Sound localization is an auditory skill that allows identification of an acoustic signal in space. It's dependent on two mechanisms; a peripheral mechanism that includes signal comparison between right and left ears of a normal hearing person and a central processing mechanism in the brain stem pathways.
Hearing loss impairs both peripheral and central mechanisms. However, people with unilateral hearing loss have some ability to localize sound, a finding that reinforces the importance of monaural spectral cues for this purpose. Monaural ability to localize sound might be especially important for patients with unilateral cochlear implants, who base their ‘acoustic picture' on limited acoustic data.
Speech is a complex acoustic signal that is rich in both spectral and temporal features. The listener makes use of whatever spectral or temporal cues are available to help decode the incoming speech signal. Multiple redundant acoustic cues can contribute to the perception of a single phonemic contrast.
CI processing preserves the slowly varying temporal envelope information in the speech signal (i.e., cues related to amplitude changes over time) but provides only a coarse representation of the spectral envelope.