It's common knowledge that observers make snap judgments, within three seconds, based on someone's appearance. But Baumgartner's work isn't just about dressing to impress.

There's increasing evidence that how a person dresses can influence - not just reflect - the wearer's own psychological processes.

One recent study on "enclothed cognition" - the effects of clothing on cognition - looked at the effect of wearing a lab coat on cognitive performance. In the study, conducted at Northwestern University and published on the website of the Journal of Experimental Social Psychology, wearing a lab coat improved study participants' performance on an attention task. In a second part, performance improved if participants were told the lab coat they were wearing was a doctor's coat. If they were told it was a painter's coat, their performance did not improve.

If appearance were purely superficial, observing it wouldn't be standard procedure for psychologists in therapy sessions, Baumgartner said.

"Part of our initial discussion is to note clients' physical appearance when they first come in. ... If their dress has changed or they're failing to take care of their hygiene, it's a clinical indicator that something might be going on."

Baumgartner pursued her doctoral degree in clinical psychology while working on the sales floor at Ralph Lauren to pay the bills.

"The two kind of came together. Women had meltdowns in the dressing room, but it had nothing to do with clothing. What else was it? Obviously there was a lot more there than the clothes."

Nowadays she might encourage therapy clients to dress "as-if." "Often, if you can think like the person you want to be, you can learn how to reach that point."

The Tao of shoes

"Women From the Ankle Down" focuses less on psychology and more on history. But the two intertwine, said author Rachelle Bergstein.

When people hear about her book, she said, they often ask, "What's the deal with women and shoes? Why do they love them so much?"

Her answer: "It's complicated."

For starters, women can get away with more fantasy in footwear than in clothing, and shoes don't raise body-image insecurities the way clothing often does, she said.

"The best way to summarize it would be to say that shoes have, through various historical connections, become a shorthand for status, sexuality and identity. And that's really appealing to women."

Women's complicated relationship with shoes, particularly heels, dates to 18th century Venice, when women wore shoes as high as 20 inches, possibly to keep their clothes off the filthy streets, Bergstein said, though at the price of walking independently. Servants escorted them.

Even further back, Louis XIV and his men were the only ones allowed to wear red shoes, Bergstein noted.

Red shoes' association with status is echoed in the movie version of"The Wizard of Oz"and the fairy tale "The Red Shoes."

It may help explain why, today, the red soles of Christian Louboutin footwear tack a few hundred dollars onto the price. "At this point, everyone, including my dad, recognizes that the red sole means Louboutin, which means expensive," Bergstein said.

Which brings us back to psychology. It's not just red shoes that make an instant impression; heels in general carry a great deal of psychological weight.

"Women will tell you they feel empowered by being taller. In a business place, it's to women's advantage to be able to look men in the eye," Bergstein said. "On the other hand you have women saying, 'Why is it empowering for my walk to be invented? Being empowered should be being in shoes I can walk my fastest in.' That's an argument we're not going to solve any time soon."

Baumgartner shares her point of view in "You Are What You Wear."

"While some pieces get attention for all the wrong reasons, others enhance our femininity without giving it all away," Baumgartner writes. "If you want to feel instantly sexier without the compromise, slip on the stiletto."