So, this article by Randolph E. Schmid of the Associated Press discusses the results of a study on multitasking and learning. The study used brain imaging technology to watch activity in the brains of 14 subjects as they tried to learn new information with various sorts of distractions.
I'd be the first to agree that yes, focusing on more than one thing at a time means you can't do everything with full concentration (though certainly some people manage to do this quite efficiently, depending on the tasks). And recent brain research is fascinating.
However, I have a problem with how they're defining "learning." Granted, any scientific study of this kind--extremely narrow and precise--has to use precise, measurable concepts and goals. But here's what Schmid says: "As Poldrack explains it, the brain learns in two different ways. One, called declarative learning, involves the medial temporal lobe and deals with learning active facts that can be recalled and used with great flexibility. The second, involving the striatum, is called habit learning."
He uses the example of a phone number: in declarative learning, I would purposefully memorize the number. Kind of like when we had to memorize the multiplication tables, or when one is preparing for a test of knowledge, like a quiz on conjugation of German verbs. In habit learning, I'd come to remember that phone number by using it a lot.
But these are very narrow definitions of learning--useful for describing how we incorporate discrete bits of data into our lives, but now how we combine that data to create meaning. How we work to make sense of the world around us. How might multitasking impact those kinds of learning? Other research has suggested that such learning is best understood as a social activity--is conversation with multiple people multitasking?