Vicki explained it very clearly and well. That is the test I had this week--infrared cameras, goggles, cool water, warm water, ice water. And it proved I had total loss of balance function on both the left side, where it was expected as I had a labyrinthectomy over 10 years ago, and on the right side, where it was NOT expected, since I had some hearing (<40%) in that ear. I am not sure of the impact of antivirals. I did three runs of them years ago, extremely high doses for two weeks, then three months, no improvement. The antiviral was Valtrex, a form of acyclovir. I would ask your doctor about it before your VNG, for any of you out there. I assume that on every visit, you bring a list of your current medications to your doctor. That is essential in assessing where you are. As I have noted in other threads, my doctor is Dr. Jennifer Derebery, of the House Ear Clinic in Los Angeles. She is a goddess to me. She really knows our illness, and is a very nice person as well.