Adaptation to Distorted Frequency-to-Place Maps: Implications of Simulations in Normal Listeners for Cochlear Implants and Electroacoustic Stimulation

Abstract

The ideal cochlear implant electrode array positioning enables stimulation over a range of cochlear positions whose characteristic frequencies cover the frequency range of speech and match the speech processor filter frequencies. However, the electrode positions achieved in practice may not meet this specification. Users of conventional monaural cochlear implants seem able to perceptually adapt to a mismatch of speech processor filters to electrode positions. In electroacoustic stimulation, it is important to consider possible inconsistencies between acoustic and electrical frequency-to-place mapping. Two simulation studies are outlined that address normal listeners’ ability to perceive speech presented through distorted frequency maps. The first presented a map that is spectrally warped around a 10-mm medial cochlear area. Listeners were able to adapt to this map after a few hours of training. The second study presented a binaural mapping in which one ear was subject to a 6-mm basalward shift. Here listeners were unable to learn to integrate speech information across the two mismatched ears, rather they seem to learn to ignore the shifted information. Frequency-to-place mapping is likely to be an important factor in the successful use of a combination of electrical and acoustic hearing.