Tuesday, December 27, 2011

Rationality in Multitasking

There is typically a big gap between the tasks studied in psychological experiments and real-life cognition. This is because psychologists want to study the individual psychological functions in great detail, and therefore develop tasks that try to isolate these functions. Although this offers a wealth of information, the danger is that the interaction between those functions is not well understood. For example, in the example of the attentional blink that I discussed earlier, researchers still do not agree on whether the phenomenon is due to a attention, memory or control.

When Dario Salvucci and I were working on our book on multitasking, we also found an example of this gap. Observational studies had shown that the cost of interruption can be very large, in terms of tens of minutes. However, interruption costs in experiments are typically in the order of only a second. To study interruption behavior at a more realistic scale, Dario and his graduate student Peter Bogunovich designed an experiment that was in between real life and a basic experiment. Subjects had to answer emails for which they had to look up information using a web browser. Occasionally though, a chat window blinked in the background. If subjects clicked on this window, a question about movie preferences was asked which they then had to answer.
The important aspect of the task was that subjects had complete freedom in when they wanted to switch between email and chat, something that is typically not done in experiments. They could switch to the chat right when it would come up with a new question, or they could wait until they were done with the current email. The mail task was structured in such a way that information had to be remembered. For example, in the example in the picture, the price of the mp3-player Killor U-32 had to be looked up, which takes three clicks in the web browser. In the real experiment (as opposed to the picture) the windows were always on top of each other. So, when you have just clicked on "mp3-player" in the browser, it is not very clever to switch to the chat, because then you probably have forgotten "Killor U-32" when you get back.
It turned out that the subjects in Dario's experiment were indeed smart about this, and continued on the mail task until they reached a smart switch point, a point during which they did not need to remember any information.

Together with Jelmer Borst and a group of project students (Joost Timmermans, Anita Drenthen en Tom Janssen), we redesigned the experiment in order to try to tempt subjects into switching to the chat window at moments that information from the email had to be remembered. We did this by introducing delays in the web browser (after clicking a link it took a few seconds before the subsequent page appeared) and the email program (it took a second for an email to load). As a result, a substantial number of subjects now switched from mail to chat during a delay in the browser, at a moment when information had to be kept active. Moreover, the average time needed to answer an email with delays was longer than without delays, even if all the delays were subtracted from this time first. In the strongest condition the extra cost was more than 6 seconds (ok, still not minutes, but better than just a second). In other words, subjects would have been better off if they had just waited during delays instead of making a switch. Trying to use the waiting time for something else turned out to decrease efficiency instead of increasing it.

What these experiments show is that people are typically smart about their choices in switching from one task to another. But delays can surely thwart this rationality. Apparently, we'd rather act than wait, and that is probably why I prefer taking the bicycle over waiting for the bus, even though the latter option might get me there faster.

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