For many, it tends to strike us as odd when we experience the same event with a friend or family member, but result in having completely different memories from the experience. So, why is it that some people can recall the same event so differently? We all know memory isn’t perfect, and most memory differences are relatively small or insignificant, but sometimes they can have serious consequences.
Imagine if you and a friend both witnessed a crime. What factors lead to memory differences and whom should be trusted to be the best source of information? According to new research, there are three important aspects to memory: encoding, storage, and retrieval.
Memory encoding starts with perception — the organisation and interpretation of sensory information from the environment. The salience of sensory information (for example, how bright a light is or loud a sound) is important – but perception does not rely on salience alone.
In saying that, perception is strongly affected by what we have experienced in the past and our expectations of what we might experience in the future, and how it’s compared to the individual situation. These effects are called top-down processes, and have a big impact on whether we successfully encode a memory.
One of the most important top down processes is attention, which is basically our ability to focus selectively on parts of the world, to the exclusion of other parts, and everything around us. While certain visual items can be perceived or encoded into memory with little or possibly no attention, attending to items is hugely beneficial for perception and memory.
Age also contributes to differences in memory, because our ability to encode the context of memories diminishes as we get older. Context is an important feature of memory. Studies show that if we attend to both an item and its context, we remember the item better than if we attend to the item alone. For example, we are more inclined to encode the location of our car keys if we focus on both the keys and how we have placed them in a room, rather than just focusing on the keys alone.
So how exactly do people store memories? Memories are first encoded into a temporary memory store called short-term memory. Short-term memories decay quickly and only have a capacity of three or four bits at a time. But we can group larger bits of information into manageable chunks to fit into memory. Information in short-term memory is held in a highly accessible state so we can bind features together. Techniques such as verbal rehearsal allows us to consolidate our short-term memories into long-term memories. Long-term memory has an enormous capacity. We can remember at least 10,000 pictures, according to a study from the 1970s.
The study also discovered that long-term memory can also be enhanced by drinking caffeine immediately after learning something. The study used caffeine tablets to carefully control dosage, but this builds on growing evidence for the benefits of moderate coffee consumption.
The complexity of memory retrieval is exemplified by something called “tip-of-the-tongue states” which is the common and frustrating experience that individuals hold something in long-term memory, but generally cannot retrieve it right away. The emergence of brain imaging has meant we have identified many brain areas that are important for memory retrieval, but the full picture of how retrieval works remains mysterious.
However, retrieval is also affected by the outside world. The study also instructed people to view films of car accidents and then asked them to judge the speed the cars were moving. Interestingly enough, if the participants were asked how fast the cars were moving when they “crashed” into each other they judged the cars as moving faster than if the words “contacted” or “hit” were used.