A Stanford professor whose quest for a bone-marrow match sparked "cheek swab" events in Palo Alto and around the world has died.

Nalini Ambady, 54, a professor of psychology, died of leukemia Oct. 28 without having found a donor.

Cheek swab events in the United States and near Ambady's birthplace in India did locate matches for seven other people in need of bone-marrow transplants. But of the roughly dozen people who were potential matches for Ambady, half ultimately turned out to be incompatible and the others chose not to donate.

Ambady was known for research showing that people can form accurate first impressions about others based on only seconds-long observations of their nonverbal behavior.

"Thin slices," as these quick impressions are known, have become a staple of social science textbooks and were popularized by Malcolm Gladwell in his 2005 bestseller "Blink: The Power of Thinking Without Thinking."

Born in Calcutta, Ambady earned her bachelor's degree from Delhi University. She came to the United States to study for a master's in psychology at the College of William and Mary and later earned a PhD in social psychology from Harvard University.

She taught at College of the Holy Cross, Harvard and Tufts University before joining the Stanford faculty in 2011.

Ambady argued that nonverbal behavior is important because it is a quick, efficient and relatively effortless way of obtaining information about others. At birth, humans respond to and produce nonverbal cues and nonverbal behavior that can serve as a primary mechanism of socialization across the lifespan. As she put it, "Nonverbal behavior offers a means of adapting to the social world."

She put these concepts to the test in one of her first publications, in 1993. She created 30-second, silent video clips of college professors delivering a lecture and asked people who had never seen the professors before to assess their teaching effectiveness. Remarkably, the scores from independent raters fell in line with those of students who had actually spent an entire semester in the professor's class. The results held even when she shortened the clip to 10, 6 and 2 seconds.

The work demonstrated that perceptual judgments made on the basis of very brief observations of nonverbal behavior can be surprisingly accurate and can influence a person's long-term impressions. The findings challenged established wisdom that intuitive reasoning is typically wrong and became a basis for the growing appreciation of the usefulness of nonconscious or "fast" thinking.

Ambady believed that even without conscious awareness, initial evaluative impressions can influence whom we sit next to in a subway, whom we hire for a job and, perhaps, even whom we marry. Her follow-up studies showed that similar snap evaluations can accurately predict a person's sexual orientation or political affiliation or a CEO's company profits.

In 1999, she received the Presidential Early Career Award for Scientists and Engineers from President Bill Clinton in recognition of this work. In February, she will be posthumously awarded the prestigious Carol and Ed Diener Award in Social Psychology, a recognition give by the Society for Personality and Social Psychology to scholars whose work has added substantially to the body of knowledge of the field.

Ambady was originally diagnosed with leukemia in 2004, but treatment drove the disease into remission. When it returned last November, doctors told her she needed a bone marrow transplant. South Asians – and minorities in general – are severely underrepresented in bone marrow donor registries in the United States.

Students and friends began fundraising drives to purchase and distribute the cheek swab kits used to identify potential donor matches, both in the United States and near her birthplace in India, where doctors believed there might be a better chance of locating a genetic match.

There are many reasons people ultimately decide not to donate, including cultural taboos or fears of pain or inconvenience, medical experts say. Donating bone marrow is only slightly more complex than donating blood, though it requires multiple visits. Some people's contact information simply falls out of the system, especially the case with college-age donors who frequently change addresses.

Ambady is survived by her husband, Raj Marphatia, and their daughters Maya and Leena.

Memorial services are pending. Memorial contributions can be made to the Nalini Ambady Memorial Fund, care of the Department of Psychology, Jordan Hall, Building 420, Stanford University, Stanford, CA 94305. Make checks payable to Stanford University.