1. C. Elberling Oticon Eriksholm Denmark Efficient stimuli for frequency specific ASSR E. Stürzebecher & M. Cebulla Johann Wolfgang Goethe-Univ. Frankfurt Germany T. Berger Philips-Univ. Marburg Germany EHDI Conference, Atlanta, USA – March 2005

2. 2 The problem Auditory Steady State Response – ASSR Diagnostic evaluation of sensitivity => threshold Frequency specific information Amplitude problem => longer test time ­Broad band clicks ­Frequency specific stimuli How can we reduce test time? ­More efficient detection methods (statistics) ­More efficient stimuli

3. 3 010 2030 4050 ms Click - ASSR Freq-spec ASSR lower amplitude Response amplitude - 90 stimuli/second => longer test time

4. 4 Amplitude Time Frequency Amplitude FCFC FMFM FMFM Amplitude Modulation - AMFR

5. 5 90 Hz 180 Hz 270 Hz 360 Hz 450 Hz 540 Hz 630 Hz 720 Hz Frequency [Hz] 0 100 200 300 400 500 600 700 800 Amplitude [dB] Amplitude spectrum of the ASSR Response components + Noise Noise

6. 6 Brainstem The Auditory Pathway

7. 7 Amplitude [dB arb] 0 10 20 30 40 Frequency [Hz] 0 5001000 1500 1000 Hz

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10. 10 Frequency [Hz] 05001000 Amplitude [dB arb] 0 10 20 30 40 500 Hz 500 7cos

11. 11 Cochlea travel time

12. 12 Frequency [Hz] 05001000 Amplitude [dB arb] 0 10 20 30 40 500 Hz 500 7cos PC PC

13. 13 Frequency [Hz] 05001000 Amplitude [dB arb] 0 10 20 30 40 Stimulus 500 7cos PC Response 500 Hz

14. 14 Frequency [Hz] 05001000 Amplitude [dB arb] 0 10 20 30 40 500 Hz Response Stimulus 500 7cos PC FO FO

15. 15 Experimental design 60 normally hearing young adults (age: 17 – 34 y) Stimuli delivered at 30 dBnHL at a rate of 90/s Each ASSR recorded for 300 s Detection made by statistical methods: ­Modified Raleigh one-sample test (first harmonic) ­Modified Mardias q-sample test (six harmonics) ­Error probability α = 1%

16. 16 Definition of terms Detection Rate [%]: % of responses detected < 300 s Detection Time [s]: time to detect a response (< 300 s) Performance Index, PI: Detection Rate/Detection Time 0 0.1 0.2 050100150200250300 Detection time (s) Relative frequency median

17. 17 500 7c PCOne-sample85.5611.40 500 7cOne-sample77.4761.02 500 7c PC FOq-sample91.1591.54 Stimulus Statistics Detection Rate [%] Detection Time [s] Performance Index, PI 500 AMOne-sample74.21090.68 RESULTS: 500 Hz ns p < 0.05p < 0.02 p < 0.01

18. 18 Stimulus Statistics Detection Rate [%] Detection Time [s] Performance Index, PI 2000 AMq-sample82.01030.80 2000 7cq-sample91.8511.80 2000 7c PCOne-sample90.2511.77 2000 7c PCq-sample95.1491.94 RESULTS: 2000 Hz ns p < 0.01 p < 0.02 p < 0.01

19. 19 Stimulus Statistics Detection Rate [%] Detection Time [s] Performance Index, PI 1000 7cq-sample95.2303.17 1000 7c PCOne-sample88.9372.40 1000 7c PCq-sample96.8293.34 4000 7cq-sample93.4791.18 4000 7c PCq-sample95.1671.42 4000 11c PCq-sample96.7462.10 BW ~ 540 Hz BW ~ 900 Hz app.. 1/3-oct. RESULTS: 1000 & 4000 Hz ns p < 0.02

20. 20 Summary & Conclusion ASSR stimuli designed in the frequency domain ­Cochlea excitation area well defined Correction for Cochlea traveling time, PC ­Same philosophy as behind the Chirp stimulus and the Stacked ABR Frequency off-set, FO ­Provide possibility to use response information at higher harmonics For all Stimuli: ­The new stimuli are significantly more efficient than traditional AM stimuli For low frequency stimuli (500 Hz): ­Phase-Correction increases efficiency significantly ­Frequency Off-set increases efficiency significantly by recruiting more information For high frequency stimuli ­Phase-Correction increases efficiency only marginally

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