Evaluating Possible Improvement in Speech and Hearing Tests After 28 Days of Dosing of the Study Drug AUT00063 Compared to Placebo (QuicKfire)

Inclusion Criteria: * Male or female aged ≥ 18 years. * Native English speaking. * Received a unilateral cochlear implant within the last 9 to 48 months for post-lingual deafness. * Less than optimal speech perception at the time of enrolment (defined as a score of 25% to 95% for Bamford-Kowal-Bench (BKB) sentences. * Fully trained and optimised at the time of enrolment. * CI device working satisfactorily and no interventions in the 4 weeks prior to the first dose of study medication. * Signed and dated informed consent. Exclusion Criteria: * Not able to understand and comply with the requirements of the study. * CI undertaken primarily for the management of severe tinnitus. * Moderate or severe depression or generalised anxiety. * Currently taking or planning to take medications that are prohibited by the study protocol. * History of important cardiac, endocrine, pulmonary, neurologic, psychiatric, hepatic, renal, hematologic, immunologic, or other major diseases deemed clinically significant. * Clinically significant ECG abnormality or prolonged QT interval. * Screening laboratory safety test results outside the normal ranges that are deemed to be clinically significant by the investigator. * Any acute disabling illness. * Clinically significant alcohol or drug abuse. * Participation in any clinical research study evaluating another investigational drug or therapy within 30 days or at least 5 half-lives of the investigational drug. * For women: Pregnant or nursing. * For men and women: Not willing or able to use adequate methods of contraception.