We have succeeded in taking Visual Evoked Potentials (VEP’s) using the Discovery 24E 24-channel EEG.
We used EPrime to deliver the stimuli and put the synchronization data into EEG data channels 23 and 24.
We used EEGLab to recognize the timing events, extract the epochs, and plot the Averaged Visual Evoked Potentials.
The image below shows the sync. pulses (fixation is on channel 23, and stimulus is on channel 24. We triggered on the falling edge (onset) of the stimulus to extract the epochs.
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The image below shows an Averaged Visual Evoked Potential from site O1 with a P300 marker at 300 milliseconds
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The image below shows a Visual Evoked Potential with the N145 component marked:
EEGLab is free to download from the University of California San Diego at http://sccn.ucsd.edu/eeglab/ . It is written in MATLAB and is open-source, so that MATLAB users can download the source code and develop further applications. EEGLab is also programmable in itself. EEGLab was written at the Swartz Center for Computational Neuroscience by Scott Makeig and his team.
EPrime 2.0 is downloadable from www.pstnet.com and there is a free demonstration that can be used. This example was done with the free demonstration program. The EPrime 2.0 control file used in this example is attached to this article.
A YouTube video showing the data acquisition and stimulation is at: http://www.youtube.com/watch?v=esQPi_hJgLc
Interested Discovery owners are able to record and compute evoked potentials without having to make any additional software purchases. A special cable is required to send the stimulation information to the Discovery via. an optically isolated connection between the PC parallel port and the Discovery inputs to channels 23 and 24.
The attached pdf file “EPs_1.pdf” shows the Discovery EP alongside the ACNS standard EP. All the components are present. The Discovery EP has additional components because it was stimulated at a 1/sec repetitive rate, hence is really a slow steady-state evoked potential. It also contains both on-response and off-response because the flash had a duration of 100 milliseconds. So this is a complex EP, but compares properly with the standard pattern-reversal EP.
Additional files can be found at: http://www.brainm.com/software/pubs/eps/
