Scientists are developing a new space boot that can prevent astronauts or visually impaired people from tripping by using vibrations to guide the wearer around and over obstacles. Most falls happen because spacesuits limit astronauts' ability to both see and feel the terrain around them, researchers said. The space boot being developed by researchers from Massachusetts Institute of Technology (MIT) and Charles Stark Draper Laboratory in the US has built-in sensors and tiny "haptic" motors, whose vibrations can guide the wearer around obstacles. In a preliminary study, researchers determined what types of stimuli, administered to what parts of the foot, could provide the best navigation cues. On the basis of that study, they are planning trials using a prototype of the boot. The work could also have applications in the design of navigation systems for the visually impaired. The development of such systems has been hampered by a lack of efficient and reliable means of communicating spatial information to users. Researchers developed a device that spaced six haptic motors around each of a subject's feet - one motor each at the heel, big toe, and instep, and three motors along the outer edge of the foot. The intensity of the motors' vibrations could be varied continuously between minimum and maximum settings. In the study, subjects placed their feet in the device while seated before a computer. Software asked the subjects to indicate when they felt vibrations and at what locations on the foot. The researchers had envisioned that variations in the intensity of the motors' vibrations could indicate distance to obstacles, as measured by sensors built into the boot. However, they found subjects had difficulty identifying steady changes in intensity. They also had difficulty distinguishing between the locations of stimuli on the outer edge of the foot. On the basis of the study results, researchers are developing a boot with motors at only three locations: at the toe, at the heel, and toward the front of the outside of the foot - away from the middle location where stimuli sometimes did not register. The motor at the side of the foot could help guide the user around obstacles, but the first trial of the boot will concentrate entirely on the problem of stepping over obstacles of different heights. The researchers will also be evaluating the haptic signals in conjunction with, and separately from, visual signals, to determine the optimal method of conveying spatial information. "This work could be useful not only for astronauts but for firemen, who have well-documented issues interacting with their environment, and for people with compromised sensory systems, such as older adults and people with disease and disorders," said Shirley Rietdyk, at Purdue University.