Hands-Free Devices for Displaying Speech and Language in the Tactile Modality - Methods and Approaches.

Communication is an essential part of human life. In this article, we give an overview of hands-free tactual devices that have been developed and tested for conveying speech or language. We opted for "hands-free" because especially in the case of individuals with impaired vision, in many situations their hands will be occupied with other essential tasks. We start this survey with presenting the various word building blocks that have been tested. These blocks vary from units based on the actual speech signal, via patterns representing phonemes, to letters, or letters coded via Morse or Braille-like patterns. In the second part of this article, studies that use these building blocks to create words are discussed. General findings are that successful devices do not necessarily depend on underlying speech characteriscs, dynamic patterns give better results than static patterns, and more vibrators do not generally give better results. Moreover, some of the most successful devices required only limited training time. Most of the recent devices are still in a quite early state of development and are tested only with a limited number of patterns. However, many of these recent devices give promising results and are worthwhile to further investigate and develop.