Robot sensing Museum visitors could interact with four robot sensing modalities: vision, hearing, touch, and sonar. Vision: after arranging a set of simple shapes on a board, a vision system attempted to recognize them using edge detection. Hearing: this was exemplified by a speech recognition system. Touch: visitors touch a pressure-sensitive pad that outputs the distribution of pressure under their figures onto a display. Sonar: a ceiling-mounted sensor measured a visitor's height by bouncing a signal off the top of the head.