The pattern-pulse multifocal visual evoked potential.
OBJECTIVE
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.
James
Andrew Charles
AC
Center for Brain and Cognition Research, Unit 5549, National Center for Scientific Research (CNRS) and Paul Sabatier University, Toulouse, France. andrew.james@anu.edu.au
D000328:Adult; D015350:Contrast Sensitivity; D005074:Evoked Potentials, Visual / Q000502:physiology*; D006801:Humans; D008875:Middle Aged; D015348:Vision, Binocular; D014793:Visual Cortex / Q000502:physiology*; D014794:Visual Fields / Q000502:physiology*; D014795:Visual Pathways / Q000502:physiology