A non-invasive device that allows severely paralysed people to interact with a computer via their brain signals has been improved to make it a viable commercial product by Cambridge Consultants (CCL).
Known as a brain-computer interface (BCI), the device uses electroencephalography (EEG) to detect microvolt brain signals, then applies an adaptive algorithm that focuses on the EEG features the person is best able to control.
Those signals can be mapped onto functions for tasks such as manoeuvring a cursor around a PC screen, or for spelling out words for a speech synthesiser.
The system, developed by researchers at the Wadsworth Center, a New York State health unit, originally used a large, $13,000 64-channel amp and the user had to wear a bulky cap to apply 64 electrodes to the skull.
CCL’s input involved reducing the size, complexity and cost to make it more suitable for home or hospital use.
CCL also modified the on-screen menu system through which brain signals are acquired, and added a synthetic voice – a requirement if potential users were to claim financial assistance from US medical insurance organisations.
“The sensor cap was designed to be worn for an hour or two at a time,” said Mark Manasas, manager for surgical and interventional devices in CCL’s Boston office. “We looked at it from the point of view of a user wearing it for most of the day, and reduced the number of sensors from 64 to eight.”
Accuracy was maintained through improvements in the spatial mapping and signal processing of the EEG.
“In the future we’d love to get to active electrodes on the cap, which amplify the signal right at the scalp, but for weight reasons and medical regulations the first step is just to reduce the number of sensors and keep them passive.”
The cost of the enhanced system has been reduced to $5,000, the amount users can claim from Medicare for a speech-assist device.
Stimulating spikes in brain activity
Systems for brain-computer interaction use two different approaches, the so-called p300 response, and sensory motor rhythms (SMR). The p300 technique elicits a microvolt spike in brain activity, which has a particular waveform, by using a ‘surprise’ visual, audio or tactile stimulus.
In this case the system displays a grid of symbols on the PC screen and the user concentrates on the letters of the word they want to spell out. “The key is, there is a delay of about 300ms from the time the response happens on the screen to the time of the brain spike,” says CCL’s Mark Manasas.
“As the screen flashes a matrix of items, a user focuses on one of the cells in the matrix. If you want to spell the word ‘BOY’ you might have a matrix of letters on the screen and as the B flashes the brain spikes.”
The computer would then look back at what flashed on the screen 300ms before the spike and associate it with the letter B.
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