1. Interference in Hearing Aids from Digital Wireless Telephones: Improved Predictive Methods H. Levitt, M. Bakke, Kozma- Spytek, L., Verhoff, J. Gallaudet University

2. Subjects Number: 40 minimum in a balanced design Criteria for inclusion: –Hearing aid wearer, –uses cell phone, –age will not be a criterion for inclusion Recruitment: –local hearing centers, –by newspaper advertisements, –HLAA e-newsletter –internet sites Reimbursement: $12/hour or fraction thereof for participation.

3. Stimuli Stimuli: 5 forms of interference will be considered, 4 transmission technologies and 1 reference form of interference (HINT speech noise). –GSM (AMR, NB, Full Rate, 12.2 kb) –*iDEN –*CDMA (Full Rate) –UMTS(wideband CDMA, AMR, Full Rate, 12.2 kb) * Waiting to hear from Kevin Butler from Sprint/Nextel regarding specific codec characteristics to use for iDEN and CDMA simulations

4. Tests Tests: Three computer tests will be administered –Threshold, –Boundary & –Speech Recognition

5. Threshold Test Simple adaptive procedure to determine the threshold S/N at which the subject is aware of noise. The S/N will be adjusted accordingly until the specified number of reversal pairs has been obtained.

6. Boundary Test Adaptive procedure similar to the Threshold Test Purpose: to determine the boundary SIR for different subjective ratings of sound quality Trials for the 3 boundaries will be interleaved Testing will continue until the specified numbers of reversals have been obtained for all 3 tests. Using the categories from C63.19 –B1- Excellent Performance / Acceptable for normal use –B2 – Acceptable for normal use / Usable for a brief call –B3 – Usable for a brief call / Not usable

7. Categories EXCELLENT PERFORMANCE: You would find a phone with this level of noise to be highly usable. You would have no complaints about this amount of noise for extended phone calls. ACCEPTABLE FOR NORMAL USE: You would find this level of noise to be acceptable for normal, regular use of a phone. You would accept this amount of noise for an extended phone call without becoming tense or tired. USABLE FOR A BRIEF CALL: With this level of noise you could successfully complete a brief phone call. However, you would not accept this amount of noise for normal, regular phone use. NOT USABLE: With this level of noise, you would not be able to complete even a brief phone call. You could not accept this amount of noise for any type of phone use.

8. Speech Recognition Test Percent correct score for HINT test material at 2 fixed speech-to-interference ratios (SIRs) SIRs correspond to best two boundaries (B1 and B2) Direct-audio-input connection to Phonak behind-the-ear hearing aid fit to the subject’s hearing loss Speech is prerecorded and passed through a codec or telephone band. –Codecs depend on type of technology (GSM, iDEN, CDMA & wideband CDMA).

9. So far... InterfererCodec A = GSMAMR codec, NB, Full Rate, 12.2 kb B = iDENABME ++ codec proprietary to Motorola C = CDMAEVRC codec D = UMTSWideband CDMA – EVRC codec, R = ReferenceTelephone band

10. Major issue at present Choosing the best selection of parameters for technologies and codecs Requests for information from industry have yielded some information Information so far is incomplete

11. Summary 40 subjects with hearing loss 4 technologies & reference noise Tests –Thresholds –Boundaries between categories –Speech recognition for sentences Problem: determining “best” parameters for technologies and codecs