Investigations into a complex optical mobility aid for the blind

Retallack, Lawrence James (1976) Investigations into a complex optical mobility aid for the blind. University of Southampton, Doctoral Thesis.

Abstract

An examination of existing mobility aids for the blind reveals that most have a very limited operating range, and that none are adaptable in the sense of providing a variable amount of information dependent upon the situation and the time available for information assimilation. It is argued that the capability of supplementing short range-simple message information essential for obstacle avoidance with more detailed descriptions of any part of the visible environment could improve the mobility of blind travellers and enable them to obtain a greater appreciation of their environment.The implication is a device operating fully automatically in mobility situations, but with a large input data base and user override of the automatic operation when slower, more detailed examination of the environment is desired.A television camera is used as the input sensor for a prototype device. The three most important automatic functions are focusing and range finding, exposure control, and selection of the important area of the image plane. Concentration is highest on the first function as depth perception was originally expected to be the limiting factor on service performance. By examining spatial frequency content of the camera image, focusing is performed by maximising the high frequency image modulation; range information is obtained by lens focusing ring position when focus has been attained. Based on computer analysis of image spectra, a two-fold optimising controller is developed which maximises the signal to noise ratio for focusing on a single object, simultaneously allowing for the effect of other objects on the spectrum of the first in a multiple obj%act situation. Controller performance is concluded to be adequate for the mobility aid providing that good quality cameras are available and that operating speed can be increased.The exposure controller operates on the average light level across the entire image plane, although modifications required for operation on a selected area are described. Possible automatic area selection circuits are discussed based on experience with the camera and with implemented manual selection circuits.For encoding visual information for the blind, tactile and auditory inputs are considered with preference given to the latter for complex displays. Experiments are described which establish natural correlations between sound characteristics and sound source locations. Using results of these studies and work performed elsewhere, a possible encoding scheme is presented.In conclusion, the practicability of some aspects of the originally proposed mobility aid are indicated, and it is suggested that a second prototype is both worthwhile and necessary to prove the usefulness of the complex passive optical device as a help to blind mobility.

This record has no associated files available for download.

Contributors

Download statistics