The Selection and Validation of Output Sound Pressure Level in Multichannel Hearing Aids

Objective To validate the Australian National Acoustic Laboratories’ (NAL) procedure for prescribing output sound pressure level (OSPL) for multichannel hearing aids (Dillon & Storey, 1998) Design The NAL OSPL prescriptive procedure for multichannel hearing aids was used to calculate Predicted OSPL, Predicted Maximum Acceptable OSPL and Predicted Minimum Acceptable OSPL for 20 subjects with sensorineural hearing loss fitted with a 2-channel linear hearing aid. Subjects rated the speech clarity and quality of average (65 dBA) and loud (80 dBA) speech, in quiet and in noise, with the hearing aid set to a number of OSPL settings. These data were used to evaluate the validity of the Predicted OSPL. Frequency-specific loudness discomfort levels (LDLs) were measured to determine whether use of measured LDLs would improve the accuracy of the prediction. Results The Predicted Minimum Acceptable OSPL was in good agreement with the measured minimum acceptable OSPL for both the low- and high-frequency channels. The Predicted Maximum Acceptable OSPL was in good agreement with the measured maximum acceptable OSPL for the low-frequency channel, but was only a fair predictor for the high-frequency channel. The use of measured LDLs rather than predicted LDLs did little to improve the accuracy of the fitting. A direct comparison between the NAL single-channel and multichannel prescribed OSPL settings showed that most listeners rated speech clarity higher for the multichannel settings. Conclusions In two channel hearing aids, the NAL Predicted Minimum Acceptable OSPL and Predicted Maximum Acceptable OSPL are reasonable predictors of minimum and maximum OSPL levels measured using sound clarity and quality ratings. The results of this study support the use of the NAL prescriptive formula for setting OSPL in multichannel hearing aids. Such settings should be verified by having the listener rate the loudness of an intense speech signal. If tolerance problems are evident, the OSPL in the high-frequency channel(s) should be reduced first.

[1]  E. Owens,et al.  An Introduction to the Psychology of Hearing , 1997 .

[2]  Harvey Dillon,et al.  Loudness discomfort level measurements and their implications for the design and fitting of hearing aids , 1984 .

[3]  D D Dirks,et al.  Effect of sensorineural hearing loss on loudness discomfort level and most comfortable loudness judgments. , 1978, Journal of speech and hearing research.

[4]  R H Margolis,et al.  Magnitude estimation of loudness. I: Application to hearing aid selection. , 1984, Journal of speech and hearing research.

[5]  R A Bentler,et al.  An Examination of Several Characteristics that Affect the Prediction of OSPL90 in Hearing Aids , 2001, Ear and hearing.

[6]  D D Dirks,et al.  Subjective Judgments of Speech Clarity Measured by Paired Comparisons and Category Rating , 1997, Ear and hearing.

[7]  H Dillon,et al.  The National Acoustic Laboratories' procedure for selecting the saturation sound pressure level of hearing aids: theoretical derivation. , 1998, Ear and hearing.

[8]  D D Dirks,et al.  Subjective judgements of clarity and intelligibility for filtered stimuli with equivalent speech intelligibility index predictions. , 1998, Journal of speech, language, and hearing research : JSLHR.

[9]  H. Dillon,et al.  The National Acoustic Laboratories' (NAL) New Procedure for Selecting the Gain and Frequency Response of a Hearing Aid , 1986, Ear and hearing.

[10]  R. Beattie,et al.  IHAFF loudness contour test: reliability and effects of approach mode in normal-hearing subjects. , 1997, Journal of the American Academy of Audiology.

[11]  C V Pavlovic,et al.  Reliability, sensitivity and validity of magnitude estimation, category scaling and paired-comparison judgements of speech intelligibility by older listeners. , 1992, Audiology : official organ of the International Society of Audiology.

[12]  C. Speaks,et al.  Subjective vs. objective intelligibility of sentences in listeners with hearing loss. , 1998, Journal of speech, language, and hearing research : JSLHR.

[13]  S. C. Purdy,et al.  FIABILITE, SENSIBILITE ET VALIDITE DU JUGEMENT DE L'INTELLIGIBILITE DE LA PAROLE OBTENUES PAR ESTIMATION DE LA GRANDEUR, ESTIMATION CATEGORIELLE ET COMPARAISON PAR PAIRES CHEZ DES SUJETS AGES , 1992 .

[14]  R M Cox,et al.  Evaluation of the speech intelligibility rating (SIR) test for hearing aid comparisons. , 1992, Journal of speech and hearing research.

[15]  R M Cox,et al.  The Contour Test of Loudness Perception , 1997, Ear and hearing.

[16]  C. Palmer,et al.  Reliability of the Contour Test in a population of adults with hearing loss. , 1998, Journal of the American Academy of Audiology.

[17]  H Dillon,et al.  The National Acoustic Laboratories' Procedure for Selecting the Saturation Sound Pressure Level of Hearing Aids: Experimental Validation , 1998, Ear and hearing.

[18]  R M Cox,et al.  Development of the Speech Intelligibility Rating (SIR) test for hearing aid comparisons. , 1989, Journal of speech and hearing research.

[19]  R C Beattie,et al.  Loudness Discomfort Level for Speech: Comparison of Two Instructional Sets for Saturation Sound Pressure Level Selection , 1980, Ear and hearing.