Angelika Dimoka at Temple did some fascinating research on decision making using fMRI. When people were overloaded, what happened was much more complicated than just their ability to make decisions was degraded. What she found is that the part of the brain that is in charge of tough decisions just gives up and lets other parts of the brain make the decision. And it is even worse than the rational brain letting the emotional brain decide. To make good tough decisions, you need both the rational and emotional brains to participate. Prior research has shown that when the emotional centers are damaged, people can’t make rational decisions either. But in these fMRI studies, too much information made the dorsolateral pre-frontal cortex, which is what allows the rational and emotional brains to collaborate, just turns itself off. And it stops inhibiting the anxiety and frustration areas, so those run wild.
A lot of other research, for example some work by Sheena Iyengar at Columbia and Ap Dijksterhuis from the Netherlands (I have blogged about his work before), shows that trying to use too much information in a decision makes it worse, not better. We are much better off focusing on the few most important characteristics and ignore the others. One reason for this is that we have a limited working memory and we can only focus on a few characteristics at one time so it may as well be the most important ones. Another reason is that our brain has trouble assigning small importance values to attributes. So if a less important attribute is considered in a decision, it is probably going to be overweighted and therefore degrade the decision.
So what does all this tell us? When making important and tough decisions, you can spend as much time as you want collecting information and advice. But when it comes time to actually decide, shut off your email, your twitter, your TV, etc. and just cogitate for a little while. It will do you (and your dorsolateral pre-frontal cortex) a lot of good.