Baby talk is more than just bonding: chatting with your infant spurs important brain development that sets the stage for lifelong learning, researchers said. And while high-pitched, sing-song tones may capture your baby's attention, the best way for them to learn is to be spoken to like adults. At least when it comes to vocabulary and sentence structure. "It's not just how much speech you get, but the kind of speech you get," Erika Hoff, a psychologist at Florida Atlantic University in the US, said on Thursday. "Speech needs to be rich and complex." Talking to babies is so important that researchers say it is a major reason why children from disadvantaged backgrounds perform poorly in school. By the time they reach the age of five, the children of low-income, poorly educated parents typically score two years behind their privileged peers on standardised language tests. These differences can also be measured in the brain, said Columbia University neurologist Kimberly Noble. The human brain experiences incredible growth in its early years. By the age of three, it has formed 1,000 trillion neural connections - the links between cells that help the brain do everything from picking up a stick to remembering song lyrics. "A child's experiences really come into play to determine whether those connections strengthen or are dropped or pruned," Noble said. Noble and her colleagues compared children from poorer and richer backgrounds. While they found differences in the cognitive systems that support social skills and memory, the largest disparities were in brain structures for language development. Stanford University psychologist Anne Fernald has found that the language gap can be measured as early as 18 months. By a child's second birthday that gap is already six months wide. Fernald and her colleagues made recordings of what a group of low-income, Spanish-speaking children heard all day. They found that infants did not gain much from simply overhearing their parents and caregivers talk - the real learning came from being spoken to directly. It was crucial to develop "culturally sensitive interventions" to teach low-income parents to talk to their children, Fernald said. "There's a wide range of views about whether it's even appropriate to talk to a child - in some cultures it is not," Fernald said.