We are all time travelers. We travel into the past; vividly remembering yesterday, last week, and previous decades. We also travel to the future; planning the weekend, imagining next year, and daydreaming about retirement. Sometimes we intentionally remember the past and imagine the future. But frequently our minds wander unintentionally. Instead of focusing on what we are doing now, we relive our past glories and daydream about tomorrow.
The trick is to not get lost. When I find myself wandering through the yesterdays in my mind, how do I get back to the correct future – to now? Do I need a mad scientist with a souped-up DeLorean to get Back to the Future? When I’m flying along in my time traveling mental sports car, how do I know when to stop? How do I keep track of now? Getting home safely after time traveling is a critical job for memory. Memory both takes us into the past and brings us safely home. In addition, my memory of the past allows me to create a vision of the future. Memory provides the maps so we don’t get lost.
We can time travel without fear of getting lost because our memories are constantly updated by our most recent experiences. Each time I have a new event within a set of experiences, that new memory becomes the experience most strongly connected to that set of events. That new memory will become the easiest event to remember – a phenomenon known as the recency effect. For example, when I think of a class I’m teaching now, I remember most clearly and easily what happened in our most recent class session. Remembering that most recent session allows me to know what to do today in class. When I think about going out to dinner, I recall the most recent outing with my wife.
Not only are the recent experiences the strongest memories, but the previous memories get weaker and harder to recall with every new episode. I know when I am because my recent experiences are most clearly remembered. Class sessions before last week only vaguely enter my awareness when I think about the Cognitive Psychology class I am teaching this term. Of course, older memories aren’t lost, they simply become harder to recall. I most clearly remember my most recent night out with my wife, but I can also remember earlier dinners and dates. But remembering some of those earlier dinners requires extra work. I have to think about everything else that happened last month to provide my memory additional cues to remember our fun evening at Serious Pie in Seattle last month. I can discern now from the more remote past in my memories by how easily and clearly things come to mind when I think about sets of events.
Keeping now distinct from my plans, hopes, and dreams of the future works similarly. Imagining the future is a common human activity. I daydream possible futures by building on past experiences. But no matter how vivid my daydreams, they are ephemeral wisps compared to the world around me and compared to my recent memories. Marcia Johnson and her colleagues have often described this as a process of reality monitoring. In reality monitoring, we use the clarity of images and ideas to differentiate between what we’ve done and what we’ve only imagined doing. Did I give this lecture to my class or only think about giving this lecture?
Of course, the process of reality monitoring can break down – our imagining of something can appear so clear and complete as to appear like a memory. Then we can create false memories (see my earlier posts on creating false memories: Spilled Punch and False Memories, and Lies, Damned Lies, and Photographs). We all frequently suffer from wondering whether we did something or only thought about doing something.
People with Alzheimer’s disease and other forms of amnesia are often lost in time. They’ve gone on time traveling expeditions, but can’t find their way back to the present. They can’t find their way back to now, because their memories have not been updated by their most recent experiences.
Mental time travel seems particularly important in relationships. I want to revisit our beautiful past together and imagine our future. But I also have to keep track of the current status of our relationship. Were we fighting or were we planning a vacation? What were we doing the last time we were together? Losing track of the current status can be embarrassing or worse. Your partner may wonder why you keep bringing up the same conversation.
Memory is my mental time machine. I travel to the past in my memories and to the future by imagining possible events. Memory is also my mental GPS, keeping me located in the now by constantly updating my past. Using memory, I can wander the corridors of time and always come home to now.