Wired Muscle

Wired Muscle: Generating Faster Kinesthetic Reaction by Inter-personally Connecting Muscles

Jun Nishida, Shunichi Kasahara, and Kenji Suzuki
ACM SIGGRAPH 2017 Emerging Technologies

The collaboration project with Jun Nishida and Kenji Suzuki (University of Tsukuba).

Paper (ACM Digital Library)

Abstract

Instantaneously generating own body movements in response to the movement of others, such as establishing defensive posture in sports and learning kick-out timing from therapists in gait rehabilitation, is an essential aspect of interpersonal exercises and contact sports. However, ignition of movement based on a visual stimulus requires approximately 250 milliseconds (ms), which is too late for certain interpersonal physical interactions that require immediate reaction. Thus, we introduce “Wired Muscle,” a system that connects muscle activities between two persons using electromyogram (EMG) measurement and electrical muscle stimulation (EMS) to generate responsive movement that are faster than those generated by the visual information-based process. Our system detects the muscle activity of a person by the EMG and triggers the EMS to drive the muscle of the other person to induce corresponding counter movements. In a pilot study using our system, the reaction time to the motion of another person could be shortened to approximately 60 ms. In addition, some participants perceive that the kinesthetic reaction was performed by their own will even though the muscle movement was electrically driven by prior stimuli. We envision that our system will enable direct connection of kinesthetic experiences among multiple persons and will form the basis for a novel paradigm of motor learning.

Reacting faster than sight allows

In contact sports and in rehabilitation, people have to respond to another person’s movements with their own body, for example by taking a defensive posture against an opponent or by learning from a therapist when to kick out the leg while walking. A reaction to what we see takes about 250 ms: the time to register the other person’s movement, recognize the situation and send a command to the muscles. For some physical interactions this is too slow.

Wired Muscle connects the muscles of two people directly. Each person wears a bioSync device, a wearable kinesthetic input and output device whose electrodes measure muscle activity with electromyography (EMG) and stimulate muscles with electrical muscle stimulation (EMS) at the same time. On person A, the device detects the muscle activity of a movement; when the signal exceeds a threshold, the device on person B immediately stimulates the muscle that produces the corresponding counter movement. EMG picks up muscle activity even when the movement is hard to see, so the trigger can come much earlier than a reaction to sight. And because the EMS moves B’s own muscle, B feels the movement through their own kinesthetic and tactile senses.

A faster reaction that feels like one’s own

Wired Muscle let the second person grab a falling bar 60 ms after the first person released it, far sooner than a reaction to sight, and some participants felt that they had made this electrically driven grab by their own will.

We demonstrated this with a bar drop test, a common way to measure reaction time to a visual stimulus. Person A opened their hand to release a bar, and person B tried to grab it without looking at their hands. The device on A detected the muscle activity of the extensor that opens the hand, and the device on B stimulated the flexor that closes B’s hand. Detecting the release and driving the EMS took about 10 ms, and the stimulated muscle took about 50 ms to contract. A voluntary grab takes about 250 ms in response to sight and about 170 ms in response to a kinesthetic stimulus, depending on the person’s expertise.

B’s own muscle activity shows what happens next: B’s voluntary grab started about 110 ms after the involuntary one, prompted by the kinesthetic and tactile sensation of the stimulated movement. The two movements go in the same direction and follow each other closely. Our empirical studies indicate that this spatial and temporal consistency lets the two be interpreted as a single, faster voluntary movement: the rapid reaction to another person’s movement can be perceived as a “virtual” voluntary action, one that people feel they performed themselves (a sense of agency), although a computer drove it.

Learning reactions through one’s own body

EMS has been used to move people’s muscles so that they learn a movement, for example to play a musical instrument by reproducing recorded motions. Contact sports instead require immediate reactions to an opponent’s many unexpected movements. If the correspondence between one person’s muscle activity and the appropriate response of another is recorded beforehand, Wired Muscle could generate such reactive movements, and a martial arts student could learn by experiencing their own successful responses, in time, through their own kinesthetic sense. The current system drives a single movement; multiple channels could extend it to reactions involving more complex muscle activity, and sharing each other’s views, as in Parallel Eyes, could make the connected experience spatially consistent and lower the cognitive load of learning.

Reference

Jun Nishida, Shunichi Kasahara, and Kenji Suzuki. 2017. Wired Muscle: Generating Faster Kinesthetic Reaction by Inter-personally Connecting Muscles. In ACM SIGGRAPH 2017 Emerging Technologies (SIGGRAPH ’17). Association for Computing Machinery, New York, NY, USA, Article 26, 1–2. https://doi.org/10.1145/3084822.3084844

@inproceedings{10.1145/3084822.3084844,
  author    = {Nishida, Jun and Kasahara, Shunichi and Suzuki, Kenji},
  title     = {Wired Muscle: Generating Faster Kinesthetic Reaction by Inter-personally Connecting Muscles},
  booktitle = {ACM SIGGRAPH 2017 Emerging Technologies},
  series    = {SIGGRAPH '17},
  year      = {2017},
  articleno = {26},
  pages     = {1--2},
  publisher = {Association for Computing Machinery},
  address   = {New York, NY, USA},
  doi       = {10.1145/3084822.3084844}
}

Figures from the paper (Nishida et al., SIGGRAPH ’17 Emerging Technologies). © 2017 Copyright held by the owner/author(s).

• News: Wired Muscle on Japanese TV News
• Related projects: Preemptive Action (measures how early EMS can move the body while preserving the sense of agency, and suggests a retuned timing for Wired Muscle), EMS Speeds Up, Faster Than Muscle