A critical review of work on speech analyzing hearing aids

Attempts to develop special aids for speech communication and speech correction of severely hard-of-hearing or totally deaf persons have been going on since the beginning of the 1920's. For information transmission, the auditory, tactual, and visual senses have been used. These aids have in many cases been called "sensory aids for the deaf" in analogy with the "sensory aids for the blind" that make it possible for the blind to read ordinary letters, perceive obstacles, and so on. Recently, the name "speech analyzing aids" has been suggested, which seems to be more adequate, as some types of speech analyzing techniques are used in contrast to the linear amplification used in most ordinary hearing aids. In the development of "speech analyzing aids for the deaf" two problems must be considered: 1) Which elements of the speech signals ought to be automatically extracted and transmitted to the deaf subject? 2) What kind of signals and which sense modality shall be used for the transmission of the extracted speech information? Speech is learned by imitation which means that an efficient aid for speech perception also can be used for speech learning. However, in several respects it is better to treat aids for speech correction and speech perception as separate problems. Here, for the most part, only aids for speech perception will be discussed. An attempt will be made to summarize the development in this area and to discuss published results from experiments with different types of equipment. Some suggestions for future experiments will be given.