What makes a face look human? Some researcher says it’s all in the eyes.

“There's something fundamentally important about seeing a face and knowing that the lights are on and someone is home,” said Thalia Wheatley of Dartmouth College, in a statement.

She cowrote a study with graduate student Christine Looser that was published in Psychological Science, a journal of the Association for Psychological Science.

Wheatley said humans can see faces in the moon, a piece of toast, two dots and a line for a nose. But no one believes they are truly alive.

For the study, the pair photographed doll faces. They paired them with similar-looking human faces and used morphing software to blend them in a series of photos.

Volunteers were asked which ones were human and which ones were dolls. The tipping point, when they decided they were alive, was about two-thirds of the way along the continuum, closer to the human side. Another experiment found that the eyes were the most important feature for determining life.

Researchers said the results suggest that people scrutinize faces, particularly the eyes, for evidence of life.

“I think we all seek connections with others,” Wheatley said. When people see life in a face, they think, “This is a mind I can connect with.”