Jean Berko Gleason’s academic homepage:

A pioneer in the field of child language research, Jean Berko Gleason’s wugs and nizzes remain relevant more than half a century after their first appearance. There is a link on this site to Berko (1958), the original article in Word, which is still worth reading. You can also access the original pictures of her novel creatures. Don’t expect great art, but do expect great ingenuity and a lasting influence.