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Adult memories are heightened by both joy and misery.

But babies apparently have one-track minds, according to researchers at Brigham Young University.

A new study published in Infant Behavior and Development found babies are more likely to remember something associated with positive feelings. Negative emotions did not produce the same memory-inducing results.

"You and I can remember both positive and negative events — the death of a loved one, divorce, the birth of a child," said lead author Ross Flom, a BYU psychology professor. "What we showed was actually only the positive events affected the babies' memories."

Flom and university researchers watched how a group of 5-month-olds responded to a series of stimuli. The babies were put in front of flat-paneled monitors and shown recordings of people speaking with either happy, neutral or angry voices. Immediately after the emotional speech, the babies were shown geometric shapes.

To test the infants' memories, researchers followed up by showing the babies the same geometric image alongside a new image five minutes later and a day later, monitoring the infants' eye movements and how long they focused on the image.

The babies were significantly better at recognizing the geometric image if it had been associated with the happy voice.

"That was a little bit asymmetrical of what we thought would happen," Flom said.

Researchers have a couple of theories about why babies are better at remembering happy experiences. Flom said it's possible infants process positive feelings differently than negative. It's also possible babies haven't been exposed to much negative emotion at a young age.

Five months is a benchmark for infant memory. Studies of younger babies have shown they have developed memory, but cannot discriminate as well between positive and negative emotions.

"This is as young as you can possibly go," Flom said.

BYU assistant psychology professor Brock Kirwan plans to follow up with noninvasive neurophysiological fMRI scans of infant brains during memory testing.