Language Engineering Applications Hearing and ... - KU Leuven

Language Engineering Applications 

Hearing and cochlear implants 

Laboratory for 

Experimental ORL 

K.U. Leuven

The auditory system 

Lab Exp ORL 

KULeuven 

The outer ear - the visible part that collects and directs sound 

to the middle ear 

The middle ear- includes the eardrum and three tiny bones 

that send sound to the inner ear. 

The inner ear - contains the cochlea, that includes the sensory 

cells for hearing. These sensory cells are called hair cells.

Normal hearing in a nutshell 

Lab Exp ORL 

• Sound is picked up from the environment by the outer ear and transmitted as 

sound waves down the ear canal to the eardrum. 

• The sound waves cause the eardrum to vibrate which sets the three tiny bones 

(malleus, incus and stapes) in the middle ear into motion. 

• The motion of these tiny bones makes the fluid in the inner ear, or cochlea, 

vibrate. 

• The vibration of the inner ear fluid causes the hair cells in the cochlea to move 

(organ of Corti). The hair cells change this movement into electrical impulses. 

• The electrical impulses are carried by the hearing (auditory) nerve fibers up to 

the brain where they are interpreted as sound. 

KULeuven

The organ of Corti - crucial for hearing! 

Lab Exp ORL 


3500 inner hair cells 

25000 outer hair cells

Coding of frequency by place in the cochlea 

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• Base: basilar membrane is stiffest 

• Apex (the top): basilar membrane is wider and less stiff 


Hearing loss 

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• Audiograms of otitis media 

(inflammations of the middle 

ear). Results in conductive 

hearing loss (hair cells are 

not damaged). 


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Hearing loss continued 

• Noise-induced hearing loss (damaging effect due to stimulation as high sound 

levels: sensorineural) 


Lab Exp ORL 

Hearing loss continued 

• Presbycusis: age-related auditory impairments 


Lab Exp ORL 

Hearing loss (Cochlear) 

• Any of the three sections of the ear, outer, middle or inner may not work 

correctly and cause a hearing loss. 

• Sensorineural Hearing Loss 

• If the inner ear is not functioning correctly, this can cause a sensorineural 

hearing loss or nerve deafness. When there is sensorineural hearing loss the 

hair cells that line the cochlea have been damaged. The damaged hair cells 

cannot send the electrical impulses (release of a neurotransmitter) to the 

hearing nerve so the brain does not receive complete sound information. The 

greater the hair cell damage, the greater the hearing loss. 

• Inner and outer parts of hair cells contain chemical substances with a different 

ionic composition. Displacement of the basilar membrane cause release of 

neurotransmitter: generation of action potentials. 


• Sensorineural loss can be caused by many factors including genetics (born 

deaf), injury, illness, or can be part of the natural ageing process. Sometimes 

drugs, which are used to treat life-threatening illnesses, can also damage the 

inner ear.

Cochlear implant 

Lab Exp ORL 

• A cochlear implant device bypasses the outer, middle, and part of the 

ear, including the hair cells, and stimulates the auditory nerve directly 

through an array of electrodes placed as well as possible in the 

bone. 


• Hearing aid versus cochlear implant 

– While a conventional hearing aid amplifies the acoustic signal 

outer, middle and inner ear, a cochlear implant stimulates the 

nerve electrically. 

– Designed to provide hearing and improved communication ability to 

individuals who are profoundly hearing impaired and who derive 

or no benefit from conventional hearing aids. 

– Amplification does not help the profoundly deaf 

– For implantees with good nerve survival, multiple electrodes can 

‘place’ representation of frequencies in the normal cochlea: 

towards the base of the cochlea stimulate high-frequency sounds, 

towards the apex stimulate lower frequencies.

Inclusion criteria 

Lab Exp ORL 

• Patients with profound bilateral sensorineural hearing loss (FI 90dB) in both 

ears as determined by standard audiometrical testing 

• Pre- and postlingually deafened 

• Patients scoring less than 40% on open-set sentence recognition in the bestaided 

listening condition with conventional hearing aids. 

• Patients can also be considered candidates after extensive consideration by a 

knowledgeable NKO surgeon. 

• Patients must have past ORL, audiological, anaesthesiological and radiological 

tests as well as psychological evaluations. 

• Patients must be capable of performing tests, although mentally impaired 

people can also benefit from an implant 

• Multidisciplinary team at work! 


Exclusion criteria 

Lab Exp ORL 


• Patients who have a marked benefit from conventional hearing aid as 

determined by standard audiometrical tests 

• Patients with a lack of recognizable acoustic nerve on MRI examination and/or 

negative results on the pre-operative electro-stimulation test. 

• Patients with a medical contra-indications to electrode insetion or receiver 

placement e.g. malformation and/or ossification of the cochlea 

• Patients with chronic ear disease such as tinnitus 

• Patients with deafness due to lesions of the acoustic nerve or central auditory 

pathway 

• Patients with negative results of the pre-operative electro-stimulation test 

• Patients with a duration of deafness exceeding 15 yrs 

• .Patients with allergy to the insertion gel Triamcinolone acetonide (= Kenacort 

A®) 

• Motivation! 

