How can we determine 
whether or not the 
achievement of constancy 
depends on prior experience? If 
the basis of constancy at issue 
is some stimulus relation, as is 
probable in the perception of 
lightness, there is no problem: 
Dependency on experience 
seems unlikely and, in fact, 
gratuitous. Given a certain 
stimulus basis for a perception, 
such as is surely true for the 
chromatic hues, what need to 
invoke a learning hypothesis? 
By the same token, if lightness 
is directly given by ratio of 
luminances, it seems quite 
plausible that lightness 
constancy is a direct outcome 
of determination by such a 
ratio. What little evidence 
there is on this question 
confirms this reasoning.