Project B: Control for a real user
EMG or EEG control of a wheelchair, a robot arm, or a drone, for a specific person. Drone-by-brain is a demo. Wheelchair-by-muscle for someone who cannot use a joystick is a life.
On this pageA semester
The eight-channel armband recognized your gestures. The motor imageryMotor imagery Imagining a movement without making it, which changes rhythms over motor cortex in a way a classifier can sometimes detect. Related: Sensorimotor rhythm (mu)Sensorimotor rhythm (mu) An 8 to 13 Hz rhythm over motor cortex that weakens when you move, or imagine moving, the corresponding body part. , Event-related desynchronization (ERD)Event-related desynchronization (ERD) The drop in rhythmic power over a cortical area when it becomes active, such as mu weakening when you imagine moving your hand. , BCI inefficiencyBCI inefficiency The finding that around one in five people cannot control a motor-imagery BCI even after training; once called "BCI illiteracy," a label the field is retiring. . Glossary entry classifierClassifier An algorithm that assigns each trial a label, such as left hand or right hand, after being trained on labelled examples. Related: Linear discriminant analysis (LDA)Linear discriminant analysis (LDA) A simple, robust classifier that draws a straight boundary between classes; the workhorse of EEG decoding for two decades. , Support vector machine (SVM)Support vector machine (SVM) A classifier that finds the boundary with the widest margin between classes; strong on small datasets. , Cross-validationCross-validation Testing a model on data it never saw during training, repeatedly, so the reported accuracy means something. . Glossary entry moved a bar, sometimes. Now the question is who could use either. A person with a high spinal cord injury who cannot grip a joystick may have shoulder or neck EMGElectromyography (EMG) Recording the electrical activity of muscles, hundreds of microvolts to millivolts, much larger than EEG. Related: Myoelectric prosthesisMyoelectric prosthesis An artificial limb controlled by EMG from the remaining muscles. , Electroencephalography (EEG)Electroencephalography (EEG) Recording the brain's electrical activity from electrodes on the scalp, a few tens of microvolts of blurred, summed cortical activity. . Glossary entry. A person with cerebral palsy may have reliable EMGElectromyography (EMG) Recording the electrical activity of muscles, hundreds of microvolts to millivolts, much larger than EEG. Related: Myoelectric prosthesisMyoelectric prosthesis An artificial limb controlled by EMG from the remaining muscles. , Electroencephalography (EEG)Electroencephalography (EEG) Recording the brain's electrical activity from electrodes on the scalp, a few tens of microvolts of blurred, summed cortical activity. . Glossary entry at one site and unreliable movement everywhere else. Find the person, find the signal they have, and build the controller for it. The result will be less flashy than a drone and will change how someone gets across a room.
A person with a C4 spinal cord injury cannot move their arms or hands. Which control signal is most likely available and reliable?
EMGElectromyography (EMG) Recording the electrical activity of muscles, hundreds of microvolts to millivolts, much larger than EEG. Related: Myoelectric prosthesisMyoelectric prosthesis An artificial limb controlled by EMG from the remaining muscles. , Electroencephalography (EEG)Electroencephalography (EEG) Recording the brain's electrical activity from electrodes on the scalp, a few tens of microvolts of blurred, summed cortical activity. . Glossary entry from muscles above the injury: the sternocleidomastoid and trapezius in the neck and shoulder, or facial muscles, plus head movement. These are large, reliable, learnable signals, which is why commercial wheelchair controls for high injuries use head arrays and chin joysticks. Motor imageryMotor imagery Imagining a movement without making it, which changes rhythms over motor cortex in a way a classifier can sometimes detect. Related: Sensorimotor rhythm (mu)Sensorimotor rhythm (mu) An 8 to 13 Hz rhythm over motor cortex that weakens when you move, or imagine moving, the corresponding body part. , Event-related desynchronization (ERD)Event-related desynchronization (ERD) The drop in rhythmic power over a cortical area when it becomes active, such as mu weakening when you imagine moving your hand. , BCI inefficiencyBCI inefficiency The finding that around one in five people cannot control a motor-imagery BCI even after training; once called "BCI illiteracy," a label the field is retiring. . Glossary entry EEGElectroencephalography (EEG) Recording the brain's electrical activity from electrodes on the scalp, a few tens of microvolts of blurred, summed cortical activity. Related: Electrocorticography (ECoG)Electrocorticography (ECoG) Recording from electrodes placed on the surface of the brain under the skull, usually during epilepsy surgery evaluation; cleaner and sharper than EEG. , Magnetoencephalography (MEG)Magnetoencephalography (MEG) Recording the tiny magnetic fields produced by cortical currents with superconducting sensors in a shielded room; less blurred by the skull than EEG, and far more expensive. , Volume conductionVolume conduction The spreading of currents from a source through the conductive tissues of the head, which is why one source shows up on many electrodes and why scalp EEG is blurry. , Microvolt (µV)Microvolt (µV) One millionth of a volt. Scalp EEG is tens of microvolts; a AA battery is 1.5 million of them. . Glossary entry is the last resort, not the first, because its reliability is a fraction of EMGElectromyography (EMG) Recording the electrical activity of muscles, hundreds of microvolts to millivolts, much larger than EEG. Related: Myoelectric prosthesisMyoelectric prosthesis An artificial limb controlled by EMG from the remaining muscles. , Electroencephalography (EEG)Electroencephalography (EEG) Recording the brain's electrical activity from electrodes on the scalp, a few tens of microvolts of blurred, summed cortical activity. . Glossary entry’s. Building the reliable thing first is what the person needs; the EEGElectroencephalography (EEG) Recording the brain's electrical activity from electrodes on the scalp, a few tens of microvolts of blurred, summed cortical activity. Related: Electrocorticography (ECoG)Electrocorticography (ECoG) Recording from electrodes placed on the surface of the brain under the skull, usually during epilepsy surgery evaluation; cleaner and sharper than EEG. , Magnetoencephalography (MEG)Magnetoencephalography (MEG) Recording the tiny magnetic fields produced by cortical currents with superconducting sensors in a shielded room; less blurred by the skull than EEG, and far more expensive. , Volume conductionVolume conduction The spreading of currents from a source through the conductive tissues of the head, which is why one source shows up on many electrodes and why scalp EEG is blurry. , Microvolt (µV)Microvolt (µV) One millionth of a volt. Scalp EEG is tens of microvolts; a AA battery is 1.5 million of them. . Glossary entry version is research.
