Most of us don't have any memories from the first three to four years of our lives. And when we do try to think back to our earliest memories, it's often unclear whether they are the real thing or just recollections based on photos or stories told to us by others. The phenomenon (现象), known as "childhood amnesia", has been puzzling psychologists for more than a century—and we still don't fully understand it.
At first glance, it may seem that the reason we don't remember being babies is that babies don't have a fully developed memory. But babies as young as six months can form both short-term memories that last for minutes and long-term memories that last weeks. In one study, six-month-olds who learned how to press a button to operate a toy train remembered how to perform this action for two to three weeks after they had last seen the toy. Preschoolers can remember events that go years back.
Of course, memory capabilities at these ages are not adult-like. In fact, developmental changes in basic memory processes have been put forward as an explanation for childhood amnesia. These basic processes involve several brain regions and include forming, maintaining and then later retrieving (检索) the memory. For example, the hippocampus, thought to be responsible for forming memories, continues developing until the age of seven. The typical boundary for the offset of childhood amnesia—three and a half years—changes with age. Children and teenagers have earlier memories than adults do. This suggests that the problem may be less with forming memories than with maintaining them.
But this does not seem to be the whole story; language also plays a role. From the ages of one to six, children progress from the one-word stage of speaking to becoming fluent in their native language(s), so there are major changes in their verbal (言语的) ability that overlap with the childhood amnesia period. This includes using the past tense, and memory-related words such as "remember" and "forget".
It's true to some extent that a child's ability to verbalize about an event at the time that it happened predicts how well they remember it months or years later. One lab group conducted this work by interviewing young children brought to accident and emergency departments for common childhood injuries. Those over 26 months, who could verbalize about the event at the time, recalled (回忆起) it up to five years later, while those under 26 months, who could not talk about it, recalled little or nothing.
Even if we can't clearly remember specific events from when we were very young, their accumulation, however, leaves lasting tracks that influence our behavior. The first few years of life are forgettable and yet powerful in shaping the adults that we become.
