The NYT has a fairly skeptical article, "Taking Mental Snapshots to Plumb Our Inner Selves" (which is sorely lacking in credulity-inducing color brain scan images.) It's about UNLV psychologist, Russell T. Hurlburt, who studies how people's minds work by having them wear a buzzer that goes off randomly at which point they record whatever they were thinking about at that moment.

After hundreds of introspective interviews, Dr. Hurlburt still hesitates to generalize from his findings. But he has observed that the basic makeup of inner life varies substantially from person to person.

”My research says that there are a lot of people who don’t ever naturally form images, and then there are other people who form very florid, high-fidelity, Technicolor, moving images,” he said. Some people have inner lives dominated by speech, body sensations or emotions, he said, and yet others by ”unsymbolized thinking” that can take the form of wordless questions like, ”Should I have the ham sandwich or the roast beef?”

In a 2006 book, ”Exploring Inner Experience,” Dr. Hurlburt suggests that these differences may be linked to personality and behavior. Inner speakers tend to be more confident, for example, and those who think in pictures tend to have trouble empathizing with others.

It's interesting that we evolved to be so different mentally. Obviously, we're better off with a variety of thinking types, so we can get more mileage out of each one's overall brainpower through division of labor. Yet, I've been repeatedly assured that natural selection can't create a mechanism to diversify our portfolio of descendants, the way a mutual fund manager diversifies his portfolio of stocks to reduce risk. Most of the non-group selectionist theories for this diversity, however, don't really grab me, so I don't know what to think.

If had one word to describe how I think, it would be "prosaically." I'm primarily one of Hurlbert's inner speakers, with a single-threaded monologue. (No multi-tasking above the rudimentary. For example, although I can drive a car and carry on a conversation, I can't simultaneously drive, navigate to a new destination, and talk about anything other than navigating.) It's not a particularly articulate monologue, so writing requires a lot of rewriting for me, which the computer word processor, which I started using in 1981, made much more efficient for me. (I didn't have access to a word processor in 1983, so I did much less writing that year.)

Differences in thinking style may also help explain some aspects of mental illness. In studies conducted with Sharon Jones-Forrester and Stephanie Doucette, Dr. Hurlburt found that bulimic women experienced a clutter of simultaneous thoughts that could often be cleared by purging.

”Why is that? I have no idea,” Dr. Hurlburt said. ”But I haven’t found anything about it in the bulimia literature.”

That's weird, but it could prove helpful to someone.

It might be helpful to categorize writers. At the highest level of giftedness, the Nabokovs and Updikes have extraordinary multi-sensory receptiveness (input) to go along with their tremendous skill at expressing themselves (output). Waugh, despite all his aesthetic sensitivity, strikes me as more gifted on the output than the input side.