The earliest memory that I’m nearly certain is genuine is from when I was about four years old. I’m in the living room of my childhood friend who lived across the street from me, watching movers carry furniture and boxes from my family’s house into a large moving truck. I don’t remember where my friend was at the time or how I was feeling. It’s a simple memory, but it’s still remarkably vivid over twenty years later.
But I have a few memories that are from when I was even younger that I’m not certain are actually my own. Upon reflection, I’m pretty sure most of them were “implanted” later from home movies, photographs, or family stories, and I internalized those experiences as my own. I’m not alone: According to new research published in Psychological Science, around 40 percent of first memories are likely fictional.
These results were derived from a survey of 6,641 people in the UK, which found that nearly 2,560 respondents (38.6 percent) claimed to have memories from when they were two years old or younger, and almost 900 of those memories were from when the respondents were one or younger. The respondents were told they should be certain the memory was genuine and not based on a photograph or anything other than direct experience.
There’s just one problem: Humans don’t recall memories from when they were younger than 3.5 years old on average. For the study authors, so many people reporting vivid memories from their first two years of life strained credulity.
"Crucially, the person remembering them doesn't know this is fictional,” Martin Conway, the director of the Center for Memory and Law at the University of London said in a statement. “This is partly due to the fact that the systems that allow us to remember things are very complex, and it's not until we're five or six that we form adult-like memories due to the way that the brain develops and due to our maturing understanding of the world."
Analysis of the survey respondents’ language and descriptive details shed some light on why so many people seem to have fictional first memories. According to the researchers, these fictional memories are probably cobbled together from scraps of early experience—such as a particular feeling toward a family member, a favorite toy, and so on—and are combined with knowledge about their childhood that is learned later.
One particular type of fictional memory that was reported by many respondents had to do with their baby stroller or pram.
“For this person, this type of memory could have resulted from someone saying something like 'mother had a large green pram',” said Conway. “The person then imagines what it would have looked like. Over time these fragments become a memory and often the person will start to add things in such as a string of toys along the top.” Over time, these mental fragments are called to mind as an adult and experienced as “memories,” Conway explained.
Try thinking back as far as your memory allows. If you have a memory that occurred before you were three and includes a lot of details, there’s a pretty good chance it’s just a story you’ve told yourself as you’ve gotten older.
This article originally appeared on Motherboard.