• ....

Lab Exp ORL 

Cochlear implant 

• Sound is received by the microphone 

• The sound is analyzed and digitized into coded signals by an internal chip. 

• Coded signals are sent to the transmitter. 

• Transmitter sends the code across the skin to the internal implant where it is 

converted to electronic signals. 

• Signals are sent to the electrode array to stimulate the hearing nerve fibres in 

the cochlea. 

• Signals travel to the brain where they are recognized as sounds producing a 

hearing sensation. 


The Laura cochlear implant 

Lab Exp ORL 

Coil on the 

skin 

Coil under 

the skin 

BTE + 

microphone 

Decoding + 

Current 

Sources 

Speech 

Processor 

(DSP) 

Electrode array 

inserted in cochlea 

External 

Internal 


ps. L. Geurts

Insertion of electrode array 

Lab Exp ORL 


Specifications of LAURA implant device 

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• Array of 16 electrodes of which each adjacent pair of electrodes is defined as a 

bipolar channel. 

• The overall stimulation rate for the standard biphasic current pulses of 40 ms 

per phase is fixed at 10,000 pulses per second. 

• The rate per channel depends on the number of active channels. For a standard 

setting, a biphasic current pulse is sent to one of the active channels each 100 

ms. Hence, the stimulation rate for eight active channels is 1250 pulses per 

second per channel. 

• Besides the standard pulse width of 40 ms/phase, biphasic pulses of 100 

ms/phase and 200 ms/phase can also be used, but then only at lower 

stimulation rates. 


• In the Laura Flex the acoustical input received by the microphone is filtered by 

as many as eight fourth-order bandpass filters from 100 Hz to 5000 Hz, one for 

each active channel. The most important frequencies for speech intelligibility 

range between 100 and 5000 Hz.

Lab Exp ORL 

Specifications of LAURA implant device 

• The filters have a linear spacing from 100 Hz to a transition frequency of 

approximately 800 Hz, and with a logarithmic spacing from the transition 

frequency to 5000 Hz. If less than 8 channels are activated, the filter bands are 

re-arranged over the 100-5000 Hz interval. The frequency bands are grouped 

together, from high to low. The latter implies that high frequency cues become 

more difficult to differentiate than low frequency ones when less electrodes are 

active. 

• After envelope detection and compression, which is done in a manner 

comparable to the CIS algorithm (Wilson et al. 1991), the electrical variations 

are transmitted to the internal device through a transcutaneous link. Amplitude 

is coded by changing the amplitude of the electrical pulse, not the duration. 


Signal is filtered, temporal envelope is determined, compression, 

modulated, CIS... 

Lab Exp ORL 

verzwakking (dB) 

10 

0 

-10 

-20 

-30 

-40 

-50 

/ie/ 

100 1000 

frequentie (Hz) 


Plot L. Geurts

Top: Output of the CIS algorithm for the word ‘som’. Pulse channels reflect the envelopes 

of the bandpass filter output. Below: more detailed overview. 

8 

Lab Exp ORL 

7 

A 

amplitude per channel 

6 

5 

4 

3 

2 

1 

100 200 300 400 500 600 700 800 900 

time (ms) 

8 

B 

amplitude per channel 

7 

6 

5 

4 

3 

2 


1 

384 386 388 390 392 394 396 

time (ms) 

ps L. Geurts

Lab Exp ORL 


Transmission of /ama/ and /asa/ by the Laura implant 

Lab Exp ORL 


Lab Exp ORL 

One month after surgery 

• Fitting of the implant 

– determine thresholds and most comfortable levels for each channel 

(= pair of electrodes). 

– Determined with tones and speech. 

– Signal is mapped onto dynamic range (mcl-level) 

– Start of rehabilitation programme 


Speech perception assessment 

Lab Exp ORL 


• Speech perception assessment is required for 

• diagnostic purposes 

• monitoring progress in a rehabilitation program 

Lab Exp ORL 

• comparing different speech processing strategies 

• other research purposes 

• Basic test requirements: 

• Sensitivity refers to the extent to which a test is capable of measuring specific aspects 

in performance. A sensitive test should demonstrate, for example, differences in 

performance for persons with different degrees of hearing loss, or differences in 

performance for (normal hearing) persons with different psychophysical capabilities. 

• Validity: A test is valid if it measures what it is supposed to measure. Validity is a 

prerequisite for sensitivity. One should always be aware of the issue under interest, and 

be reserved with using tests with populations for which they were not intended. Also, 

one should be careful with correlating the obtained results with other (existing speech 

perception) measures. This may not be appropriate. 

• Reliability concerns the extent to which measurements are repeatable. Each type of 

measurement involves some degree of random error. Effect of random errors can be 

reduced by repeating the stimuli several times in the same test. 


