The pattern-pulse multifocal visual evoked potential.

PURPOSE

To define the pattern-pulse multifocal visual evoked potential (PPMVEP) and determine its characteristics in a sample of normal subjects in terms of amplitude of response attainable, the variation in waveform across visual field, and distribution of potential over the scalp and to compare pattern-pulse with contrast-reversal multifocal stimuli.

METHODS

VEPs were obtained by concurrently stimulating 60 regions of a cortically scaled dartboard with pulses of pattern contrast. Responses were recorded from normal subjects, by using a 32-channel electroencephalogram recording system, and elementary responses to each region were estimated by multiple regression of each of the response channel signals on stimulus signals. Left-eye, right-eye, and binocular viewing conditions were concurrently tested by dichoptic stimulation. A direct comparison was then made with contrast-reversal stimulation.

RESULTS

Response waveform sets for 12 subjects varied in maximum amplitude from 1.8 to 6.8 micro V. A stereotypical distribution of waveforms held in most subjects, depending primarily on the polar angle location of the stimulus within the visual field. In a direct comparison with a contrast-reversal multifocal analysis, the pattern-pulse responses had similar waveforms and scalp topography, but were 15 times larger in amplitude. Root mean square (RMS) signal-to-noise ratio (SNR) was 1.9 times higher with pattern-pulse stimulation, corresponding to a reduction of 73% in recording time to achieve the same SNR.

CONCLUSIONS

The PPMVEP can simultaneously characterize 60 regions of the visual field for both eyes in less than 7 minutes. A general methodology is illustrated that allows multifocal analysis with flexible choice of stimulus conditions.