The Fitting of Hearing Aid Instruments

Abstract

As of now there is no generally accepted, credible method of validating the use value of a hearing-aid fitting. Since the development of the modern hearing aid, the fitting of a hearing prosthesis has been basically an art form. The acceptance of most hearing-aid fittings is judged by the subject, the built-in biases of the clinician, or the hearing-aid dispenser. The current, basic method of assessing the efficiency of hearing-aid use stresses some form of speech discrimination. Speech discrimination does not depend solely upon the acoustical contribution of the hearing prosthesis. There are many factors contributing to the recognition of a speech signal other than the hearing-aid response. The following is a short list of the more prominent causes for the deterioration of speech discrimination skills. 1. A prolonged hearing loss would cause a memory regression that contributes to errors, leading to erroneous scoring. 2. The speech material used may be unfamiliar to the listener (unfamiliar words and sounds will contribute to discrimination error because they are difficult to recognize). 3. Because of a learning process, the initial discrimination scores may be lower and not indicative of the final discrimination ability following hearing-aid use. 4. Different regional dialects within the same language code may contribute to errors of discrimination. 5. The difficulty of word lists vary, causing differences of discrimination scores relative to the per cent of correct identification. 6. Congenitally deaf individuals and persons foreign to our language system cannot be evaluated with conventional word lists. Because of the foregoing and other variables, it appears evident that speech testing is not a sufficiently reliable and repeatable method of validating the effectiveness of a hearing prosthesis. Barfod (1979) described an auditory, psychologic interface and analyzes the basic reasoning that interferes with speech validation of a hearing prosthesis, at the time of initial fitting. The classic work of Shore, Bilger, and Hirsh (1960) underscored the lack of reliability and repeatability of measurements when phonetically balanced words are used for