In Brain Rules, John Medina points out that the brain cannot multitask:
We are biologically incapable of processing attention-rich inputs simultaneously.
I like the specificity of that sentence and how it gets the point across in so few words.
Yes, we can do more than one thing at once (i.e., breathe and type), but breathing is not an attention-rich task. Our society would orders of magnitude less advanced if that were the case.
No, we cannot do things like lead a phone conference while checking email and responding to IMs (though I’m sure many of my and your co-workers have gotten good at making you think they can do this).
I love the picture they used in the Lateral Action post: