Project H: Play

Not everything has to be a paper. A two-player game where whoever relaxes harder wins, a visualizer that turns band power into colour, an instrument you play with your eyes closed: each one takes a weekend, teaches real-time signal processing under a deadline (the demo is at seven), and draws a crowd. The crowd is where clubs, collaborators, and occasionally employers come from.

Alpha tug-of-war

Two people, one channel each at O1, a rope on the screen. Every quarter second compute each player’s alpha power relative to their own two-minute baseline and move the rope toward the calmer player. Whoever relaxes harder wins. It is funny, it is instantly understood, and it quietly teaches normalization (why relative to baseline), latency (why the rope lags), and the fact that trying hard to relax does the opposite.

Sonification

Map delta, theta, alpha, and beta power to four notes’ loudness in a Web Audio or SuperCollider patch, or send them as MIDI to any synthesizer. Then map spectral shape to timbre. Then let an ERPEvent-related potential (ERP) The small, stereotyped voltage waveform the brain produces in response to an event, invisible in a single trial and revealed by averaging many. Related: P300P300 A positive bump about 300 milliseconds after a rare or meaningful stimulus, the basis of the classic BCI speller. , N170N170 A negative deflection about 170 milliseconds after seeing a face, over the back of the head on the right. , Error-related negativity (ERN)Error-related negativity (ERN) A sharp negative wave about 50 to 100 milliseconds after you make a mistake, before you consciously notice. , Trial averagingTrial averaging Adding many time-locked epochs together so the consistent response grows and the random noise shrinks by the square root of the number of trials. . Glossary entry trigger a drum. The listener’s ear picks out structure in 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 that the eye misses, and you learn that band power alone is a thin description of a signal.

Visuals and light

Band powers to the parameters of a generative shader, or to a strip of addressable LEDs, or to the brightness of the room. Slow and smooth reads as calm; fast and bright reads as busy. Perform it at a club meeting with the room’s lights driven by whoever is wearing the band.

A brain-controlled instrument

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, with the flickering targets mapped to notes or chords, so a musician plays with their gaze. Or 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 to switch patches, if you have trained enough. The 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 version works at the first rehearsal.

What to be careful about

All the usual: batteries, photosensitivity screening if anything flickers, consent from whoever puts the electrodesElectrode The conductor that turns ion currents in tissue into electron currents in a wire; its chemistry and contact quality set the noise you live with. Related: Silver/silver-chloride (Ag/AgCl)Silver/silver-chloride (Ag/AgCl) The standard electrode material for biopotentials, because its chemistry produces a stable, low-noise, low-drift interface with salty gel. , Electrode impedanceElectrode impedance How hard it is to push current through the skin-electrode contact, typically 5 to 50 kilohms with gel and megohms dry, higher at low frequencies. , Half-cell potentialHalf-cell potential The DC voltage that appears wherever a metal meets an electrolyte; two electrodes with different half-cell potentials produce an offset that can swamp the signal. . Glossary entry on. And a little honesty in the presentation. The rope is moving because of alpha power, which is a measure of visual cortex idling, not of “calm” in any deep sense. Say that. The demo is more interesting when it is true.