Severely paralysed people can find it extremely distressing to lose the ability to communicate. While much work has already gone into developing eye-tracking systemsthese can be unreliable and tiring to use.
An alternative approach is to use electrodes implanted in the brainbut this is costly and carries an element of risk. More recentlyhoweverresearchers in the USA have developed a system that interprets the microvolt signals on the scalp that result from brain activity. And a team of design consultants has helped the researchers turn the bulkyexpensive research equipment into an affordable system suitable for use at home by paralysed people and their carers.
The novel brain-computer interface (BCI) translates brain waves into computer control commands by means of passive sensors placed on the scalp. Using such a system to operate a computer offers a genuine breakthrough in the way patients can communicate and perform their daily activities.
Initial work on the BCI system was carried out by the Wadsworth Centera public health laboratory for the New York State Department of Healthto help even individuals who are completely paralysed to communicate. Already the new BCI system has been shown to match the capabilities of costly invasive systems that require electrodes to be surgically implanted in the brain; it should therefore be able to help individuals who have lost all muscular controlwhich cannot be achieved by other augmentative or assistive communications approaches – such as eyeball-tracking systems.
Cambridge Consultantsa UK-based company with offices in the USAhelped the Wadsworth Center transform a complex set of research equipment into an affordableeasy-to usemore portable system that is suitable for the needs of patients and their carers.
“Our device requires neither implanted electrodes nor eye movement to help severely paralysed individuals to communicate” says Dr Jonathan Wolpawdirector of the BCI unit of the Wadsworth Center. “ We are trying to take a solution that might cost tens of thousands of dollars and make it work better at a price of around US$5000.”
The Wadsworth Center’s BCI system consists of three primary hardware components that operate in conjunction with specialised software. A mesh cap holds small sensor electrodes firmly against the user’s head. An amplifier is connected to the electrodes to convert the microvolt analogue signals received from the surface of the scalp into a more robust signalwhich is then translated into a digital signal and analysed by specially designed signal processing software running on a laptop PC.
Cambridge Consultants is helping Dr Wolpaw’s group transform its research-based system into a system suitable for daily use by non-scientists. One of the challenges was to develop a sensor cap that is comfortable enough for extended wearyet allows an untrained carer to position the sensors accurately on the user’s head. Positioning deviations from session to session of more than a few millimetres can dramatically affect the accuracy of the system. To minimise the affect of any positional changes‘smart’ software learns the accuracy of the response from the user and applies different weightings to the signals received from the sensors.
Early sensor cap designs were based on those used for EEG (electroencephalogram) recordingbut these use tension to ensure the sensors are held in close contact with the scalp. As suchthey are only suitable for wearing for up to two hourswhich is inadequate for the BCI application that calls for a cap that can be worn for 10hours or more.
Alternative cap designs were proposed that used concepts borrowed from surgeons’ caps (that might typically be equipped with lights and other devices) and sleep apnoea headgear that is worn all night. Several iterations of cap design were requiredas there was a fine balance to be struck between comfort and a snug fit. Finally the team established that the best material to use was a compressed open-cell foam that is the same as that used for footbeds in shoes.
A great deal of work has also gone into selecting the optimum amplifier to convert the microvolt signals into analogue signals for the PC. Whereas the Wadsworth Center had been utilising a 16-channel amplifier costing around US$8000Cambridge Consultants helped the Center to establish that an eight-channel amplifier would be adequate – at a cost of around US$4000.
A BCI system will only ever be as good as the user interfaceso Cambridge Consultants helped to simplify the research-driven interface. The result was a graphical software interface with icons and sound so that patients can more readily communicate with their carers; for examplepatients now can access icons for ‘water’ and ‘food’and traverse a menu with a variety of choices by using their brain waves to transcend the language barrier.
Patients make selections in either of two ways. In onethey pay attention to a particular icon displayed among many in a grid on the computer screen. As the various icons flash in successiona distinct electrical response is evoked in the brain by the attended icon. The system tracks the timing of the flashes and the evoked responseidentifies the attended icon and outputs the appropriate soundtextand/or environmental control signal. The system can also generate speech from those words created on the computerenabling users to communicate audibly with a carer if they choose.
In the second methodthe user can imagine particular movements. Even if the user is totally paralysedthis imagined action – such as moving a foot or curling the toes – generates a localised electrical stimulus in the brain that can be detected by the BCI system.
The system then maps that action to moving the computer cursor in a particular direction. In this mannerthe user can navigate menu structures to select actions and/or perform word processing activitiessimilar to the way in which people normally use a computer mouse.
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