Lateralization of interaural level differences in children with bilateral cochlear implants

Figures & data

Table 1 Subject characteristics.

Subject	Age at testing (yrs; mos)	Age at CI1 (yrs; mos)	Duration of BiCI use (yrs; mos)	Age at CI2 (yrs; mos)	Inter-implant delay (yrs; mos)	HA scores (prior to CI2) (%)	PTA250/500Hz (prior to CI2) (dB HL)	Etiology
S26	12;02	2;06	3;6	8;08	6;02	54	85.0	Pneumococcal meningitis
S8	15;08	11;06	1;8	14;00	2;06	75	70.0	Hereditary
S18	10;05	3;01	3;3	7;02	4;00	54	77.5	Unknown
S5	15;01	3;04	1;6	13;07	10;03	60	70.0	Unknown (enlarged vestibular aquaducts)
S28	17;09	1;11	1;6	16;03	14;03	75	45.0	Pneumococcal meningitis
S32	12;08	6;00	3;3	9;05	3;05	63	25.0	DFNB8/10
S11	11;04	7;02	2;2	9;02	2;00	87	57.5	Pendred syndrome
S21	15;03	1;05	13;10	1;05	0;0	NA	NA	Pneumococcal meningitis
S33	10;02	0;10	9;4	0;10	0;0	NA	NA	Pneumococcal meningitis

BiCI, bilateral cochlear implant; CI1, first cochlear implant; CI2, second cochlear implant; HA, hearing aid; NA, not applicable; mos, months; PTA, pure tone average; yrs, years.

Figure 1 An example of an ILD psychometric curve as described by Equation (1). The $\theta T$ is the perceptual bias or shift in decibels, with a negative value indicating a shift towards the right or CI1 side and a positive value indicating a shift towards the left or CI2 side. In this example, a shift of −1.25 dB is shown, indicating no clear bias. The grey shaded zone indicates the width or $\omega T$ in decibels, which denotes the 10–90% width of the sigmoid. In this example the width is around 10 dB.

Figure 2 ILDs for the different groups and stimulus types (BB, LP, MP and HP). The normal hearing children (NH) are shown at the top (Fig. 2A–D), whereas the sequential (SEQ) and simultaneous (SIM) BiCI children are respectively shown in the middle (Fig. 2E–H) and bottom (Fig. 2I–L) of the figure. The grey lines within the plots describe the individual results, whereas the bold lines indicate the mean for that particular group. For the NH and SEQ groups, the mean shift (θ) and width (ω) are depicted. For the SIM children, the individual values are listed. A negative value indicates an ILD towards the right or CI1 side and a positive value indicates an ILD towards the left or CI2 side. For the children with simultaneous BiCIs, no bold line was drawn. With the exception of three children, a steep ILD curve is observed in most children with normal hearing, indicative of good ILD perception.

Figure 3 Scatterplot of ILD width (ω_ILD) against shift (θ_ILD) for the different groups and stimulus types. A negative shift corresponds with a shift towards the right or CI1 side and a positive shift is a shift towards the left or CI2 side. No significant difference in ILD width between groups was found (p > .05). Compared to the children with normal hearing, children with sequential BiCIs showed a significant larger shift towards the CI1 side for the BB stimulus (Figure 3A), but not for the other stimulus (p < .05).

Figure 4 Scatter plot with inter-implant delay depicted against ILD shift (θ_ILD) for the children with BiCIs. There is a significant negative correlation between inter-implant delay and the ILD shift for both the BB and the HP stimulus.

Figure 5 Scatterplot of ILD shift (θ_ILD) against the target bias (bT) in localization for the different groups and stimulus types. In this Figure can be seen that when a shift in ILD is higher than 5 dB to the CI1 or CI2 side for the children with BiCIs, this shift is also seen in localization for S26 and S11, but not for S28.