Massively parallel signal processing using the graphics processing unit for real-time brain–computer interface feature extraction

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Wilson JA, Williams JC

Abstract: The clock speeds of modern computer processors have nearly plateaued in the past 5 years. Consequently, neural prosthetic systems that rely on processing large quantities of data in a short period of time face a bottleneck, in that it may not be possible to process all of the data recorded from an electrode array with high channel counts and bandwidth, such as electrocorticographic grids or other implantable systems. Therefore, in this study a method of using the processing capabilities of a graphics card [graphics processing unit (GPU)] was developed for real-time neural signal processing of a brain–computer interface (BCI). The NVIDIA CUDA system was used to offl oad processing to the GPU, which is capable of running many operations in parallel, potentially greatly increasing the speed of existing algorithms. The BCI system records many channels of data, which are processed and translated into a control signal, such as the movement of a computer cursor. This signal processing chain involves computing a matrix-matrix multiplication (i.e., a spatial filter), followed by calculating the power spectral density on every channel using an auto-regressive method, and finally classifying appropriate features for control. In this study, the first two computationally intensive steps were implemented on the GPU, and the speed was compared to both the current implementation and a central processing unit-based implementation that uses multi-threading. Significant performance gains were obtained with GPU processing: the current implementation processed 1000 channels of 250 ms in 933 ms, while the new GPU method took only 27 ms, an improvement of nearly 35 times.

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Dasher Speller

Here is a video of a person using the Dasher spelling system with EEG control. This uses a slightly different method of selecting the letters, in which the person imagines moving different body parts to make the cursor move up and down. For example, imagining both hands makes the cursor move up, and both feet make it go down.

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Brain-Twitter Interface Story on Wisconsin Public Radio

Audio from our interview with Shamane Mills, from Wisconsin Public Radio.

wpr-shamane-mills4202009

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Brain-Twitter Interface

In early April, Adam Wilson posted a status update on the social networking website Twitter—just by thinking about it.

Just 23 characters long, his message, “using EEG to send tweet,” demonstrates a natural, manageable way in which “locked-in” patients can couple brain-computer interface technologies with modern communication tools.

A University of Wisconsin-Madison biomedical engineering doctoral student, Wilson is among a growing group of researchers worldwide who aim to perfect a communication system for users whose bodies do not work, but whose brains function normally. Among those are people who have ALS, brain-stem stroke or high spinal cord injury.

Some brain-computer interface systems employ an electrode-studded cap wired to a computer. The electrodes detect electrical signals in the brain—essentially, thoughts—and translate them into physical actions, such as a cursor motion on a computer screen. “We started thinking that moving a cursor on a screen is a good scientific exercise,” says Justin Williams, a UW-Madison assistant professor of biomedical engineering and Wilson’s advisor. “But when we talk to people who have locked-in syndrome or a spinal cord injury, their No. 1 concern is communication.”

In collaboration with Research Scientist Gerwin Schalk and colleagues at the Wadsworth Center in Albany, New York, Williams and Wilson began developing a simple, elegant communication interface based on brain activity related to changes in an object on screen.

The interface consists, essentially, of a keyboard displayed on a computer screen. “The way this works is that all the letters come up, and each one of them flashes individually,” says Williams. “And what your brain does is, if you’re looking at the ‘R’ on the screen and all the other letters are flashing, nothing happens. But when the ‘R’ flashes, your brain says, ‘Hey, wait a minute. Something’s different about what I was just paying attention to.’ And you see a momentary change in brain activity.”

Wilson, who used the interface to post the Twitter update, likens it to texting on a cell phone. “You might have to press a button four times to get the character you want,” he says of texting. “So, this can be a slow process at first.”

However, as with texting, users improve as they practice using the interface. “People are able to do up to ten characters per minute,” says Wilson.

A free service, Twitter has been called a “micro-blogging” tool. User updates, called tweets, have a 140-character limit—a manageable message length that fits locked-in users’ capabilities, says Williams.

Tweets are displayed on the user’s profile page and delivered to other Twitter users who have signed up to receive them. “So, someone could simply tell family and friends how they’re feeling today,” says Williams. “People at the other end can be following their thread and never know that the person is disabled. That would really be an enabling type of communication means for those people—and I think it would make them feel, in the online world, that they’re not that much different from everybody else.”

Schalk agrees. “This is one of the first—and perhaps most useful—integrations of brain-computer interface techniques with Internet technologies to date,” he says.

While widespread implementation of brain-computer interface technologies are still years down the road, Wadsworth Center researchers, as well as those at the University of Tübingen in Germany, are starting in-home trials of the equipment. Wilson, who will finish his PhD soon and begin postdoctoral research at Wadsworth, plans to include Twitter in the trials.

Williams hopes the Twitter application is the nudge researchers need to refine development of the in-home technology. “A lot of the things that we’ve been doing are more scientific exercises,” he says. “This is one of the first examples where we’ve found something that would be immediately useful to a much larger community of people with neurological deficits.”

Funding for the research comes from the National Institutes of Health, the UW-Madison Institute for Clincial and Translational Research, the UW-Madison W.H. Coulter Translational Research Partnership in Biomedical Engineering, the TRACE Center at the University of Wisconsin, and the Wisconsin Alumni Research Foundation.

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Positioning and guidance of neurons on gold surfaces by directed assembly of proteins using Atomic Force Microscopy

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Staii C, Viesselmann C, Ballweg J, Shi L, Liu GY, Williams JC, Dent EW, Coppersmith SN, Eriksson MA.

Abstract: We demonstrate that Atomic Force Microscopy nanolithography can be used to control effectively the adhesion, growth and interconnectivity of cortical neurons on Au surfaces. We demonstrate immobilization of neurons at well-defined locations on Au surfaces using two different types of patterned proteins: 1) poly-d-lysine (PDL), a positively charged polypeptide used extensively in tissue culture and 2) laminin, a component of the extracellular matrix. Our results show that both PDL and laminin patterns can be used to confine neuronal cells and to control their growth and interconnectivity on Au surfaces, a significant step towards the engineering of artificial neuronal assemblies with well-controlled neuron position and connections.

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MIT Technology Review

Two NITRO areas of research were recently featured on the MIT Technology Review website, seen here:

Less-Invasive Brain Interfaces
Tongue Control

The original posters that these articles are based on can be found in the Publications section of our website.

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2-Dimensional Electrotactile Feedback for a BCI Using a Tongue Display System for Sensory-Substitution

Wilson NIC 2008 Poster

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Electrotactile Vision Substitution Matches Vision-Only Performance in a Brain-Computer Interface Task

Wilson SfN 2008 Poster

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Algorithm survey

Birch2007

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Two-dimensional movement control using electrocorticographic signals in humans

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G Schalk, K J Miller, N R Anderson, J A Wilson, M D Smyth, J G Ojemann, D W Moran, J R Wolpaw and E C Leuthardt

Abstract. We show here that a brain–computer interface (BCI) using electrocorticographic activity (ECoG) and imagined or overt motor tasks enables humans to control a computer cursor in two dimensions. Over a brief training period of 12–36 min, each of five human subjects acquired substantial control of particular ECoG features recorded from several locations over the same hemisphere, and achieved average success rates of 53–73% in a two-dimensional four-target center-out task in which chance accuracy was 25%. Our results support the expectation that ECoG-based BCIs can combine high performance with technical and clinical practicality, and also indicate promising directions for further research.

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