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C. Barber, Y. Wen, L. Wang, R. Kakigi; Towards Optimisation of the Multifocal Visually Evoked Response by using Graduated Checkerboard Stimulus Patterns . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4110.
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Purpose: To use the multifoocal visually evoked magnetic field (mfVEF) in comparing the efficacy of regular, graduated check size and graduated element size checkerboards in eliciting approximately uniform amplitude responses from across the visual field and to relate these to anatomically-based predictions Methods: A VERIS multifocal system generated one of series of custom checkerboard patterns and this was projected into a magnetically shielded room. The series comprised either a regular array of 64 elements, all containing checks of the same size, or a similar array containing checks whose size increased with eccentricity, or an array (of either 40 or 52 elements) whose element size and check size both increased with eccentricity.. All subtended 16° visual angle at the subject. 32-channel magnetoencephalogram (MEG) signals were recorded using a Magnes system and a special multi-channel VERIS computer (EDI Inc). Recordings were made from 4 volunteer subjects with normal or corrected-to-normal vision and compared with responses to the usual dartboard stimulus. Results: Clear mVEF waveforms were recorded in all cases from stimulus elements adjacent to the fixation point, but regular checkerboards, even with increasing check sizes, did not generate good responses from more eccentric stimulus element locations. Doubly-graduated (check size and element size) checkerboards produced good responses over a much wider area and were better than the usual dartboard responses. Pattern reversal stimulation produced bigger responses than did pattern onset. Response amplitudes agreed reasonably well with anatomical predictions Conclusions: Responses elicited by graduated checkerboard stimulus patterns exhibit superior uniformity over the stimulus field. Further, they lend themselves well to comparison with conventional pattern visual evoked responses and are free from any confounding factor due to stimulus orientation.
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