What is the opposite of multitasking? Reading? Maybe not....

In many popular articles, multitasking is contrasted with reading. "People multitask all the time, they never spend time reading a book." So, reading is not multitasking? Maybe it is. When you read a book, you almost never finish it in one sitting. This means that at some point you put the book down, proceed with other activities, and then later pick it up again. The fact that we can just continue reading, even after days of interruption, is quite a remarkable feat of memory, considering that in scientific studies, interruptions of only tens of seconds already produce strong interference results.
But even if we disregard the interruption factor in novels, reading a novel is often a multitasking challenge in itself because authors like to play games with the reader. Telling a story strictly linear can be boring, so authors sometimes reveal information out of temporal order, challenging the reader to keep all the facts straight. Or, the story is told from the viewpoint of several characters, and it is up to the reader to keep the different story threads apart.

Cloud Atlas: Hexatasking

An extreme example of a multitasking novel is "Cloud Atlas" by David Mitchell. The novel consists of six stories that have common elements and themes, but each of which has a completely separate plot (and writing style). The book starts with the first half of the first story, then proceeds with the first half of the second story, etcetera, until the sixth story, which is told in full, and is then followed by the second half of the fifth story, the second half of the fourth story, etcetera, until finally the second half of the first story.
In other words, halfway the reader has to maintain a representation of six partially finished stories. The challenge is to get into the second half of each of the remaining stories as they unfold, up until the second part of the first story. In my own experience this became increasingly harder, because more time and interfering text had passed in between. Nevertheless, Cloud Atlas is not a heavy read, and in fact quite an enjoyable book I would recommend to anyone. Reading: quite a feat of human multitasking.
Interestingly enough, the screenwriters of the movie version of Cloud Atlas decided not to follow the structure of the novel. Instead, they interleaved all six stories, ending with the end of the sixth story. And this was probably a good idea: if the movie would have been cut in the same way as the book is told, it would probably have become way too confusing (although it would be an interesting experiment to try out: can someone edit the movie in the book order an email it to me? I'd gladly run the experiment). Somehow the movie format requires refreshing the memory of the viewer every once in a while.
Why is there this difference between books and movies? Is it just the amount of time we spend on them? This cannot be the whole story, because the movie is approximately three hours, so if the movie would have been cut consistently with the structure of the book, the interruption in the first story would have been around 2.5 hours. When I read the book, the interruption was over a month. Even though reading the book may take longer than watching the movie (a factor of 5, perhaps?), the interruptions are even longer (a factor of 300, in my case).
Perhaps the difference is that we have different expectations, and therefore bring other memory strategies to bear. Maybe, when we read we are more proactive in building up a story representation than when watching a movie, in particular when most movies are designed to not require too much thinking anyway.