A collaboration between researchers in Australia, Japan and the U.S. has resulted in a device which can remotely control a person’s movements by stimulating the vestibular system, an inner ear structure which controls balance, movement and orientation in space.
The vestibular system (also called the ‘labyrinth’) consists of three fluid-filled semi-circular canals, arranged orthogonally so that each is in a different plane. The semi-circular canals sense the rotation of the head, and feed back to the neural circuitry controlling eye movements produces the vestibular-ocular reflex, which adjusts eye movements so that the visual field remains steady and images remain in focus; feedback to the motor system maintains an upright posture.
Other components of the vestibular system include the otoliths (the utricle and saccule), which are located between the semi-circular canals and the cochlea. These structures are composed of calcium carbonate crystals and a gelatinous matrix, and sense gravity and linear acceleration which occur due to movements in a straight line.
Researchers from the Nippon Telegraph and Telephone Communication Science Laboratories in Japan demonstrated a similar device at SIGGRAPH2005, the 32nd International Conference on Computer Graphics and Interactive Techniques, in Los Angeles.
This prototypical device induced a virtual sense of acceleration, and consisted of a set of headphones and a remote control which could deliver electrical charges to the vestibular system of volunteers, who swayed from side to side in response. Volunteers had to wear a blindfold, so that the brain did not use visual stimuli to adjust movement.
Stephen Moore, an associate professor of neurology at Mount Sinai School of Medicine, studies how the vestibular system controls posture and gaze, and is currently trying to develop better flight simulators for astronauts.
In the film clip below, Moore walks using the device, which can be seen in place over his left ear. Halfway through the clip, the remote control is used to electrically stimulate his vestibular system, causing him to sway first to one side and then to the other.
“It makes you feel like you’re moving in a certain direction, but it’s not really that specific. That’s the big limiting factor,” says Moore.
The Australian researchers involved in the research have developed a method for overcoming this problem. For unknown reasons, volunteers were ‘steered’ more accurately when they looked up to the sky or down at the ground.
According to Moore, the newer device is “not very practical” because of the “lack of specificity” of the electrical input, and because electrical stimulation of the vestibular system is still “overridden by visual input”.
In one of his books, the neurologist Oliver Sacks describes a patient who sustained inner ear damage as a result of a meningitis infection. Consequently, the patient walked with his body bent sideways at an angle of almost 45 degrees. After racking his brains, Sacks finally gave the man a pair of glasses that had a horizontal bar attached to them. When he wore the glasses, the patient could use the bar to correct his posture by adjusting it in relation to horizontal objects in his environment.
Devices which stimulate the vestibular nerve may be used to treat people with similar vestibular system disorders. To achieve this, Daniel Merfeld of the Massachusetts Eye and Ear Infirmary, is working to develop vestibular system-stimulating device which works like a cochlear implant. Similar devices may also be integrated into prosthetics for use by people with balance disorders.
- Fitzpatrick, et al (2006). Resolving head rotation for human bipedalism. Curr. Biol. 16: 1509-1514 (Abstract).