Proefschrift_vd_Beek

phoneme scores over the headpiece microphone was already noticeable at 10 dB SNR: from 71% to 80% and 77% with the Handymic ( p = 0.11) and the Linkit respectively ( p = 0.36). At an SNR of 0 dB, the phoneme scores for the Handymic and the Linkit were 67% and 62% respectively for all subjects, the word scores were 44% and 38% respectively. At –5 and –10 dB, fewer subjects were involved. For the Handymic, the phoneme scores were 55% and 45% at –5 and –10, while the Linkit results equalled 54% and 39%. Comparison of SRT and Benefit The mean SRT values for the Handymic and the Linkit were significantly better than the SRT value obtained with the headpiece ( p < 0.001, Students t -test). The lower average SRT value of the Handymic over the Linkit was not significant ( p = 0.3). The results in Figure 5 show that the average benefit of the Handymic and Linkit over the headpiece equals 8.2 dB (SD = 2.6) and 5.9 dB (SD = 3.9) respectively. Of the subjects, 12 out of 13 received a positive benefit from listening with the Handymic or the Linkit. However, the results of subjects C and K are considerably different in comparison to the results of the other subjects and also beyond expectations based on the technical properties of the directional microphones. Subject C had a phoneme score in quiet surroundings of 67% prior to the testing. Her test results in quiet surroundings in this study were equal for all three microphones (67– 69%). For this subject, the intelligibility was immediately affected by the noise at SNR +10 dB. The scores went down to 51, 56 and 44% for the headpiece, the Handymic and the Linkit respectively. However, at SNR +5 and 0 dB, the scores were not yet reduced to the chance-level of the CVC material (being equal to 10%). At 0 dB, scores were maintained at 35, 34 and 43% respectively. Most likely, results for subject C were influenced by the shallow TABLE 3. Test results of normal hearing (NH) and cochlear implant users in diffuse noise set-up Phoneme scores at SNR (%) in set-up Word-scores (%) Ear/Microphone Quiet 15 dB 10 dB 5 dB 0 dB 5 dB 10 dB 15 dB 0 dB NH/none [ N 5] 100 — 100 — 93 — 67 42 81 CI/Headpiece 87 59 [1] 71 54 [5] 42 32 [6] — — 21 CI/Handymic 85 — 80 48 [1] 67 55 [11] 45 [7] 31 [2] 44 CI/Linkit 86 53 [1] 77 56 [1] 62 54 [11] 39 [8] 33 [1] 38 Standard deviations (%) NH/none 0.4 0.5 1.4 3.4 CI/Headpiece 8 14 17 12 CI/Handymic 9 11 15 18 CI/Linkit 9 14 13 15 Implant users used their own processor with the Linkit or Handymic connected to the audio input. The mean phoneme scores on the CVC word test (65 dB SPL, free field, 44 words per data-point) in quiet surroundings and in background noise with SNRs of 15, 10, 5, 0, 5, 10 and 15 dB. The mean values are given per SNR for 13 subjects. The numbers between the brackets denote the number of cochlear implant users that was tested at 15, 5, 5, 10 and 15 dB. The last column gives the word score at SNR 0 dB as a comparison.

2

TABLE 3. Test results of normal hearing (NH) and cochlear implant users in diffuse noise set-up

Phoneme scores at SNR (%) in set-up

Word-scores (%)

Ear/Microphone

Quiet

15 dB 10 dB 5 dB 0 dB

5 dB

10 dB 15 dB

0 dB

NH/none [ N CI/Headpiece CI/Handymic

5]

100

— 100

— 93

— 67

42

81 21 44 38

59 [1]

54 [5] 48 [1] 56 [1]

32 [6]

87 85 86

71

42 67 62

—

—

55 [11] 54 [11]

45 [7] 39 [8]

31 [2] 33 [1]

— 80

53 [1]

CI/Linkit

77

Standard deviations (%)

NH/none

0.4

0.5

1.4

3.4

CI/Headpiece CI/Handymic

8 9 9

14 11 14

17 15 13

12 18 15

CI/Linkit

Implant users used their own processor with the Linkit or Handymic connected to the audio input. The mean phoneme scores on the CVC word test (65 dB SPL, free field, 44 words per data-point) in quiet surroundings and in background noise with SNRs of 15, 10, 5, 0, 5, 10 and 15 dB. The mean values are given per SNR for 13 subjects. The numbers between the brackets denote the number of cochlear implant users that was tested at 15, 5, 5, 10 and 15 dB. The last column gives the word score at SNR 0 dB as a comparison. Implant users used their own processor with the Linkit or Handymic connected to the audio input. The mean phoneme scores on t e CVC word test (65 dB SPL, free field, 44 words per data-point) i quiet surroundings and in background noise with SNRs of 15, 10, 5, 0, 5, 10 and 15 dB. The mean values are given per SNR for 13 subjects. The numbers between the brackets denote the number of cochlear implant users that was tested at 15, 5, 5, 10 and 15 dB. The last column gives the word score at SNR 0 dB as a comparison.

TABLE 4. SRT values based on linear interpolation between near points and curve fitting for whole group of data

Linear interpolation

Curve fitting

Ear/Microphone

SRT (SD) in dB

Gradient %/dB

SRT (SD) in dB

Gradient %/dB

NH/none

13.4 (0.6) 2.5 (4.8) 5.7 (5.2) 3.4 (6.3)

5.0 4.6 4.7 3.9

—

—

CI/Headpiece CI/Handymic

2.6 (4.8) 5.4 (5.3) 3.2 (6.6)

5.7 5.0 3.9

CI/Linkit

SRT values and gradients are averaged based on each individual SRT and gradient. SRT values and gradients are averaged based on each individual SRT and gradient.

31