“Change blindness is the striking failure to see large changes that normally would be noticed easily.”
Daniel J. Simons and Ronald A. Rensink, Change Blindness: Past, Present and Future, Trends in Cognitive Sciences, Vol.9 No.1 January 2005
“…observers often failed to notice large changes to photographs that were made during an eye movement . For example, 50% percent of observers failed to notice when two cowboys sitting on a bench exchanged heads! These shocking results inspired others to examine whether similar failures could happen in other ways, and in the absence of eye movements. In one of these new paradigms – the ‘flicker’ task  – an original and modified scene alternate repeatedly, separated a brief blank display, until observers find the change. Observers eventually find most changes, but can take an astonishingly long time to do so, even for large changes.”
If you don’t believe this, check out Rensink’s Java applet that illustrates what he calls the “flicker paradigm”. Two images flicker back and forth. With a 250 ms gap between images, I spent minutes looking for the difference. At 150 ms, I saw the difference almost immediately. With no gap, the difference is striking. Here is clear evidence that “no page refresh” apps are not simply less annoying, but clearer to understand.