Troval is a hybrid Brain Computer Machine Interface (BCMI) artistic installation created by the biotronic artist Felix Vinyals and the EEG & BCI Researcher Oscar Portolés. Torval allows the musician to create music and control the lighting of the stage simultaneously with a Brain Computer Interface (BCI) device from Brain Products GmbH, Germany.
The installation is called hybrid because it combines two independent BCI systems. One system makes use of the Steady State Visual Evoked Potential (SSVEP) technique to allow the musician to switch on and off a set of music tracks from a MIDI sampler. The second system determines the musician’s index of relaxation that is read through the alpha rhythm to alter, accordingly, the illumination of the installation with a professional set of floodlights through DMX protocol.
Part of the installation has been assembled with an Arduino, specifically the MIDI and DMX controller due it does not need high computational power, the ease of coding and the enormous community that it have. Also the Arduino has the advantage that has been intended to easily prototype project that interact with the environment.
In Deep Description:
Torval consists of 6 main modules: the visual stimuli tool, the EEG signal acquisition unit, the signal processing algorithms for both BCI systems, the outputs control box (Bebop), the music sampler, and the illumination system.
On one hand, the visual stimuli tool elicits a SSVEP in the user visual cortex when he gazes at one of the six flickering stimuli. Then, the signal-processing algorithm searches the EEG data in real time for a SSVEP. When a SSVEP is found at a frequency coincident with one of the flickering stimulus units, the outputs control-box, Bebot, will send a MIDI command to switch on or off the musical loop associated with the particular flickering stimulus unit.
On the other hand, a signal-processing algorithm constantly monitors the level of relaxation of the artist – the power within the Alpha rhythm of the occipital cortex. Continuously and smoothly, Bebop modifies the illumination of the stage trough DMX protocol in correlation with the relaxation of the user; a shade from the colour spectrum that ranges from red to blue is projected onto the stage. Therefore, the user can actively control the colour of the stage. Yet, as he fully engages in the performance, he loses his ability to self-control his level of relaxation and mental load; turning the stage illumination into a genuine portrait of both physiological states.