Cochlear Implants (Cis) are surgically implanted devices that can provide access to the hearing world for individuals with bilateral ‘severe to profound’ hearing loss who do not gain benefit from conventional hearing aids. However, some patients who have received Cis derive more benefit from them than others. There is a relative paucity of work involving those individuals who have had poor outcomes and are performing (with regard to speech understanding) below the level expected for them pre-operatively. The aim of this thesis was to identify potentially remedial factors that contribute to poor performance with a CI, in an attempt to develop practical clinical protocols for the management of ‘poor performers’. Hypotheses: la. The ability to discriminate pitch reliably across the electrode array predicts overall speech discrimination levels in Cochlear Implant users. lb. Using pitch discrimination findings as a ‘site-selection strategy’ would lead to improvements in speech understanding in poor performers. 2. Areas of poor pitch discrimination may correlate with specific electrode position within the cochlea measured by post-operative computerised tomography imaging.