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 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

ms Click - ASSR Freq-spec ASSR lower amplitude Response amplitude - 90 stimuli/second => longer test time

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

5 90 Hz 180 Hz 270 Hz 360 Hz 450 Hz 540 Hz 630 Hz 720 Hz Frequency [Hz] Amplitude [dB] Amplitude spectrum of the ASSR Response components + Noise Noise

6 Brainstem The Auditory Pathway

7 Amplitude [dB arb] Frequency [Hz] Hz

8

9

10 Frequency [Hz] Amplitude [dB arb] Hz 500 7cos

11 Cochlea travel time

12 Frequency [Hz] Amplitude [dB arb] Hz 500 7cos PC PC

13 Frequency [Hz] Amplitude [dB arb] Stimulus 500 7cos PC Response 500 Hz

14 Frequency [Hz] Amplitude [dB arb] Hz Response Stimulus 500 7cos PC FO FO

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 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 Detection time (s) Relative frequency median

c PCOne-sample cOne-sample c PC FOq-sample Stimulus Statistics Detection Rate [%] Detection Time [s] Performance Index, PI 500 AMOne-sample RESULTS: 500 Hz ns p < 0.05p < 0.02 p < 0.01

18 Stimulus Statistics Detection Rate [%] Detection Time [s] Performance Index, PI 2000 AMq-sample cq-sample c PCOne-sample c PCq-sample RESULTS: 2000 Hz ns p < 0.01 p < 0.02 p < 0.01

19 Stimulus Statistics Detection Rate [%] Detection Time [s] Performance Index, PI cq-sample c PCOne-sample c PCq-sample cq-sample c PCq-sample c PCq-sample BW ~ 540 Hz BW ~ 900 Hz app.. 1/3-oct. RESULTS: 1000 & 4000 Hz ns p < 0.02

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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