Bring up the subject of pacifiers among new parents, and you'll probably spark a spirited conversation that will wake up every sleeping baby within a block or so.

Now, a UW-Madison study is likely to fuel even more debate about the trusty old nuk. Or nuki. Or binky. Or na-na. Or whatever you have chosen to call the device that serves as a remarkably effective volume control for most babies.

Paula Niedenthal, a psychology professor and lead author of the study, found that boys who used pacifiers as babies scored lower on tests that measured their emotional development. According to the research, the pacifier prevented babies from mimicking the facial expressions of those with whom they were interacting. And that mimicry, other research has shown, is important because it triggers activity in the brain that allows one to actually feel the emotion being expressed.

"When you make that facial expression yourself, you start developing those feelings yourself," Niedenthal said.

Niedenthal said studies on girls did not show the same phenomenon. She said that may be because of societal norms that prompt parents to work harder at encouraging the expression of emotion in girls.

Niedenthal has specialized in studying the connections between emotions and physical behaviors such as expressions. She compared her work with babies and pacifiers to studies that have shown people who use Botox, which paralyzes facial muscles, have a more limited range of emotions and also have difficulty recognizing the emotions behind others' facial expressions.

But her current research had a much less scientific origin. Her own three boys did not use pacifiers, Niedenthal said. She recalled a dinner at which her 3-year-old son was throwing a fit. She noticed that another child at the table, who was using a pacifier, did not respond to her son's flailing tantrum.

"The parents took the pacifier out, and the child still did not respond," Niedenthal said. "That's when I got the idea for this research."

To test her theory that a pacifier prevented mimicry of facial expressions, Niedenthal first studied 6- and 7-year-old boys who had used pacifiers by having them watch videos that would normally elicit facial mimickry. She found that the boys with a history of pacifier use were less likely to try out the expressions worn by those in the video.

Also, Niedenthal studied college-age men who reported more pacifier use as babies (she had them call their parents to double-check). The men took a standard test to measure emotional intelligence and their decision-making based on assessing others' moods. Even taking into account anxiety or attachment issues, the men who had used pacifiers scored worse on the tests, according to Niedenthal.

Niedenthal is keenly aware that her study is likely to stir up more than a few breakfast table and water cooler arguments.

"People have very strong opinions," Niedenthal said of pacifiers.

Brook Fennell, a registered nurse at St. Mary's Hospital who works with newborns and new moms, said the hospital makes no recommendation one way or another on pacifiers. She does recommend that moms who breast-feed think twice about pacifier use because it can affect a baby's ability to suckle effectively. Also, she added, the American Academy of Pediatrics advises the use of pacifiers at night to lessen the chance of sudden infant death syndrome.

There are, Fennell said, lots of varying opinions. "Any lay person or medical person is going to give you their take on it," said Fennell. "Every parent has to decide what works for them."

Carleen Hanson, a pediatrician who works at the Meriter West Washington Clinic, agreed and said the decision on pacifiers is personal. Clearly, however, some babies "are definitely orally soothed" by a pacifier, Hanson added.

Elizabeth Lipps is on the front lines of this particular debate. She's a new mother. And on Tuesday she was wheeling her 2-month-old son, Camden, through the aisles of Toys R Us on Madison's West Side. Camden was snoozing peacefully, and on his tiny chest rested a pacifier.

It was not difficult at all to understand the expression on Lipps' face after she was told about the study and asked whether she would consider permanently plucking Camden's pacifier. It was the sort of expression you might see on the face of someone who had just been asked to give up a million-dollar winning lottery ticket.

Gazing happily at her sleeping baby, Lipps offered a quick, firm reply.

"I probably won't even read the research."