Horizontal-Plane Localization of Noise and Speech Signals by Postlingually Deafened Adults Fitted With Bilateral Cochlear Implants*

Abstract

In agreement with previously reported data, subjects with bilateral cochlear implants localized sounds in the horizontal plane remarkably well when using both of their devices, but they generally could not localize sounds when either device was deactivated. They could localize the speech signal with slightly, but significantly better accuracy than the noise, possibly due to spectral differences in the signals, to the availability of envelope ITD cues with the speech but not the noise signal, or to more central factors related to the social salience of speech signals. For most subjects the remarkable ability to localize sounds has stabilized by 5 mo after activation. However, for some subjects who perform poorly initially, there can be substantial improvement past 5 mo. Results from Experiment 2 suggest that ILD cues underlie localization ability for noise signals, and that ITD cues do not contribute.

Lateralization of Interimplant Timing and Level Differences in Children Who Use Bilateral Cochlear Implants

“…Poorer abilities using ITDs than ILDs observed in the CI group is consistent with previous literature involving adult bilateral cochlear implant users (Grantham et al 2008;Grantham et al 2007;Laback et al 2004;Seeber and Fastl 2008;van Hoesel and Tyler 2003).…”

“…This improvement has been widely attributed to detection of inter-implant level differences (Grantham et al 2008;Grantham et al 2007;Laback et al 2004;Seeber and Fastl 2008;Senn et al 2005;Van Hoesel et al 2002).…”

“…Likewise, research that has used direct stimulation of participants' CIs, as opposed to free-field localization, revealed ITD thresholds of up to an order of magnitude greater than their normally hearing counterparts (Lawson et al 1998;van Hoesel 2004). Many have suggested, therefore, that ITDs contribute minimally to sound localization in bilateral CI users under everyday listening conditions (Grantham et al 2007). …”

Restoring hearing symmetry with two cochlear implants or one cochlear implant and a contralateral hearing aid

“…In general and compared with unilateral implant conditions, adult recipients of bilateral implants perform fairly well in localization tasks in the horizontal plane [75,78,[84][85][86][87][88][89][90][91][92][93]. For example, in five subjects using pink noise bursts presented from eight loudspeakers that spanned 108°, unilateral conditions resulted in 20° to 60°R MS errors, but only 10° RMS errors were noted for bilateral conditions [93].…”

Adjustments of the amplitude mapping function: Sensitivity of cochlear implant users and effects on subjective preference and speech recognition

“…Bimodal and bilateral CI users show variability in their ability to localize sound sources in the horizontal plane, and in general both have better access to inter-aural level differences (ILDs) than inter-aural timing differences (e.g. Aronoff et al, 2010;Francart et al, 2011;Grantham et al, 2007;Schoen et al, 2005;Van Hoesel & Tyler, 2003). AMF adjustments may affect loudness growth for input sound signals and thereby the loudness balance between ears across the DR. With respect to bilateral CI users, Goupell et al (2013) showed that bilateral loudness equalization does not necessarily produce a centered auditory image or optimal lateralization.…”