In the not-so-distant past, Timehop made social media nostalgia mainstream.

It was one of the first popular social media features to give us a deliberate glimpse into our personal past by digging up photos from our online libraries. The photos were from years past, of events that presumably carried some significance, and the app made them easy for us to share with our friends. Facebook liked the idea so much that in 2015 it decided to roll the feature out universally on Facebook, calling it On this day.

Facebook has even taken it upon itself to appropriate the very term ‘memory’, classifying things as ‘memories’ only if they were posted on its site. It seems to be not-so-subtly implying that if something wasn’t posted on Facebook it may as well have not happened at all.

The feature helps us remember critical life events such as how many people liked our narcissistic social media indulgences and on what date we made the life-changing decision to friend someone.

But is Facebook appropriating more than just our pictures and comments, and instead actively reshaping what we remember in real life?

Helping Facebook learn

Make no mistake, Facebook works tirelessly to steer what we see on its website.

One of the many computer algorithms Facebook uses to optimize what we see online is the ‘memories’ algorithm, which presumably tries to present us with pictures from our past that we are most likely to share with others. As such, we help Facebook learn by engaging with things we like - and the more we like and share something, the more of it we see.

The problem is that algorithms have no empathy.

Algorithms don’t care that you may not want to see photos of your late cat, or of co-workers from a job you recently lost. You may soon be able to prevent Facebook from showing you photos of your ex, helping you to get over a breakup, but most other bad memories remain potential candidates for your intrusive On this day updates.

Some have adeptly said that not every memory needs to be rehashed and that we can do with less “inadvertent algorithmic cruelty”. Facebook has been known to make mistakes and has even officially apologised in the past for showing users grossly inappropriate memories, which were selected and displayed via their ‘memory’ algorithms.

As a memory researcher who is interested in how our memories can go really wrong, this makes me wonder whether this reminiscing as the result of apathetic social media algorithms is good or bad for our memories.

Helping us forget

Ok, so there are two sides to this.

The first side is that remembering specific life events is going to enhance memories for those specific events. In the scientific literature this is known as the “testing effect” or “retrieval practice”, which means that simply recalling information enhances our memory of it.

It is such a strong effect that simply remembering something is known to produce better retention of information than studying the same information for the same amount of time. This suggests that ten minutes of reminiscing may be better for your memory than ten minutes of studying.

BUT, by having intrusive Facebook notifications constantly reminding you of certain memories you also have the potential to severely distort your reality.

You see, on the other side of the argument we have the science demonstrating “retrieval induced forgetting”. This means that every time we retrieve a memory, the memory traces in the brain that form that memory become pliable. In other words, every time we remember something, the network of cells that make up that memory becomes active, and that network can easily change.

For example, say you are reminded on Facebook of a vacation you took two years ago. The prompt will most likely be a single photo of the event with some caption, like #WhatHappensInVegas, or something else that may now seen cringe-worthy.

Science says that as you remember the particular moment in which the photo was taken, you are likely forgetting related and unmentioned information. Forgetting related information like what the pool at your hotel looked like, or that you went to a show while you were there.

Mind you, it’s not just Facebook that can have this memory-altering effect. Rehashing memories in any situation has the potential to distort them. What is different about Facebook is that the prompts are being selected from your online persona so they already represent a distorted, social-media appropriate, version of your life.

This means that Facebook memory prompts give you double-distortion - distorting the memory in your brain with a previously distorted memory from on your social media.

Your reality or Facebook’s reality?

By having Facebook choose which events are presented as the most meaningful in our lives, it is potentially culling the memories the algorithm ignores. Simultaneously it is reinforcing the memories it has chosen, potentially making some memories seem more meaningful and memorable than they originally were.

Both of these are problematic processes that can distort our personal reality. We may be helping Facebook learn to optimize its features, but the relationship is not symbiotic. Facebook’s nostalgia features are messing with our memories.

To prevent this from happening we could go on a Facebook hiatus, or turn On this day notifications off entirely. But, in reality, this is one of those features that many of us may be unable to completely avoid. We may choose to shut off our notifications, but our friends and families will likely continue to use them

So, be cautious when using social media nostalgia features. Seemingly small memory prompts can have important implications for our personal memories.

This post is part of a series of articles called “Memory Mondays”, which focus on debunking common misconceptions and beliefs about how our memory works.

Dr. Julia Shaw works at London South Bank University in the department of Law and Social Sciences. She is a senior lecturer, researcher, and author of The Memory Illusion: Why you may not be who you think you are, to be published in 2016 by Penguin Random House.