http://newsinfo.nd.edu/news/27476-walking-through-doorways-causes-forgetting-new-research-shows/

Event boundaries are deeply indicated as structural elements in our relationships with memory and orientation.

What we are learning now is the crude beginning of what we will discover about this, but, if you want to begin the exploration yourself, just realize that for most of our evolutionary history, there were few if any ‘doors’.

Neither were there ‘pages’ (which, like words, sentences, and paragraphs, are also implicated as physically obvious event boundaries…

Walking through doors acts as a cognitive event boundary:

http://newsinfo.nd.edu/news/27476-walking-through-doorways-causes-forgetting-new-research-shows/

Doors trigger reset:

http://www.lifeslittlemysteries.com/1939-walking-doorways-forgetting.html

Event boundaries:

http://pss.sagepub.com/content/18/5/449.abstract