Abstract
Discusses the development of electronic travel aids for the blind, considering in particular the use of IF and US devices. Problems associated with focusing, resolution and ranging are discussed and three methods of modulation are considered-pulse modulation, pulse repetition modulation and frequency modulation. Methods used for information processing and display are also discussed. As examples, the Sonic Guide (an FM ultrasonic aid) and the Sonic Pathfinder (a prototype pulse echo ultrasonic aid) are described