For example I couldn't tell the text at all in any of the four tags, including the "hard to read" or "quite unreadable".
Edit: I see from the FAQs there's some kind of display calibration portion at the start of the test; should have read the website more carefully before asking!
For what it's worth, I couldn't tell the difference either. All of them were completely incomprehensible.
> What can cause a contrast sensitivity deficit? > Many things can affect the ability to perceive contrast. These include nutritional deficiencies, the consumption of alcohol, drug/medication use, and exposure to endogenous or exogenous neurotoxins and/or biotoxins, including volatile organic compounds (VOCs), venom from animal or insect stings or bites, some species of mold and the mycotoxins and microbial VOCs they produce, cyanobacteria, dinoflagellates (particularly Pfiesteria and Ciguatera), apicomplexans, parasites, heavy metals like mercury and lead, and the pathogens responsible for Lyme disease and its common co-infections. For more information, see our Research resources.