The information flowing into our working memory at any given moment is called our 'cognitive load.' When the load exceeds our mind's ability to store and process information- when the water overflows the thimble- we're unable to retain the information or to draw connections with the information already stored in our long-term memory. We can't translate the new information into schemas. Our ability to learn suffers, and our understanding remains shallow. Because our ability to maintain our attention also depends on our working memory- 'we have to remember what it is we are to concentrate on,' ... Experiments indicate that as we reach the limits of our working memory, it becomes harder to distinguish relevant information from irrelevant information, signal from noise. We become mindless consumers of data."
The Shallows, pp. 124-25