In a world of multiplying TV channels, hundreds of different types of jeans and salad dressings, and the constant pinging of e-mails and instant messages, the one resource that is increasingly scarce is our attention.

That observation has led some to dub the effort to make a business of capturing people's interest the "attention economy."

But the attention economy has an attention deficit: You can only pay attention to so many things. The number of intelligent choices you can make is limited. Giving something your attention takes time, and time is money. Or is it?

What to do about the attention deficit was the talk of two recent tech gatherings in the San Diego area, PC Forum and the O'Reilly Emerging Technologies conference.

In a speech earlier this week at PC Forum, author and psychologist Barry Schwartz pointed out the downside to having too much choice. It puts a strain on your attention.

"People are so overwhelmed with choice that instead of liberating people it tends to paralyze them," said Schwartz. "With all of this choice people may do better objectively -- they may get a better salad dressing, CD player or spouse -- but they will feel worse."

The superabundance of options raises expectations, he argues, and makes people blame themselves more often for choosing poorly.

As Schwartz puts it: "When there are only two types of jeans to choose from and the one you choose is not perfect, it's the world's fault. If there are 200 choices, and you don't choose the perfect one, it's your fault."

That sort of chooser's remorse is even more applicable to media and information on the Web, which is practically unlimited in its supply and mostly free. You may not be spending your money, but you are spending your time -- and how do you pick what to surf?

Companies that can help narrow people's choices and filter their attention are in high demand. Search engines like Google and Yahoo already do this in a crude way, but there is much room for improvement. For instance, one startup at PC Forum, Kosmix, is trying to take search to the next level by corralling results into very specific categories such as health, travel and politics. The goal is to help users who are researching, say, a trip to Paris complete with a stay at the Hilton find information about the hotel rather than the heiress.

Another startup, mSpoke, has created personalization software for website publishers that allows consumers to see why certain content and ads are being presented to them -- and correct erroneous assumptions about their preferences so the sites can become more useful over time. Amazon.com does this today for its book recommendations, pointing out the purchases that shaped its suggestions and letting you adjust the results there but the technology is not widespread.

The value that both Kosmix and mSpoke bring to the table is that they help to limit the options presented to people to only the most relevant ones.

The whole notion of an "attention economy," which was the official theme of last week's O'Reilly conference, revolves around the hope that technology can help solve our growing attention deficit. Google, after all, makes gobs of money by attracting and directing people's attention in useful ways. Now a host of startups want to cast themselves as solving similar problems.

Still, the metaphor can only go so far before it breaks. In order for attention to become the basis for an economic system, there would have to be some standard way of turning it into money.

We can do that today only to the extent that attention can be converted into something of value (through, say, advertising, speaking fees, or ticket sales).

The problem is that attention is a nebulous term. What is the basic unit of attention? It can't be based purely on time, because your time might be more valuable than mine, and your waking moments are surely more valuable than your sleeping moments. And time spent passively watching TV might be more valuable than time when you're distractedly reading a webpage and firing off e-mails.

In order to have an economy, you need to have some sort of common currency -- and "attention" is not one today.

There are some instances where you might be able to translate attention into money, when it becomes predictive of economic actions. For instance, if I spend 20 minutes building a virtual car on the Honda website I am probably more likely to buy a car than someone who just clicks on a Honda banner ad. Or if I've been spending two hours a day on Bankrate.com, chances are that I am ready to get a mortgage. But those types of activities only make up a very small portion of my attention. So is all my other attention worthless? And how would you ever measure it in a standardized way?

Turning time into money may prove a hopeless task. But the attention deficit still promises opportunity for startups. However much our attention is worth, we still don't have enough of it to go around. Companies and technologies that let us pay more attention to fewer things will be worth keeping an eye on.

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