A Summary Of Interaural Level Differences

Humans spend most of their daily listening time in an environment that contains multiple sound sources. One aspect that allows normal-hearing listeners to determine the direction of sounds and to supress background noise is the comparison of acoustic information received from the two ears (i.e. binaural hearing). Binaural hearing provides the most important cues in the form of differences in the arrival time of sounds at the two ears (interaural time differences; ITDs) and differences in the level of sounds at the two ears (interaural level differences; ILDs). Both ITDs and ILDs allow normal-hearing listeners to perform auditory tasks such as sound localisation (i.e. determining the locations of sound sources) and sound segregation (i.e. distinguishing

CIs are successfully provided to adults and children who are severely-to-profoundly deaf in order to restore part of their hearing function. Although CI users generally acquire good speech perception in quiet situations, they still face difficulties in performing more challenging listening tasks, such as sound localisation and speech perception in noisy environments. These difficulties are related to the shortcomings of CI technology in mimicking all the capacities of the normal auditory system. When a single CI (i.e. a unilateral CI) is used, an additional limitation is introduced in the form of the inability to use the binaural cues that normal-hearing listeners use to localise sounds and to understand speech in noise. Therefore, there has been a growing interest in providing bilateral CIs (one in each ear) rather than just

In such a system, the speech processor receives signals from both microphones and then processes them simultaneously but independently in two signal processing lines. Given that the sounds are still processed independently between the two ears, it is unlikely that this system would provide benefits for bilateral CI users above those of the conventional bilateral CIs where two independent processors are used. Prior to starting this project, to this researcher’s knowledge, no study on binaural benefits with this kind of cochlear implant has been conducted. However, two studies have since been published over the time span of this project (Verhaert et al., 2012; Bonnard et al., 2013). Both studies reported that adults with synchronised bilateral CIs performed similarly to users of conventional bilateral CIs on sound localisation and speech perception in noise. Verhaert et al. (2012) also reported a significantly better performance for the synchronised bilateral CI subjects when listening with both implants than when one implant was deactivated, which led them to suggest that the DSPB implant subjects can take advantage of binaural cues that are not available when either implant is