Size and Distance Discrimination Using an Ultrasonic Aid for the Blind

Abstract

Blindfolded sighted observers made size and distance judgments based on information provided by the Kay Ultra aid for the blind. This aid feeds an audible tone to the user based on the difference between a frequency modulated ultrasonic beam and its returning echo. Distance judgments are, thus, based on pitch and size judgments on amplitude and scanning. Distance judgments were found to follow the traditional Weber's law and to be more precise than either visual perception or unaided echolocation. Size discrimination was also linearly related to stimulus magnitude and appears to be better than unaided echolocation but worse than vision. Changing the texture of the object upset both distance and size judgments. Changes in distance also upset size judgments, but changes in size did not upset distance judgments, indicating that distance judgments are more stable than size judgments.