Contributions of Peripheral Spatial Resolution to Speech Perception in Cochlear Implant Users

Statistical ConsultingFebruary 11, 2013

8:30 – 9:20 am30 Schaeffer Hall

Background

• Personal– Clinical Audiologist– PhD Student in Hearing Science working on

Dissertation• Research Project

– Cochlear Implant Users

Two Prevailing Questions in Cochlear Implant Research

• Why is there so much variability in performance among individuals who use cochlear implants?

• When children are implanted, how can we form realistic expectations about their potential performance? How can the clinician ensure that the device is programmed optimally?

Cochlear Implant

Auditory Nerve

Cortex Perception

ECAP ACC Speech

Hearing Loss

Simple Complex

• ECAP Channel Interaction Functions– Thirteen channel interaction functions total– Quantified as an area of separation (channel

separation index) between two functions

Masker Electrode

5 10 15 20

Am

ount

of M

aski

ng

0.0

0.2

0.4

0.6

0.8

1.0

Goal 1. Auditory Nerve and Cortex

Masker Electrode

5 10 15 20

Am

oun

t of

Mas

king

0.0

0.2

0.4

0.6

0.8

1.0

pair e11-e5

Electrode

5 10 15 20

norm

am

p

0.0

0.2

0.4

0.6

0.8

1.0

pair e11-e9

Electrode

5 10 15 20

norm

am

p

0.0

0.2

0.4

0.6

0.8

1.0

pair e11-e17

Electrode

5 10 15 20no

rm a

mp

0.0

0.2

0.4

0.6

0.8

1.0

separation e11 componentseparation other electrodeinteraction

pair e11-e6

Electrode

5 10 15 20

pair e11-e7

Electrode

5 10 15 20

pair e11-e8

Electrode

5 10 15 20

pair e11-e14

Electrode

5 10 15 20

norm

am

p

0.0

0.2

0.4

0.6

0.8

1.0

pair e11-e10

Electrode

5 10 15 20

pair e11-e12

Electrode

5 10 15 20

pair e11-e13

Electrode

5 10 15 20

pair e11-e16

Electrode

5 10 15 20

norm

am

p

0.0

0.2

0.4

0.6

0.8

1.0pair e11-e15

Electrode

5 10 15 20

Goal 1. Auditory Nerve and Cortex

• Simple ACC– Thirteen electrode pairs to assess discrimination

Time (ms)

0 200 400 600 800 1000 1200

Am

plit

ude

(m

icro

V)

-15

-10

-5

0

5

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16

Nor

m A

CC

Am

plitu

de

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

B

B

B

B BB

B

A

A AA

A

AA

Channel Separation Index

0.0 0.1 0.2 0.3 0.4 0.5

Nor

m A

CC

Am

plitu

de

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

B

BB

B

B

B

BA

A

A AA

AA

F19R

E60

Can ECAP channel separation indices predict simple ACC amplitude?Sub-question: Are there 2 unique curves or just 1?

Channel Separation Index

0.0 0.1 0.2 0.3 0.4 0.5

No

rm A

CC

Am

plit

ude

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

B

BB

B

B

B

BA

A

A AA

AA

B

B

B

BBB

B

A

AAA

A

AA

F19RE60

Assume a monotonically increasing, saturating function:

y=a(1-e-x/b)

Goal 2. Simple versus Complex Stimulation

• Complex ACC– Three experimental speech processor programs,

each uses a different subset of 7 electrodes from the 13 used for ECAP and simple ACC measures

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

P1 X X X X X X X

P2 X X X X X X X

P3 X X X X X X X

Goal 2. Simple versus Complex Stimulation

• Three sets cortical responses to complex stimuli.

Time (ms)

0 200 400 600 800 1000 1200

Am

plit

ude

(m

icro

V)

-15

-10

-5

0

5

Can ECAP channel separation indices and/or cortical responses to electrode changes predict a cortical response to a complex change?

Average ECAP Channel Separation Index

0.00 0.05 0.10 0.15 0.20 0.25 0.30

Co

mp

lex

AC

CR

ipp

le D

ep

th T

hre

sho

ld

0

10

20

30

40

50

60

E60Plot 1 RegrF19RPlot 2 Regr

Calculated Simple ACC

0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.500

10

20

30

40

50

60

Goal 3. Speech Perception

• Three vowel perception scores (% correct), one for each experimental program.

• Three “signal-to-noise ratios” for 50% correct, one for each experimental program.

Can ECAP channel separation indices, cortical responses to electrode changes and/or cortical responses to complex changes predict speech perception?

Average Channel Separation Index

0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18Vo

we

l Pe

rce

ptio

n (%

Co

rre

ct)

20

30

40

50

60

70

E60F19R

Calculated Spatial ACC

0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.5020

30

40

50

60

70

Ripple Depth Threshold

0 10 20 30 40 50 6020

30

40

50

60

70

*Repeat analysis using a speech-in-noise test as the speech perception measure.*

Average ECAP Channel Separation Index

0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18Vo

we

l Pe

rce

ptio

n (%

Co

rre

ct)

20

30

40

50

60

70

E60F19R

Calculated Simple ACC

0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.5020

30

40

50

60

70

Complex ACCRipple Depth Threshold

0 10 20 30 40 50 6020

30

40

50

60

70

Progress to Date and Plans

• Data Collection:– 2 pilot subjects have completed testing– Plan: 10 subjects total

• Decisions I still have to make: – ECAP: use raw or normalized amplitudes– ECAP: use an average or maximum separation index– Simple ACC: use raw or normalized peak-to-peak

amplitudes or raw or normalized rms amplitudes– Complex ACC: ripple depth threshold or rms amplitude

at a set ripple depth

Project SummaryGoal 1: Auditory Nerve versus Cortex for Simple Stimulation

– 13 ECAP Channel Separation Indices (6 Basal, 6 Apical, 1 Zero Point)– 13 Spatial ACC (6 Basal, 6 Apical, 1 Zero Point)

Goal 2: Simple versus Complex Stimulation– 3 ECAP Channel Separation Indices (average of the adjacent electrodes in the

experimental program)– 3 Calculated Simple ACC Amplitudes—from the coefficients determined in Goal 1– 3 Ripple Depth Thresholds from Complex ACC Amplitudes

Goal 3: Speech Perception– 3 ECAP Channel Separation Indices– 3 Calculated Simple ACC Amplitudes—from the coefficients determined in Goal 1– 3 Ripple Depth Thresholds from Complex ACC Amplitudes– 3 Vowel Perception Scores – 3 Speech-in-noise Scores