101 / 162
99
5
Speech Perception
Speech discrimination scores were obtained during normal clinical follow-up at predetermined intervals.
The data used for analysis in this study were the scores obtained after 1 year of follow-up. For 19 of the 151
subjects included in the study, speech scores at the 1-year follow-up were not available for logistical reasons.
The standard Dutch speech test of the Dutch Society of Audiology, consisting of phonetically balanced
monosyllabic (CVC) word lists, was used [Bosman and Smoorenburg, 1995]. As described previously [van
der Beek et al., 2005], the speech material was presented in free field in quiet at a level of 65 dB.
Statistical Analysis
All data analysis was performed using SPSS 19.0 (IBM, Armonk, N.Y., USA). Mixed linear models were
used to analyze the data and to construct predictive models. These models aimed to predict Tand M-level
profiles using only one measured level at one fixed individual electrode contact. In a mixed linear model,
responses from a subject are thought to be the sum of fixed and random effects. The effects which affect the
population mean are called fixed. If an effect is associated with a sampling procedure (e.g., subject effect), it
van der Beek/Briaire/Frijns
Audiol Neurotol 2015;20:1–16
DOI: 10.1159/000362779
6
Results
Figure 1 shows the percentiles for T-levels (fig. 1a), M-
levels (fig. 1b) and DRs (fig. 1c) at the 1-year follow-up.
Data are presented in clinical units to enable comparison
of levels w th differe t pulse widths. T-levels, M-levels as
well as DRs showed an increase towards the basal end.
The T-levels reflected real measurements of the individ-
ual levels at each individual electrode contact, whereas
the M-levels were set for the subject using a profile fitting
method with emphasis on the higher frequencies.
The ratio of T-/M-level is shown in a box plot in figure
2a. The median T-/M-level ratio for all the electrode duos
was between 20 and 35%, corresponding to a DR of 9–14
dB. The whiskers are located at 1.5 × interquartile range
(IQR). A 10% or smaller r tio only occurred in a very lim-
10
20
30
40
50
60
70
80
90
100
0
T-/M-level ratio (%)
Electrode duo
a
10
20
30
40
50
60
70
80
90
100
0
0
50
100
150
200
250
T-/M-level ratio (%)
ASM T-level (CU)
b
10
20
30
40
50
60
70
80
90
100
0
100 200 300 400 500 600 700
100 200 300 400 500 600
T-/M-level ratio (%)
ASM M-level (CU)
c
10
20
30
40
50
60
70
80
90
100
0
0
T-/M-level ratio (%)
ASM DR (CU)
d
R
2
linear = 0.367
R
2
linear = 0.180
15+16
13+14
11+12
9+10
7+8
5+6
3+4
1+2
Fig. 2.
a
Box plot of T-/M-level ratio along the array (whiskers at 1.5 × IQR).
⚪
= Outlier;
*
= extreme.
b
Patients’
overall T-level vs. patients’ T-/M-level ratio with the linear fit line.
c
Patients’ overall M-level vs. patients’ T-/M-
level ratio.
d
Patients’ overall DR vs. patients’ T-/M-level ratio with the linear fit line.
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Fig. 2.
a Box plot of T-/M-level ratio along the array (whiskers at 1.5 × IQR).
º
= Outlier; * = extreme. b Patients’ overall T-level vs. patients’
T-/M-level ratio with the linear fit line. c Patients’ overall M-level vs. patients’ T-/M- level ratio. d Patients’ overall DR vs. patients’ T-/M-
level ratio with the linear fit line.