Find the person and the signal
Through the rehabilitation hospital’s occupational therapists, an independent living centre, or the Utah Assistive Technology Program. The occupational therapist knows what controls have been tried and why they failed. Map the person’s reliable voluntary signals: which muscles they can contract on command, how repeatably, for how long before fatigue. Record each candidate site with the armband hardware. The signal with the highest repeatable signal-to-noise and the least fatigue wins, whatever it is.
The controller
Two to four discrete commands is the realistic starting point: forward, stop, left, right; or open, close, and a mode switch. Map them to gestures the person can make reliably: a short contraction, a long one, two in a row. Add a confirmation for anything dangerous. Give continuous visual and auditory feedback of what the system thinks it saw, so the person can correct. Latency under 300 ms.
For a wheelchair, do not drive the motors yourself. Commercial chairs accept alternative input devices through a standard interface; your controller emulates a switch array or a joystick voltage through that interface, inheriting the chair’s own safety systems. For a robot arm, the same: command a well-tested arm’s API, do not build the arm.
Iterate with the person
Session one: the person uses it for ten minutes in a safe space while you watch. What confused them, what fatigued them, what did the system get wrong. Session two: the fixed version. Repeat weekly. Measure the things that matter to them: time to cross the room, number of unintended stops, how long they can use it before tiring. Then measure the things the FMEAFMEA Failure mode and effects analysis: a table of every way the device could fail, how bad and how likely each is, and what you did about it. Related: ISO 14971ISO 14971 The international standard for medical device risk management that every company follows. . Glossary entry cares about: false activations per hour.
The EEG version
If the person has no reliable EMGElectromyography (EMG) Recording the electrical activity of muscles, hundreds of microvolts to millivolts, much larger than EEG. Related: Myoelectric prosthesisMyoelectric prosthesis An artificial limb controlled by EMG from the remaining muscles. , Electroencephalography (EEG)Electroencephalography (EEG) Recording the brain's electrical activity from electrodes on the scalp, a few tens of microvolts of blurred, summed cortical activity. . Glossary entry, or if they and you want to try, add motor imageryMotor imagery Imagining a movement without making it, which changes rhythms over motor cortex in a way a classifier can sometimes detect. Related: Sensorimotor rhythm (mu)Sensorimotor rhythm (mu) An 8 to 13 Hz rhythm over motor cortex that weakens when you move, or imagine moving, the corresponding body part. , Event-related desynchronization (ERD)Event-related desynchronization (ERD) The drop in rhythmic power over a cortical area when it becomes active, such as mu weakening when you imagine moving your hand. , BCI inefficiencyBCI inefficiency The finding that around one in five people cannot control a motor-imagery BCI even after training; once called "BCI illiteracy," a label the field is retiring. . Glossary entry or SSVEPSteady-state visual evoked potential (SSVEP) When you stare at something flickering at a fixed rate, visual cortex oscillates at that rate, and the frequency can be read straight out of the EEG spectrum. Related: Canonical correlation analysis (CCA)Canonical correlation analysis (CCA) Finding the combination of channels that correlates best with reference sinusoids at each candidate frequency; the standard SSVEP decoder. , Brain-computer interface (BCI)Brain-computer interface (BCI) A system that turns measured brain activity into control of something outside the body, from a cursor to a wheelchair to a speech synthesizer. . Glossary entry as a command channel. Report its accuracy next to the EMGElectromyography (EMG) Recording the electrical activity of muscles, hundreds of microvolts to millivolts, much larger than EEG. Related: Myoelectric prosthesisMyoelectric prosthesis An artificial limb controlled by EMG from the remaining muscles. , Electroencephalography (EEG)Electroencephalography (EEG) Recording the brain's electrical activity from electrodes on the scalp, a few tens of microvolts of blurred, summed cortical activity. . Glossary entry’s, honestly. Most of the time EMGElectromyography (EMG) Recording the electrical activity of muscles, hundreds of microvolts to millivolts, much larger than EEG. Related: Myoelectric prosthesisMyoelectric prosthesis An artificial limb controlled by EMG from the remaining muscles. , Electroencephalography (EEG)Electroencephalography (EEG) Recording the brain's electrical activity from electrodes on the scalp, a few tens of microvolts of blurred, summed cortical activity. . Glossary entry wins by a wide margin. Knowing that, from your own measurements on a real person, is worth more than a drone video.
- Find the person through an occupational therapist. Get onto the protocol. Listen, twice.
- Map their reliable signals with the armband hardware. Pick one or two sites.
- Build a two-command controller with feedback and a kill switch. Test it on yourself, then on a simulator on screen.
- Write the FMEAFMEA Failure mode and effects analysis: a table of every way the device could fail, how bad and how likely each is, and what you did about it. Related: ISO 14971ISO 14971 The international standard for medical device risk management that every company follows. . Glossary entry. Have the therapist read it.
- First live session in a safe space with the chair or arm limited. Iterate weekly.
- Measure task time, unintended activations, and fatigue over four sessions. Report.
- Hand over with a setup guide the caregiver can follow, and a support plan.