iCallsign is designed for hearing-impaired individuals who may find it difficult to converse in complex listening environments, for example, a room with noise or multiple talkers. The app provides a system of structured learning that is based on the gradual introduction of the competing voices. One voice is the target voice. One to four alternate voices create the distracting environment. The number and loudness of the distracting voices is determined by the user's level of performance. Visit the iCallsign website for details of the testing procedure.