Users of Hex-o-Spell are asked, for example, to move a finger of their right hand or a finger of their left hand. The brain signals in the sensorimotor cortex corresponding to the motor command for each movement occur in slightly different places. (Imagined movements can also be used, but since the technology is intended for users who may be amputees or paralyzed, the use of actual motor commands in the brain is better. In these patients, a ‘phantom command’ may be there but the movement is not.)
The 128 different channels of EEG data are filtered to help clarify the rhythms of interest and are then distilled down by a machine learning method known as common spatial patterns (CSP). This algorithm is trained on past data to produce filters that extract those values that vary the most for the regions of the brain likely to be most useful. Finally linear discriminant analysis (LDA) is used to distinguish the distilled values. This is a surprisingly old method, dating back to 1936, which seeks to group data into different classes by separating them with a line (or plane or hyperplane). To achieve this, the data is transformed (rotated) until the distance between data in the same class is minimised and between different classes is maximised. In this way, new EEG data can be classified as belonging to one or another class, and so the patterns corresponding to the intention to move the left or right finger can be identified.
which works out which letters are most likely to be chosen next, and places those closest to the arrow. This ensures that the user never has to rotate the arrow far to choose the next letter, and speeds up the whole process dramatically.
Hex-o-Spell was demonstrated at the CeBIT fair 2006 in Hannover with remarkable success. Two users who had little or no practise with any similar device successfully used the system for many hours. One person managed between 2.3 and 5 characters a minute and the other achieved between 4.6 and 7.6 characters a minute – world class performance for this type of BCI.
The Berlin BCI group is continuing its groundbreaking research. Collaborator Roderick Murray-Smith at Glasgow University explains the wider context of the work: “BCI vs general HCI can be compared to Formula 1 cars vs mass-production cars. BCI gives very extreme challenges to interaction designers, which at times force them to reconsider the basics of their field, because many standard techniques have implicit assumptions of fairly reliable input mechanisms. That means that techniques which prove their value in BCI might find application in a different form on, for example, mobile phones with novel sensors such as GPS & accelerometers.”
Once a signal has been identified by the computer, it is then fed into the Hex-o-Spell interface. This comprises six hexagons in a circle, each containing five symbols (letters of the alphabet, backspace and simple punctuation). If, say, the intention to move the right finger is detected, then an arrow in the middle will rotate, pointing to each hexagon in turn. If the intention to move the left finger is detected, then that arrow will grow in length until the current hexagon and its symbols are selected. Those symbols are then used to replace the contents of the six hexagons, and the arrow can once again be used to pick the single letter or punctuation required. The clever part in the system is the way the symbols are arranged – their presentation is automatically changed according to a predictive language model,
Work investigating how well patients can use the technology is underway now. If the wizards at the Berlin BCI group are successful, then one day anyone who can think, will be able to communicate, no matter what their physical disability might be.
Resources: Berlin Brain Computer Interfacing Project: http://ida.first.fhg.de/projects/bci/bbci_official/index_en.html PASCAL: http://www.pascal-network.org/ Challenge: http://ida.first.fhg.de/projects/bci/competition_iii/ Workshop: http://ida.first.fraunhofer.de/projects/ pascal_workshop/pascal_workshop.html Pump-priming project: http://www.dcs.gla.ac.uk/~jhw/dibci.htm