1. Figures for Chapter 14 Binaural and bilateral issues Dillon (2001) Hearing Aids

2. Figure 14.1 Variation of the source direction in the horizontal plane. Near earFar ear Source: Dillon (2001): Hearing Aids Horizontal localization

3. Inter-aural time differences Figure 14.2 Interaural time difference for low-frequency sounds as a function of direction measured from directly in front. Data are the average of measurements on people and on a manikin (Kuhn, 1982). Source: Dillon (2001): Hearing Aids

4. Figure 14.3 Interaural level difference for three source directions in the horizontal plane. Data are calculated from Shaw (1974). Interaural level differences are zero for frontally incident sound. Source: Dillon (2001): Hearing Aids Inter-aural level differences

5. Figure 14.4 Variation of the source direction in the vertical plane. Source: Dillon (2001): Hearing Aids Vertical localization

6. Figure 14.5 Head diffraction effects from the undisturbed field to the eardrum for five source directions in the horizontal plane, with positive angles representing sound arriving from the side of the ear in question. Data are from Shaw (1974). Source: Dillon (2001): Hearing Aids Head diffraction

7. S N 30 o 60 o SNR increased by 11 dB at 3 kHz, and by 9 dB averaged across frequency SNR decreased by 9 dB at 3 kHz, and by 8 dB averaged across frequency Figure 14.6 Effect of head diffraction on the SNR at each ear, relative to the SNR in the undisturbed field. The SNR at the right ear is thus 20 dB better than at the left ear at 3 kHz, and 17 dB better when averaged across frequency. Source: Dillon (2001): Hearing Aids Effect of head diffraction on SNR

8. Signal Noise ++ Figure 14.7 Waveforms at the left and right ears when noise arrives from directly in front and a signal (in this case a pure tone) arrives from one side. LeftRight Source: Dillon (2001): Hearing Aids Inter-aural time differences

9. S N Bilateral Fitting Unilateral Fitting S N Figure 14.8 Test arrangement for demonstrating bilateral advantage, showing the location of the speech (S) and noise (N) loudspeakers. Speakers should be 0.5 m or more from the patient. For unilateral fittings to the left ear, the S and N sources should be reversed for both the bilateral and unilateral tests. Source: Dillon (2001): Hearing Aids Demonstrating binaural advantage

10. Bilateral Fitting Unilateral Fitting Figure 14.9 Test arrangement for detecting negative binaural interactions. Speech and noise both come from the same loudspeaker. Source: Dillon (2001): Hearing Aids Detecting negative binaural interactions

11. Figure 14.10 An audiogram for a person who is likely to benefit from the hearing aid cross-over effect if a bilateral fitting is provided. 2501255001k2k4k8k 0 20 40 60 80 100 120 Frequency (Hz) Hearing threshold (dB HL) Source: Dillon (2001): Hearing Aids Binaural cross-over effect

12. 2501255001k2k4k8k 0 20 40 60 80 100 120 Frequency (Hz) Hearing threshold (dB HL) Figure 14.11 An audiogram where the poorer ear should be aided if the person chooses to have a unilateral fitting. Source: Dillon (2001): Hearing Aids Poorer ear fitting

13. 2501255001k2k4k8k 0 20 40 60 80 100 120 Frequency (Hz) Hearing threshold (dB HL) Figure 14.12 An audiogram where the better ear should be aided if the person chooses to have a unilateral fitting. Source: Dillon (2001): Hearing Aids Better ear fitting