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scanning and 14% for selectivity). The curves that did not meet the 0.6 criterion were set as the limit of the
array in the apical or basal direction (as per Abbas et al, 2004).
Descriptive statistics, showing the means and differences of scanning and selectivity along the array, are
summarized in Table 2. The calculated linear mixed model, containing data of 31 different subjects (for 26
subjects, measures of both scanning and selectivity were obtained, for three subjects only scanning data, and
for two subjects only selectivity measurements), confirmed differences in the width of curves obtained using
the two methods. Scanning produced significantly wider curves than selectivity (mean 7.4 contact spacing
(SE 0.26) vs. 4.7 spacing (SE 0.27),
p
< 0.01). An example of scanning and selectivity curves in a typical
subject is shown in Figure 4, A. The influence of the method was largest for basal and apical contacts and
less prominent for the middle contact in the apical direction (Table 2). No factor associated with the outliers
as seen in Figure 3 could be identified.
Comparison along the array
A second linear mixed model was constructed that included only the selectivity measurements (i.e. excluding
the scanning data) of 28 subjects in order to examine the effect of stimulating electrode contact position on
this SOE measure. This model confirmed the differences in curve width along the array for the selectivity
measure as shown in Table 2. The curves of EM-A were the widest, followed by the EA-B, EB-A, and
EM-B. Taking EA-B as a reference, EM-A was 1.0 contact spacing wider (SE = 0.38,
p
= 0.01), EM-B was
2.0 contacts narrower (SE = 0.38,
p
< 0.01), and EB-A was 1.2 contacts narrower (SE = 0.41,
p
< 0.01).
These effects are illustrated in Figure 2, which shows a typical example in an individual patient. Levels of
significance for the differences found are shown in Table 3.
60% of the
width of the
r the highest
nalysis with
easurements
s correlation
ect to be the
n mean, and
(e.g. subject
ons between
fixed, popu-
mean) gen-
Using linear
h parameter
parameters.
ll data, even
et al, 2004).
t mixed lin-
chnique, the
significance
f descriptive
in boxplots.
etely match-
missing data
inear mixed
bjects tested
ersus selec-
f selectivity
e recording
ker or probe
tion method
r model was
as compared
al recording
ible to take
the current level and location along the array into account in the
analysis with speech data.
Results
Comparison of scanning vs. selectivity
Figu e 3 shows boxplots for scanning (upper p nels) and selectivity
(lower panels) measures at the apical (EA-B), middle in apical and
basal directions (EM-A and EM-B respectively), and basal (EB-A)
electrodes, measured at three different current levels (low, medium,
and high).
The majority of curves (95% for selectivity and 75% for scanning)
met the 0.6 criterion. However, for the curves of the middle electrode
contact in the pical direction th s c it ion w s often not met (42%
for scanning and 14% for selectivity). The curves that did not meet
the 0.6 criterion were set as the limit of the array in the apical or
basal direction (as per Abbas et al, 2004).
Descriptive statistics, showing the me ns and differen es of
scanning and selectivity along the array, are summarized in Table 2.
The calculated linear mixed model, containing data of 31 dif-
ferent subjects (for 26 subjects, measures of both scanning nd
selectivity were obtained, for three subjects only scanning data,
in response to stimulation at the apical electrode contact (EA, left), middle contact
show the normalized response amplitudes recorded from locations along the array,
(solid line) current levels, together with the 0.6 criterion line. The width of the curve
.6 line (indicated by arrows) for apical electrode in basal direction (EA-B), middle
and basal electrode in apical direction (EB-A). The location of electrode of interest
curve meets the 0.6 criterion (dotted line over half figure height) are indicated.
Table 2.
Descriptive statistics including mean widths in terms of
electrode contacts for scanning (top rows) and selectivity (lower
rows) for the different electrode contact locations (with standard
deviations). Significance levels are shown in the bottom row. Data
shown are descriptive statistics and are incorporated in the linear
mixed model for further analysis of separate parameters, which are
described in the Results section.
EA-B
EM-A
EM-B
EB-A
Scanning
Mean
8.2
6.8
5.9
9.0
Std. Dev.
4.0
1.1
2.4
3.6
Selectivity
Mean
5.3
6.3
3.3
4.2
Std. Dev.
3.5
2.5
1.8
2.8
Significance
p
0.01
p
0.1
p
0.01
p
0.01