C. ElberlingOticon ’Eriksholm’

Denmark

Efficient stimuli forfrequency specific ASSR

E. Stürzebecher & M. CebullaJohann Wolfgang Goethe-Univ. Frankfurt

Germany

T. BergerPhilips-Univ. Marburg

Germany

EHDI Conference, Atlanta, USA – March 2005

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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

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0 10 20 30 40 50 ms

Click - ASSR

Freq-spec ASSR

lower amplitude

Response amplitude - 90 stimuli/second

=> longer test time

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Am

plitu

de

Time

Frequency

Am

plitu

de

FC

FMFM

Amplitude Modulation - AMFR

5

90 Hz

180 Hz

270 Hz

360 Hz

450 Hz

540 Hz630 Hz

720 Hz

Frequency [Hz]0 100 200 300 400 500 600 700 800

Am

plit

ude

[dB

]Amplitude spectrum of the ASSR

Response components+ Noise

Noise

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Brainstem

The Auditory Pathway

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Am

plitu

de [

dB a

rb]

0

10

20

30

40

Frequency [Hz]

0 500 1000 1500

1000 Hz

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0 5 1 0 1 5 2 0 2 5 3 0T i m e [ m s ]

1000 Hz

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0 5 1 0 1 5 2 0 2 5 3 0T i m e [ m s ]

0 5 1 0 1 5 2 0 2 5 3 0T i m e [ m s ]

1000 Hz

10

Frequency [Hz]

0 500 1000

Am

plitu

de [

dB a

rb]

0

10

20

30

40

500 Hz

500 7cos

11

0 2 4 6 8 10 12D e la y [m s]

100

1000

10000

Fre

qu

en

cy [H

z]

Cochlea delaybased on de Boer (1980) & Greenwood (1990)

Cochlea travel time

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Frequency [Hz]

0 500 1000

Am

plitu

de [

dB a

rb]

0

10

20

30

40

500 Hz

500 7cos PCPC

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Frequency [Hz]

0 500 1000

Am

plitu

de [

dB a

rb]

0

10

20

30

40

Stimulus500 7cos PC

Response

500 Hz

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Frequency [Hz]

0 500 1000

Am

plitu

de [

dB a

rb]

0

10

20

30

40

500 Hz

Response

Stimulus500 7cos PC FO

FO

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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%

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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

0 50 100 150 200 250 300

Detection time (s)

Re

lativ

e f

req

ue

ncy median

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500 7c PC One-sample 85.5 61 1.40

500 7c One-sample 77.4 76 1.02

500 7c PC FO q-sample 91.1 59 1.54

Stimulus Statistics Detection Rate [%]

Detection Time [s]

Performance Index, PI

500 AM One-sample 74.2 109 0.68

RESULTS: 500 Hz

ns ns

p < 0.05 p < 0.02

p < 0.02 p < 0.01

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Stimulus Statistics Detection Rate [%]

Detection Time [s]

Performance Index, PI

2000 AM q-sample 82.0 103 0.80

2000 7c q-sample 91.8 51 1.80

2000 7c PC One-sample 90.2 51 1.77

2000 7c PC q-sample 95.1 49 1.94

RESULTS: 2000 Hz

ns p < 0.01

p < 0.02 p < 0.01

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Stimulus Statistics Detection Rate [%]

Detection Time [s]

Performance Index, PI

1000 7c q-sample 95.2 30 3.17

1000 7c PC One-sample 88.9 37 2.40

1000 7c PC q-sample 96.8 29 3.34

4000 7c q-sample 93.4 79 1.18

4000 7c PC q-sample 95.1 67 1.42

4000 11c PC q-sample 96.7 46 2.10

BW ~ 540 Hz

BW ~ 900 Hzapp.. 1/3-oct.

RESULTS: 1000 & 4000 Hz

ns p < 0.02

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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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