Analytical tests 

Lab Exp ORL 

• quantify transmission of speech cues (duration, F1, F2, voicing, burst, 

frication) 

• important that listener responds to auditory information only - no meaningful 

context 


Lab Exp ORL 

Formant frequencies of Dutch vowels 

spoken in Belgium (F1 & F2) 

3000 

i 

Second formant frequency (Hz) 

2500 

2000 

1500 

1000 

500 

y 

i 

i 

I 

y 

u 

u 

u 

u 

i 

e 

I 

e 

y 

 

o 

o 

e 

 

o 

I 

 

 

) 

 

 

 

- 

) 

 

- 

- 

) 

a 

a 

a 

- 

a 

W D - fem ale 

MD - male 

JW - male 

0 

A G - fem ale 

200 

400 

600 

800 

1000 

1200 


First form ant frequency (Hz)

Lab Exp ORL 

Speech properties of consonants 

• voicing, /p/ vs. /b/ - low frequency 

• manner of articulation, nasals vs. fricatives (temporal 

cues) 

• place of articulation, /p/ vs. /t/ vs. /k/ (spectral cues) 


Lab Exp ORL 

Nonsense speech material 

• 10 vowels in context of pVt or hVt V= /u, y, i, o, e, a, ), I, 

,,-, / 

• 16 consonants in context of /a/,/u/, /i/ /p, t, k, b, d, r, l, m, n, s, f, 

:, z, v, g, j / 

• 2 male and 2 female speakers 

• same RMS level for all stimuli 


Lab Exp ORL 

APEX 

(Application for Psycho-Electrical Experiments) 

for this test: acoustical, closed-set 

random order, 12 repetitions of each stimulus 

to loudspeaker - acoustical presentation 

to coil of CI - electrical stimulation, directly to electrodes 

to audio input of CI - electrical stimulation with speech processor 

aPa 

aTa 

aSa 

aMa 

aBa 

aNa 

a 

aKa 

aCHa 


Manner of scoring 

Lab Exp ORL 

• percentage correct: the diagonal 

Stimulus-response confusion matrix 

12 repetitions of each stimulus 

• relative feature transmission scores 

(Miller & Nicely, 1955), duration, F1, 

F2, voicing, frication, etc.. 

paat peet poot pat pet pot 

paat 4 4 2 2 0 0 

peet 1 11 0 0 0 0 

poot 0 3 9 0 0 0 

pat 1 0 0 11 0 0 

pet 0 0 0 0 12 0 

pot 0 0 0 0 3 9 


Lab Exp ORL 

To what extent are spectral and temporal cues 

transmitted with fidelity by Laura device? 

• 25 subjects fitted with Laura Flex speech processor + 

CIS strategy 

• duration of deafness from 1 to > 30 yrs 

• variable number of channels 

• implanted at St. Augustinus in Antwerp, KULeuven & 

Univ. of Nijmegen 


Lab Exp ORL 

Results: vowel identification 

Percentage correct 

100 

90 

80 

70 

Percentage correct (%) 

60 

50 

40 

30 

% correct 

chance 

signif. 

20 

10 

0 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 

Laura implantees (1-25) 


Lab Exp ORL 

Results: consonant identification 

Percentage correct 

100 

90 

80 

Percentage correct (%) 

70 

60 

50 

40 

30 

% correct 

chance 

signif. 

20 

10 

0 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 

Laura implantees (1-25) 


Perceptual dimensions vowels 

Lab Exp ORL 

.6 

 

i 

I 

D2: Duration 

0.0 

y 

u 

) 

a 

e 

o 

 

-.6 

-.6 

0.0 

.6 


D1: Peak level energy

Perceptual dimensions consonants 

Lab Exp ORL 

.6 

r 

D2: Amplitude-envelope 

0.0 

: 

f 

g 

z 

v 

s 

b 

j 

d 

l 

mn 

k 

p t 

-.6 

-.4 

0.0 

.4 


D1: Turbulence

Important perceptual cues 

Lab Exp ORL 

Vowels 

Energy 

Duration 

F1 

Consonants 

Turbulence 

Amplitude envelope 

Other tim e-intensity cues 

F2 


Lab Exp ORL 

Use of analytical information 

in a clinical setting 

• appropriate settings of the CI device? 

• monitor progress in a rehabilitation program 

• time restrictions! 


Study 

Lab Exp ORL 

• select subset of stimuli: 6 vowels, 6 consonants 

• 5 Laura implantees 

• follow-up once a month during a year 

• determine test-retest variability 


Follow-up of one subject 

Lab Exp ORL 

% correct & information transmission (%) 

100 

90 

80 

70 

60 

50 

40 

30 

20 

10 

cons. S4 - preling. 

0 

% corr 

voice 

burst 

place 

fric. 

manner 


% correct & information transmission (%) 

100 

90 

80 

70 

60 

50 

40 

30 

20 

10 

0 

% correct 

duration 

5 ch's, f, 42 yrs 

F1 

F2 

Dates 

09/05 

30/05 

20/06 

01/08 

05/09 

06/03a 

06/03b 

27/03a 

27/03b

Conclusions 

Lab Exp ORL 

• sensitivity, reliability, validity 

• spectral and temporal cues are transmitted with fidelity by Laura 

• vowels:energy, duration, F1 &F2 

• consonants: amplitude envelope, frication... 

• small tests yield sufficient analytical information about subject’s 

progress and its auditory limitations

Language Engineering Applications Hearing and ... - KU Leuven

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