Does Onset Enhancement Improve Availability of Envelope ITDs in Cochlear Implant Users?

Introduction Auditory scene analysis (ASA) is the process by which the auditory system detects, identifies and tracks sounds coming from a certain position in a mixture of different sounds (i.e. multiple talkers, noise, reverb). The auditory system makes use of location, pitch, temporal onset and common modulation cues. Cochlea implant (CI) users do not rely on pitch cues for segregation and therefore we propose that location cues are of greater importance. Reduced access to binaural cues (i.e., interaural time differences [ITD]) in the temporal fine structure (TFS) limits sound localization ability in CI users [4]. Kerber and Seeber (2013) [2] showed that localization performance in reverberation of CI users is correlated with their ability to make use of envelope ITDs (envITD). Monaghan et al. (2013) [3] showed that saliency of envITDs can be improved by increasing modulation depth, steepness of the rising slope and interaural coherence. Seeber and Monaghan (2013) [6] developed a stimulation strategy where selective enhancement of envITDs based on the direct-to-reverberant ratio (DRR) could improve localization performance in CI users in reverberant spaces. The aim of the present study was to analyse locations of envelope peaks (envpeak) and their relation to the direct-to-reverberant ratio (max DRR) for speech sounds in two different rooms to identify the favourable time points in the envelope that provide most information about the ITD of the direct sound and to test the respective outcomes in a lateralization and speech test.