Hearing Aids   by Dr. Allan S. Mehr, FAAA Private Practice Salem, OR Dr. Robert W. Sweetow, FAAA University California San Francisco, CA   Hearing aids are mini instruments designed to amplify sound. Hearing aids collect sound from the environment, amplify them, and direct this amplified signal into the user's ear. A hearing aid evaluation is necessary in order to select the hearing aid(s) that is/are most appropriate for a given individual. Unless otherwise indicated, binaural instruments tend to provide superior benefit compared to monaural hearing aid(s) and thus are usually recommended.   There are many different types of hearing aids on the market. When an individual is considering purchasing a hearing aid(s) there are a number of decisions that need to be made. The two most important decisions are style of hearing aid(s) and circuit options.