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C. Elberling Oticon ’Eriksholm’ Denmark

Efficient stimuli for frequency specific ASSR. C. Elberling Oticon ’Eriksholm’ Denmark. EHDI Conference, Atlanta, USA – March 2005. T. Berger Philips-Univ. Marburg Germany. E. Stürzebecher & M. Cebulla Johann Wolfgang Goethe-Univ. Frankfurt Germany. The problem.

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C. Elberling Oticon ’Eriksholm’ Denmark

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  1. Efficient stimuli for frequency specific ASSR C. Elberling Oticon ’Eriksholm’ Denmark EHDI Conference, Atlanta, USA – March 2005 T. Berger Philips-Univ. Marburg Germany E. Stürzebecher & M. Cebulla Johann Wolfgang Goethe-Univ. Frankfurt Germany

  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. Click - ASSR 0 10 40 50 ms 20 30 Freq-spec ASSR lower amplitude Response amplitude - 90 stimuli/second => longer test time

  4. Amplitude Time FC Amplitude FM FM Frequency Amplitude Modulation - AMFR

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

  6. Brainstem The Auditory Pathway

  7. 40 30 Amplitude [dB arb] 20 10 0 500 1000 1500 0 Frequency [Hz] 1000 Hz

  8. 1000 Hz

  9. 1000 Hz

  10. 40 30 Amplitude [dB arb] 20 10 0 0 500 1000 Frequency [Hz] 500 Hz 500 7cos

  11. Cochlea travel time

  12. PC 500 7cos PC 40 30 Amplitude [dB arb] 20 10 0 0 500 1000 Frequency [Hz] 500 Hz

  13. 40 Stimulus 500 7cos PC 30 Amplitude [dB arb] 20 10 0 0 500 1000 Response Frequency [Hz] 500 Hz

  14. FO 40 Stimulus 500 7cos PC FO 30 Amplitude [dB arb] 20 10 0 0 500 1000 Response Frequency [Hz] 500 Hz

  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 Mardia’s q-sample test (six harmonics) • Error probability α = 1%

  16. 0.2 Relative frequency 0.1 median 0 0 50 100 150 200 250 300 Detection time (s) 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

  17. ns ns p < 0.05 p < 0.02 p < 0.02 p < 0.01 RESULTS: 500 Hz

  18. ns p < 0.01 p < 0.02 p < 0.01 RESULTS: 2000 Hz

  19. BW ~ 540 Hz ns p < 0.02 BW ~ 900 Hz app.. 1/3-oct. RESULTS: 1000 & 4000 Hz

  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

  21. END

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