What is the non-parametric version of two-way ANOVA?
I am a little rusty on this, but I seem to recall that for these kinds of 2×2 designs with non-parametric data the Mantel-Haenszel chi-square test is the way to go. If you’re cramming this into a 2×2 table then you must be stratifying the dependent results (# of errors on visual testing) into PassVisualTest and FailVisualTest categories. This may not be the best way to go about this. The (Wilcoxon)-Mann-Whitney U test is a special or degenerate case of this test so it may also be appropriate. It’s worth knowing that you have to have a pretty large sample size for either of these tests to have a decent chance of detecting a significant result. If any of the 2×2 cells contain less than 5 subjects, the chi-square test is likely to produce a type II error (failure to detect a true difference between the groups); the Mann-Whitney test likewise requires a fairly large sample, 50-100 or so in each wing to detect reasonable differences. I would strongly caution you about transforming data to f
