for henry - it rarely gets discussed but it is a reasonable case that humans vary widely in many critical aspects of vision, as we see resulting from many factors such as diet, experience, health, lifestyle and demographics. So much so that many individuals at one end of the distribution struggle to see (figuratively or literally) what those at the other end are talking about.
This is why solid empirical studies matter - they give us a good sample size to even out such effects across a large number of observations, sufficiently large to enable statistical validity to be inferred.
Luka (denoir) did just such a study here, to verify that a large proportion of viewers could identify Zeiss lenses from near equivalent Canon lenses. Empirical data is never enough to dispel the feedback each person may experience from their own vision ('seeing is believing' right?) but these two factors - individual variability and study results - might give people cause to reflect.
It's a personal view, but it seems a reasonable expectation that people with long exposure to situations requiring excellent depth perception are more likely to see the presence or absence of cues in images that indicate depth or three dimensionality than those without such experience.