Researchers at Penn State are using new statistical analysis methods to compare how we observe infants develop new skills with the unseen changes in electrical activity in the brain, or electroencephalography ( EEG ) power. They found that most babies appear to learn new skills in irregular bursts, while their EEG power grows steadily behind the scenes. The study was published in the  Child Development 

A total of 28 six-month-old infants were recruited and brought to the lab eleven a month until they turned one year old. During each visit, the baby participated in a cognitive test called the "a-not-b task," designed in the 1950s to measure an infant's understanding of object permanence: knowing something exists even if it's out of sight.

In the task, a researcher put a cardboard box with two wells – A and B – across from the infant . The researcher then hid a toy in one well and covered it with cloth, hiding it from view. The infant was considered successful if they correctly retrieved the toy twice from well A and then once from well B after the researcher hid it.

"How babies perform in this task tells us about their development because it's a coordination of multiple skills," said Leigha MacNeill, "They have to remember where the ball was moved, which is working memory. even though it's out of sight, and they need to track objects moving in from one place to another.

The researchers also measured the infants' EEG at each visit. A cap with six electrodes was placed on the baby's head, with each electrode measuring the electrical activity in different regions of the brain. Readings were taken for two minutes while the infants focused on a spinning wheel.

After analyzing the data, the found that performance on the a-not-b task did indeed develop in bursts: with most of the infants, there was a lot of development in the first or last months, but there was a big spike between seven and eleven months. At the same time, the researchers found that EEG power grew at a steady pace throughout the seven months .

Because the researchers analyzed each baby's personal development, in addition to taking an average of all the babies together, MacNeill said the results help shed some light on what's happening in the brain when infants are learning new skills . "Infant behavior varies from baby to baby, so it's helpful to understand what is going on beneath the surface," MacNeill said.

The multi-method approach is helpful, because we can see both the infants' behavior and also what is going on in the brain. It gives us a better sense of where this variability comes from, and can help us see what's happening in the brain when the child is not getting better at the task when there is rapid development.