Proefschrift_vd_Beek

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.

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. 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,

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

4

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 Std. Dev. Selectivity Mean Std. Dev. Significance

8.2 4.0

6.8 1.1

5.9 2.4

9.0 3.6

5.3 3.5

6.3 2.5

3.3 1.8

4.2 2.8

p

p

p 0.01

p

0.01

0.1

0.01

79