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Brainwaves on my mind

Is this the title of a song for bioengineers?

By Chuck Newcombe

October 2011

Actually, this column is a follow-up to my recent column entitled “Say or Press One.”

The subject of that column was mostly speech synthesis and voice recognition, but it ended with some examples of recent promising research on direct brain control of computers, enabling communications and even control of devices such as wheelchairs.

Basic brain wave detection

Research scientists and members of the medical community have long (since 1924) had the capability to read electrical signals related to brain activity using a device known as an electroencephalograph (EEG). This device uses 10, 20, or more electrodes on the scalp to sense and record actual neural activity in the brain.

In 2009, some games became available - names like Star Wars the Force Trainer™ and MindFlex®. These games have head-mounted electrodes touching the scalp to interpret some basic brainwave patterns, according to their makers. The sensor headgear contains a sophisticated signal processing chip, made by NeuroSky, which amplifies and filters the detected signals, sending them by radio to a game console where they control the speed of an air blower to adjust ball height in a column of air.

Players are directed to will a ball to rise or fall on an air column to certain target levels and, with practice, most are able to achieve some degree of success. It’s amazing to watch someone improve this capability without really knowing just how they did it. It’s all about positive feedback - when they see the results they are looking for, they somehow train themselves to repeat the effect. And, in the case of the Force Trainer, Yoda cheers them on to success in a series of challenges.

EEG band frequencies

I wanted to learn more

The idea was to have a subject running one of these games while I recorded the signals from the electrodes on his scalp. I hoped to isolate the frequency bands used to control the air column in the game. My primary areas of interest were the alpha and beta waves (listed in bold at the right), which correspond with relaxation/meditation and concentration/attention, respectively.

Unfortunately, on further investigation, I discovered that the signals I wanted to record were in the microvolt range.

Does Fluke have a meter that can record an EEG?

The answer is, “Not exactly.” Detecting and recording EEG waveforms requires specialized high gain differential amplifier technology. I did find an example of the type of amplifier needed (not manufactured by Fluke) in the Fluke Biomedical design labs, but that still doesn’t provide a convenient, easy-to-read information display.

Bring on the ScopeMeter® tools

The ScopeMeter® 190 Series II oscilloscopes have a basic input sensitivity of 2 mV/div. They also have bandwidth limiting filters, waveform averaging, and spectrum analysis capabilities. So, I decided to see if I could use some combination of these in a ScopeMeter® 199C to read signals similar to the raw brainwave signals being picked up by the game headgear. The signals I was looking for ranged in frequency from 1.0 to 50 Hz. So, I theorized, if I had a suitable instrumentation amplifier, and could amplify the signal from electrodes connected to the left forehead and left ear lobe by at least 1000, I should have adequate signals to be analyzed by my 199C.

Synthesizing my test signal

It so happens that I have a function generator that can output sine, triangle, and square waves from less than 1 Hz to over 1 MHz. The output signal level is best controlled in the 1 to 3 volt range, so I had to build a resistive divider to get a signal in the 30 mV range. Now I was ready to check out the capabilities of the ScopeMeter®.

I adjusted the generator to put out a triangle wave at 7 Hz, just below the bottom of the range for alpha waves. Ideally I would set the rms level of a sine wave to 2 mV and use a direct input scope probe, as would be done with an instrumentation amplifier. I only had a 10:1 probe, so I set the level to 20 mV and then connected the A input probe of the 199C to the divider output.

The setup of the 199C

The setup of the 199C

After getting a stable 7 Hz signal on my screen, I pressed the A input button and selected INPUT A OPTIONS. There, I moved to the Bandwidth section and selected 10 kHz (HF Reject).

Next, I pressed the SCOPE button and selected WAVEFORM OPTIONS

Here, I turned off Glitch Detect, and selected Mathematics.

Finally, on the Mathematics menu, I selected Spectrum and accepted the recommended default Auto Window setting.

ScopeMeter 199C Spectrum Screen

ScopeMeter 199C Spectrum Screen

This is the Spectrum screen I saw at the conclusion of my experiment. You can see three spectral lines between 7 and 40 Hz, right where I would expect to see output from an instrumentation amplifier connected to electroencephalograph probes.

I’m satisfied that a ScopeMeter product could be useful in such a test.

May the Force be with you.

Note: For more information on brainwave recording go to the following link. You will find reference to the Neurosky company that I mention at the beginning of this article. Electroencephalography Comparison Table »