A child younger than three or four years old has more difficulty remembering things as he gets older. Some researchers have even claimed that young children do not form memories, but this is false. However, their memories may fade as they get older or older memories are sometimes replaced with newer memories. Some may not even remember simple things like their third or fourth birthday. Furthermore, other researchers think that this has to do with cognitive and linguistic abilities. According to psychology professor Carole Peterson: “this is not the case. Very young children can still remember past events.” Peterson also said, "As young children get older, their first memories tend to come later and later, but around age ten their memories crystallize." The researchers even carried out tests to check the children's memory. What they did was ask 140 children between the ages of 4 and 13 to describe their earliest memories, then asked them two years later. They had to estimate their age at the time and their parents had to confirm it. In doing so, they found that children aged 4 to 7 showed very little overlap between the memories they recalled first and those they recalled two years later. Peterson said, "Even when we repeated what they had told us two years earlier, many of the younger children told us it hadn't happened to them." ⅓ of children aged 10 to 13 described the same first memory during the second interview. More than half of the memories were recalled in the same way