rosowski. J.J., Merchant, S.N., Thornton, A.R., Shera, C.A., and Peake, W.T. (2000). “Middle ear pathology can affect the ear-canal sound pressure generated by audiologic earphones,” Ear Hearing, 21, 265-274.
Zwislocki J. (1957). “In search of the bone-conduction threshold in a free sound field,” J. Acoust. Soc. Am., 29, 795-804.
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