Cochlear implants (CIs) allow many people to re-gain their speech perception. After implantation listeners need to adapt to a very different sensory experience and the CI transmits only parts and patterns of the information that is present in the acoustically rich natural signal. There are individual differences in the success of this adaptation. This study aims at examining causes of individual variation by relating speech processing with CI to models of speech perception in native and non-native listeners. This study will (1) examine how speech processing with CI fits within the architecture of models of speech perception and lexical access. Further, (2) the underlying mechanism of these models will be related to measures of cortical processing, in order to find physiological correlates that can give more objective measures of how new CI users adapt their speech processing to the device. (3) These measures will be applied to examine the course of speech processing in long-term users of CI and to track the progress of adaptation towards the prosthesis in listeners after new implantations. A set of behavioural experiments will examine the representations of speech in CI users. These experiments will be complemented by electrophysiological measures, and an eye-tracking study will examine the course of information processing. Long-term users of CIs will be compared with normal-hearing listeners, and a longitudinal study, run in parallel, will examine the changes in the cortical processing as new CI users adapt to the prosthesis. This study will bring together the insights from the framework of speech perception and word recognition with insights from applied engineering in medical environment. In this way the study will contribute to the frontier research that crosses the disciplines of basic cognitive science and applied technology. The study aims to give a comprehensive perspective on speech processing in CI and to track the way the CI signal maps onto the lexicon.