Development of a computerized EEG imaging system with a personal computer.

The authors developed a computerized electroencephalography imaging system with an IBM PC AT. The EEG signals amplified with a 16 channel EEG machine were digitized at 51.2 Hz (512 samples per epoch). The shifted DC potential and 60Hz artificats were removed by a high pass filter and 60Hz notch filter. A window function consisting of a 10% cosine taper was obtained by weighting the points at either end of the epoch by a cosine bell. A fast Fourier transform was applied to every epoch and the power spectrum estimates were computed in 0.39 Hz steps. The activity estimates for the delta, theta, alpha and beta bands were computed by summimg adjacent values. The outline of the top-down maps was formed from a series of sagittal cuts, then 32 electrodes were placed on the map. A file was created which contained a table of weighting parameters for calculating the interpolated values for every point within the outline. Each weight was in inverse linear proportion to the distance of the pixel to the nearest four electrodes. The map was finally generated with computation of the spectral EEG in each pixel according to the weighting parameter. The functioning of this system was tested with a functional generator and a human subject.