Carl and Richard circle back with Mark Miller for a whirlwind discussion on the biology of user interface design. Actually, it's the biology of humans as it relates to UI, focusing (no pun intended) on the eyes - how exactly does eyesight work? What cultural and psychological conditioning affects how you see? And ultimately, how can we apply the understanding of eyesight to make applications that are easier to use, easier to understand, and more enjoyable? Mark has years of experience in building great UI, and has distilled the core elements down to the biology of the user!