Evoked Potential tests

Had these today. Am curious especially about the Visual Evoked Potentials test. I experienced the test differently with each eye: with the right eye, the moving black and white checkerboard pattern soon began to grey out, losing a great deal of contrast so that it was all more or less grey. In addition it became very difficult to spot the yellow centre square which faded at the edges. With my left eye, these things did not happen at all and the moving checkerboard remained at constant contrast and sharpness. I still dont know if the fading was ‘real’ or just my perception as the tester evaded answering my question.

Also on the leg test, my little left toe would not start to twitch until the dial was turned up to a high level and I couldnt feel the pulse unless it was somewhat higher than for the other leg. Anyone know how these tests work and what these things signify if anything?