> However, some sites have a default preselected size for products — for example, a 39 x 27 inch poster size selected by default — which enables users to add a product to the cart without reviewing and selecting the size option at all on the product page. During our eye-tracking study, we observed that several users at AllPosters never even looked at the size drop-down, instead going with whatever size was the default.

Sorta have to question now whether such usability studies show real behavior of people. Because I can't conceive of someone buying a poster and never thinking whether it would fit in the space on the wall. At least if the person isn't drunk.