Proefschrift_vd

Raw wave forms are shown in Figure 1, D. The recording electrode contact was set two contacts apical to

the fixed masker contact (as Abbas et al, 1999) and in five patients the recording contact was additionally

set two contacts basal to the masker. In this subset of five subjects the measurements were repeated with

the probe position fixed and the masker position varied. Subjects for all subsets were chosen on the basis of

chronological order and included both children and adults.

Both selectivity and scanning measures were performed at three points along the array. Measurements were

obtained at an apical electrode (EA, electrode 3 or 4), a middle position (EM, electrode 7, 8, or 9), and a

basal position (EB, electrode 13, 14, or 15). Additionally, for all methods and electrode contact positions,

measurements were performed at three different current levels. The effect of masker and probe levels were

compared between the current ranges: low (0.6–0.8 mA), medium (0.9–1.0 mA), and high (1.2 mA). Note

that these measurements could only be performed in patients under general anesthesia, as even the “low”

level used is in the upper range of the electrical dynamic range found in normal clinical practice M-levels.

This is due to an inherent noise limitation of current eCAP recording systems, which do not allow SOE

measures to be made at stimulus levels around subjective thresholds.

Parameter Manipulations in SOE (eCAP)

467

ng the array,

er to investi-

ts of the indi-

in our study

pare the two

measure SOE

the Advanced

t group. More

ters that limit

xcitation area

nd selectivity

ording param-

obe electrode

f the stimulus.

he position of

probe position

ition variable,

or alternating

or correlation

ch perception

, using linear

subjects were

’ HiRes 90K

ay, which has

ics are shown

AP measure-

ry. Using the

software, test

for the record-

rameters used

ic first; pulse

s, sampling

d be observed

measurement

BEDCS intra-

rtant to notice

not essentially

imulating one

t) and record-

ions along the

d for artefact

ating polarity

mulating elec-

ating polarity

ested with the

vity measure-

Selectivity easures (Figure 1, B) were obtained by using a tra-

ditional forward masking technique as described previously (Cohen

et al, 2003). All subjects were tested with the masker contact fixed

and eCAP amplitudes measured for different probe electrode posi-

tions, which were stimulated after a 500

s interval. Raw wave forms

are shown in Figure 1, D. The recording electrode contact was set two

contacts apical to the fixed mask r contact (as Abb s et l, 1999) and

in five patients the recording contact was additionally set two con-

tacts basal to the masker. In this subset of five subjects the measure-

ments were repeated with the probe position fixed and the masker

pos tion varied. Subjects for all subsets we e chosen on the basis of

chronological order and included both children and adults.

Both selectivity and scanning measures were performed at three

points along the array. Measurements were obtained at an apical

electrode (EA, electrode 3 or 4), a middle position (EM, electrode

7, 8, or 9), and a basal position (EB, electrode 13, 14, or 15). Addi-

tionally, for all m thods and electrode contact positions, m asure-

ments were performed at three different current levels. The effect of

masker and probe levels were compared between the current ranges:

low (0.6–0.8 mA), m dium (0.9–1.0 mA), and high (1.2 mA). Note

that these measurements could only be performed in patients under

general anesthesia, as even the “low” level used is in the upper range

of the electrical dynamic range found in normal clinical practice

M-levels. This is due to an inherent noise limitation of current eCAP

recording systems, which do not allow SOE measures to be made at

stimulus levels around subjective thresholds.

Table 1.

A: Patient demographics. B: The numbers of subjects per

scanning measure are shown using the forward masking artefact

rejection scheme and with the alternating polarity artefact rejection

method. For selectivity measures the numbers of subjects are shown

where the position of the masker or probe electrode was fixed, and

which recording electrode was used relative to the probe

electrode.

Patient demographics

Age (years)

35 (average range 1–86)

Duration of deafness (years)

9.8 (average range 0.1–47)

Sex

16 male / 15 female

Child/Adult

12 C / 19 A

Implant type

HiRes 90K HiFocus 1J

Aetiology

progressive/congenital (17),

meningitis (8), rubella (2), trauma (2),

sudden idiopathic (1) and

osteogenesis imperfecta (1)

Measure

Modification

Subjects (n)

Scanning

Forward masking

Alternating polarity

Selectivity

Masker position fixed,

recording 2 contacts apical

Masker position fixed,

recording 2 contacts basal

Probe position fixed,

recording 2 contacts apical

Probe position fixed,

recording 2 contacts basal