Other people can help us compensate for our mental and emotional deficiencies, much as a wooden leg can compensate for a physical deficiency. Specifically, other people can extend our intelligence and help us understand and regulate our emotions. I've argued that such relationships can become so close that other people essentially act as extensions of oneself, much like a wooden leg can serve as an extension of oneself. When another person helps us in such ways, he or she is participating in what I've called a "Social Prosthetic System." Such systems do not need to operate face-to-face, and it's clear to me that the Internet is expanding the range of my Social Prosthetic Systems. The Internet is already an enormous repository of the products of many minds, and the interactive aspects of the evolving Internet are bringing it ever closer to the sort of personal interactions that underlie Social Prosthetic Systems.

Even in its current state, the Internet has extended my memory, perception, and judgment.

Regarding memory: Once I look up something on the Internet, I don't need to retain all the details for future use — I know where to find that information again, and can quickly and easily do so. More generally, the Internet functions as if it is my memory. This function of the Internet is particularly striking when I'm writing; I no longer am comfortable writing if I'm not connected to the Internet. It's become completely natural to check facts as I write, taking a minute or two to dip into PubMed, Wikipedia, or the like. When I write with a browser open in the background, it feels like the browser is an extension of myself.

Regarding perception: Sometimes I feel as if the Internet has granted me clairvoyance: I can see things at a distance. I'm particularly struck by the ease of using videos, allowing me to feel as though I've witnessed a particular event in the news. It's a cliché, but the world really does feel smaller.

Regarding judgment: The Internet has made me smarter, in matters small and large. For example, when writing a textbook it's become second nature to check a dozen definitions of a key term, which helps me to distill the essence of its meaning. But more than that, I now regularly compare my views with those of many other people. If I have a "new idea," I now quickly look to see whether somebody else has already had it, or conceived of something similar — and I then compare and contrast what I think with what others have thought. This inevitably hones my own views. Moreover, I use the Internet for "sanity checks," trying to gauge whether my emotional reactions to an event are reasonable, quickly comparing them to those of others.

These effects of the Internet have become even more striking since I've used a smart phone. I now regularly pull out my phone to check a fact, to watch a video, and to read blogs. Such activities fill the spaces that used to be dead time (such as waiting for somebody to arrive for a lunch meeting).

But that's the upside. The downside is that when I used to have those dead periods, I often would let my thoughts drift, and sometimes would have an unexpected insight or idea. Those opportunities are now fewer and farther between. Like anything else, constant connectivity has posed various tradeoffs; nothing is without a price. But in this case, I think — on balance — it's a small price to pay. I am a better thinker now than I was before I integrated the Internet into my mental and emotional processing.