Baring a fault in our visual cortex or optical systems - an optical illusion, in other words - how is determining that Black is Black or that two lines are the same length any different from mathematical statements? There's a bit in the sequences on why 2+2=4 isn't exactly an unconditional truth. The thought processes that go into both include checking your perceptions, checking your memory, and checking reality.

Maybe 2+2=4 is too simple an example, though; it would be downright Orwellian to stand in a room and listen to a group of people declare that 2+2=5. On the other hand, imagine standing in a room with a bunch of people claiming that there aren't an infinite amount of prime numbers - it might be easier to doubt your own perceptions.

Anyone else want to weigh in on this? Does Asch's methodology effect conformity?