Authors: Cindy Tonnesen and Gary Withrow

General Description

Biosensors are a neural interface technology that detect nerve and muscle activity. Currently, biosensors exist that measure muscle electrical activity, brain electrical activity, and eye movement. Biosensors are electrodes that sit on the skin over the muscle or nerve being sampled. Eye movement, for example, is determined from biosensors placed strategically on the forehead and under the eyes.

Electrical signals have many measurable qualities, including intensity and spectral characteristics. Energy is also measurable from a multitude of motor units. Just as the brain uses these signals to control functions of the human body, these signals can be detected by biosensors and then interpreted by software to control electronic devices external to the human body.


Biosensors have the potential to affect many areas. Field application areas including medicine, physical therapy, music, and the video game industry, can all benefit from the introduction of biosensors. Although biosensors are not limited to any group of people, they are particulary useful for the handicapped. Even completely paralyzed individuals have electrical activity in their bodies that can be detected.

One biosensor application developed for the handicapped is an electronic instrument that produces music from bioelectric signals [2]. Signal inputs such as eye movements, muscle tensions, and muscle relaxations are converted to MIDI (Musical Instrument Data Interface) and output to a synthesizer. Before being mapped to MIDI, the signals are analyzed for specific intensity and spectral characteristics for the particular individual. For dysfunctional or weak muscles the signals can be amplified according the the level of tension and relaxation. These signal inputs are then interpreted to control volume, pitch, tempo, and other aspects of musical composition.

Medical applications are presently seen in the diagnosis and correction of eye disorders [3]. Strabismus is a condition in which an individual's eyes are not aligned properly, and thus do not move in conjunction with one another. This can be corrected by surgery but the current use of prisms to determine the degree of correction necessary is not very accurate. Biosensors tracking the eye movements can determine with high accuracy the number of degrees in both the X and Y planes that the eyes need to be adjusted.

Just as biosensors can be used to determine amounts of eye correction, they can also be used to train the eye as they can be an input device to video game exercises to realign eye tracking. This same method of muscle training through a video game could be used for rehabilitation of potentially any muscle group, as biosensors can be individually customized to detect levels of muscle activity for most muscle groups. In the same way that patients undergoing rehabilitation could use biosensors as an input device for their video exercises, the video game industry could use biosensors as yet another powerful input device for entertainment.

Also contributing to physical therapy, biosensors can help to create custom exercise programs for injured patients and athletes, can be used by athletes to check muscle condition, and can be connected to a multitude of external monitoring devices.

Potential Uses in Virtual Reality

Biosensors potentially have a number of uses in the emerging field of Virtual Reality, particularly in the areas of user interaction and the development of these interaction devices.

Biosensors could be used as powerful input devices for immersive environments. Imagine a virtual environment in which your entire body was immersed. This environment could react to hand or arm gestures, eye movements, or any muscle or nerve as input. These forms of input are attractive as they are somewhat more natural and intuitive to the user, as the user is accustomed to manipulating the "real" world with such movements. These natural forms of input are successfully being researched with input devices such as gloves and body suits. Biosensors strategically placed on the body could provide an alternative way to provide this interface, and may be less encumbering than full body suits or gloves. They also could be utilized by handicapped people who may not be able to use a glove or body suit.

Currently, researchers are developing a biosensor wristband to detect electrical activity in the hand. Primitive gesture recognition has been successful, providing a possible alternative to a glove in the future [5].

Another possible, natural input to a virtual environment is muscle tension. This could be quite useful if utilized in the design of a glove. In this way input can be given to indicate if the user is touching or smashing an object in a virtual environment.

Eye movement also has important interaction implications in virtual reality. Wherever the user's eyes look, the virtual environment could be displayed appropriately. Furthermore, convergence of the eyes on a specific object in the environment could be detected. This could be used to select and object in the virtual environment. With the methods of head movement tracking currently used, the scene can be rendered, but it is difficult to tell if a specific object is being focused on by the user.

Biosensors could also be used to measure and analyze muscle activity and patterns, and in that way, aid in the development of VR hardware such as gloves, body suits, or robotic arms used in telepresence environments.

Future Goals

There are future applications that make biosensors ideal input devices. Eye tracking devices that can focus and select objects in 3D virtual environments would couple sight and limb 3D selection creating powerful immersive environments. The laser abilities from the eyes of 'Superman' could be realized by users in a virtual environment.

Possible use of prosthetic limbs where just the bioelectric activity to the nerve endings of a missing limb could be used to control an artificial limb. In cases of paralysis, the nerves, prior to loss of transport ability, or brainwaves might be electrically monitored for instructions to control/move a mechanical device attached to the paralyzed limb.

When brainwaves can be reliably monitored, we can study relationships between EEG (brain activity) and specific cognitive activities such as sleep behaviors and sleep states. Simple brain wave detection has been successful in early research stages, but breaking through the use of subvocal commands would be perhaps the most powerful input controller we have yet seen. Just picture monitoring brain activity so that when you think "draw a circle", a circle appears on your monitor or in your virtual environment.


[1]Lloyd, Anthony, Lusted, H.S., and Rick Rees, "Bio-Signal Processing: A New Platform," Biomuse Manual, Release 2, BioControl Systems Inc., 1992.

[2]R.B. Knapp and H.S. Lusted, "Musical Performance by the Handicapped Generated from Bioelectric Signals," presented at the 119th meeting of the Acoustical Society of America, Pennsylvania State University, May 22, 1990.

[3]R.B. Knapp and H.S. Lusted, "Biocontrollers for the Physically Disabled: A Direct Link from the Nervous System to Computer," Department of Electrical Engineering, San Jose State University and Stanford School of Medicine.

[4]R.B. Knapp and H.S. Lusted, "Biocontrollers: A Direct Link from the Nervous System to Computer," presented at the Medicine Meets Virtual Reality Conference, San Diego, CA, June 4-7, 1992.

[5]Lloyd, Anthony. BioControl Systems, Inc. Phone Conversation. October 7, 1993.

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Human Interface Technology Laboratory