Models of the electrically stimulated binaural system: A review

ABSTRACT

In an increasing number of countries, the standard treatment for deaf individuals is moving toward the implantation of two cochlear implants. Today’s device technology and fitting procedure, however, appears as if the two implants would serve two independent ears and brains. Many experimental studies have demonstrated that after careful matching and balancing of left and right stimulation in controlled laboratory studies most patients have almost normal sensitivity to interaural level differences and some sensitivity to interaural time differences (ITDs). Mechanisms underlying the limited ITD sensitivity are still poorly understood and many different aspects may contribute. Recent pioneering computational approaches identified some of the functional implications the electric input imposes on the neural brainstem circuits. Simultaneously these studies have raised new questions and certainly demonstrated that further refinement of the model stages is necessary. They join the experimental study’s conclusions that binaural device technology, binaural fitting, specific speech coding strategies, and binaural signal processing algorithms are obviously missing components to maximize the benefit of bilateral implantation. Within this review, the existing models of the electrically stimulated binaural system are explained, compared, and discussed from a viewpoint of a “CI device with auditory system” and from that of neurophysiological research.

KEYWORDS:

• Auditory system
• binaural system
• cochlear Implant
• brainstem

Acknowledgements

I thank Swantje Suchland from the DFG Cluster of Excellence “Hearing4All” for drawing Figure 1, Yoojin Chung for providing Figure 2 and valuable help with the MSO models, and Ian Bruce for various excellent comments on a draft version of this manuscript including the AN fiber latency variability hypothesis. I thank Daryl Kelvasa for improving the model’s ease of use and for his effort to make it openly available as part of the Auditory Model Toolbox.

Funding

This research was undertaken, in part, thanks to funding from the Canada Research Chairs program.

Additional information

Funding

This research was undertaken, in part, thanks to funding from the Canada Research Chairs program.