The choice of stimulation strategy affects the ability to detect pure tone inter-aural time differences in children with early bilateral cochlear implantation

Abstract

Objectives: To investigate if the interaural time difference (ITD) ability is dependent of stimulation strategy. To examine the correlation between ITD, interaural level differences (ILD) and the ability to localize different sounds.

Methods: Thirty subjects aged 8–13 who were implanted bilaterally before 3 years of age were tested. Twenty of the subjects used processors programmed with fine structure (FS) strategy on both sides. ITD and ILD just noticeable difference (JND) of a 250 Hz pure tone was measured using their clinical processors. Furthermore, their ability to localize sound in the horizontal plane was measured using eye tracking.

Results: Ten of the 20 subjects with FS obtained an ITD threshold compared to none in the group without FS (0/10). ILD JND was correlated to localization ability of the broadband (BB) sound. Mean absolute error of the localization of a low-frequency (LF) sound was larger than that of a BB sound.

Conclusions: The ability to detect ITD was present only when the cochlear implant stimulation had FS. The LF sound was more difficult to localize than the BB sound and ITD ability of FS strategies did not affect the localization ability of either sound. A low ILD seems necessary to improve the localization ability.

Chinese abstract

目的：调查耳间时间差（ITD）能力是否依赖于刺激方法。检测ITD、耳间水平差异（ILD）和限定不同声音位置的能力之间的相关性。

方法：对3岁以前接受双耳植入的8-13岁年龄段的30名受试者进行测试。其中20位受试者在两侧都使用精细结构（FS）法编程的处理器。使用他们的临床处理器测量出ITD和ILD的可显差异（JND）为250Hz纯音。此外, 他们在水平面上定位声音的能力是使用眼追踪来测量的。

结果：20名使用FS的受试者中有10名获得了ITD阈值, 而没有使用FS的受试者中无人获得（0/10）。 ILD JND与宽带（BB）音的定位能力相关。低频（LF）音定位的平均绝对误差大于宽带音定位的绝对误差。

结论：只有当人工耳蜗植入刺激具有FS时, 才能检测到ITD。 LF音比BB音更难以定位, 而FS法的ITD能力并不影响这两种声音的定位能力。要提高定位能力, 似乎必须具有低ILD。

Keywords:

• Bilateral cochlear implant
• children
• interaural time difference
• ITD
• fine structure
• localization
• CI

Acknowledgements

We are grateful for the participation of the children. We would like to acknowledge Åke Olofsson for programming the presentation system of the localization equipment and Filip Asp for valuable comments.

Disclosure statement

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.

Additional information

Funding

This work was funded by the Tysta Skolan Foundation, the CI fund at Karolinska University Hosptial, the regional agreement on medical training and clinical research (ALF) between Stockholm County Council and Karolinska Institutet, and Karolinska University Hospital.