Unilateral spectral and temporal compression reduces binaural fusion for normal hearing listeners with cochlear implant simulations

Abstract

Patients with single sided deafness have recently begun receiving cochlear implants in their deaf ear. These patients gain a significant benefit from having a cochlear implant. However, despite this benefit, they are considerably slower to develop binaural abilities such as summation compared to bilateral cochlear implant patients. This suggests that these patients have difficulty fusing electric and acoustic signals. Although this may reflect inherent differences between electric and acoustic stimulation, it may also reflect properties of the processor and fitting system, which result in spectral and temporal compression. To examine the possibility that unilateral spectral and temporal compression can adversely affect binaural fusion, this study tested normal hearing listeners' binaural fusion through the use of vocoded speech with unilateral spectral and temporal compression. The results indicate that unilateral spectral and temporal compression can each hinder binaural fusion and thus may adversely affect binaural abilities in patients with single sided deafness who use a cochlear implant in their deaf ear.

Figure 1

Schematic illustration of the conditions for Experiment 1 showing the relative time and center frequency for each vocoded condition (color online).

Figure 2

The effect of spectral and temporal compression on binaural fusion. Bars indicate 20% trimmed means and error bars indicate the winsorized standard error.

Figure 3

Schematic illustration of the conditions for Experiment 2 showing the amount of spectral compression for various simulated array lengths. This reflects a cochlear duct length of approximately 35mm.

Figure 4

The effect of spectral compression on binaural fusion when both ears are receiving vocoded signals. Bars indicate 20% trimmed means and error bars indicate the winsorized standard error.

Figure 5

The relationship between the average mismatch between ears (in mm) and percent fusion. Each point represents the 20% trimmed mean for a given condition. The line indicates the fit based on a mixed effect regression.

Figure 6

The effect of spectral compression on binaural fusion when one ear is receiving an unprocessed signal and the other ear is receiving a vocoded signals. Bars indicate 20% trimmed means and error bars indicate the winsorized standard error.