In a study that has been getting a lot of attention recently, American and Japanese college students were required to judge the facial expressions of digitally altered photos. The American students looked primarily at the mouths, while the Japanese students looked primarily at the eyes. (via Ars Technica.)
This is supposed to explain why Japanese on-line writers prefer emoticons like these:
*_* ;_; ^_^
while Americans prefer things like
all of which can lead to cultural misunderstandings.
But it is obviously is relevant to the “big eyes” question. To Japanese artists and fans the eyes are much more important for conveying expressions.