Optimization of Man-Machine Interface for Real-Time Visual Information Transfer to the Visually Handicapped

Abstract

The research is directed at investigation of the parameters involved in optimization of the man-machine interface for transmission, recognition and individual control of real-time visual information access for the visually handicapped. Three overlapping areas are considered -- the visual information access with the concept of controlled feedback for distance, depth of field, focus and angle of observation; the basic parameters of physiological neural integration combined with the electro-mechanical interface of vibrator-matrix-to-skin information exchange and recognition; and the detail of micro miniature circuit design to provide the optimum signal processing and transducer excitation. The theoretical solutions are implemented in a prototype capability used experimentally to validate the system operation and to identify critical parameter values.The boundary values of non-invassive acceptance, neural X-Y correlation and recognition, and skin sensitivity versus pain thresholds resulted in the selection of a vibrotactile array as the man-machine interface, each of the miniature vibrators being individually driven at four levels of excitation with controlled presentation parameters of random, sweep, and trace, and with possible selection of mode by the operator. The paper presents the theory and experimental results of threshold and recognition sensitivity versus the control parameters of pulse shape, repetition frequency, duty cycle, pulses per burst, and recovery period for skin adaptation versus driving power and noise level.The visual information access was optimized using a light-sensitive RAM with a 128x256 matrix array, reduced to fit the tactile unit, coupled to a focusing lens with eventual capability to control depth of focus and visual field angle. Signal processing and vibrator drive requirements involve the theoretical design and optimization of microprocessor circuits capable of providing the necessary control of the critical parameters of wave shape, randomization of vibrator excitation, sweep, trace, or random presentation together with four levels of amplitude representing four gray levels of light. Vibrator noise is reduced to 70dBC or less by special excitation pulse wave shaping and storing of the pulse in memory.The paper presents details of the three system areas, their experimental validation on both sighted and blind subjects, with possible feedback optimization capabilities available to the operator.