The depth of our intelligence hinges on our ability to transfer information from working memory, the scratch pad of consciousness, to long-term memory, the mind’s filing system. When facts and experiences enter our long-term memory, we are able to weave them into the complex ideas that give richness to our thought. But the passage from working memory to long-term memory also forms a bottleneck in our brain. Whereas long-term memory has an almost unlimited capacity, working memory can hold only a relatively small amount of information at a time. And that short-term storage is fragile: A break in our attention can sweep its contents from our mind.
The penalty is amplified by what brain scientists call switching costs. Every time we shift our attention, the brain has to reorient itself, further taxing our mental resources. Many studies have shown that switching between just two tasks can add substantially to our cognitive load, impeding our thinking and increasing the likelihood that we’ll overlook or misinterpret important information. On the Internet, where we generally juggle several tasks, the switching costs pile ever higher.