Visual Communication Systems for the Deaf

The paper is in two parts. The first (Section II) describes six years´ operating experience with an in-house switched videotelephone system installed in the headquarters of the Royal National Institute for the Deaf, London. The system, which has recently been extended to 10 terminals, has confirmed the usefulness and practicality of switched television for both deaf-to-hearing and deaf-to-deaf communication. Proper attention is required, however, to terminal design and maintenance procedures. In the second part (Sections III and IV) consideration is given to extending the system to permit communication over the public switched telephone network. This demands considerable data compression of the images. Experiments are reported using six deaf subjects in which the tolerance of signing, lip-reading, and fingerspelling to temporal, spatial, and contrast coding distortions was investigated. The results suggest that just-comfortable communication can be achieved at around 100 kbits/s and just-possible communication at around 5 kbits/s, with further reductions appearing feasible.