It is argued that a previous study showing the parallel lines illusion is stronger in adulthood than in adolescence or old age is methodologically sound. Further, this finding does not necessitate a defense of assimilation theory based on epistemology that links the phenomenal properties of illusions to the techniques of measurement. Rather, it is suggested that Pressey's 1974 and 1987 hypothesis that all illusions of assimilation decline from childhood to adulthood mistakenly extends the decrement into adulthood when in fact the decrement occurs only between the ages of 6 and 10 years.