Eyewitness psychology is a field within psychology that studies how people perceive, store, and recall memories of events they have witnessed. The subject is an application of memory psychology and is highly important within the justice system, particularly in police investigations and trials.
As early as the 1890s, the psychologist James Cattell examined people's memory ability by having students recount everyday events. In one of his experiments, participants were asked to estimate the weather on a particular day. The results showed that only 10% correctly remembered that it had been snowing, showing that people's memory of everyday events is often limited and imprecise.
Human memory
Research shows that inaccurate witness testimony is rarely due to people deliberately lying. Instead, errors often arise because memory is reconstructive, meaning it is influenced by attention, stress, prior experiences, and expectations. Eyewitness memory therefore does not function as an exact recording of reality, but as an active interpretation of what has been experienced.
If a person, for example, answers 32 of 40 questions and gets 24 of them right, the result can be analyzed in two ways. One can look at either the proportion of correct answers out of all questions (60%), or the proportion of correct answers out of the questions the person actually answered (75%). These two measures show different aspects of memory: how extensive the account is, and how accurate the information given actually is.
The difference between these measures shows that memory is not just about how much information a person can recall, but also about how reliable that information is. In forensic psychology, both aspects matter, since a witness may give many answers while still being uncertain, or give few but highly accurate details.
The divisions of memory
Human memory is often divided into short-term memory, working memory, and long-term memory. Short-term memory stores information for a very brief period, usually only a few seconds. It helps us temporarily remember things like a phone number right before we manage to write it down. Working memory is the part of memory that not only stores information temporarily but also processes it. When you calculate a number in your head or follow several instructions at once, you are using your working memory. Long-term memory stores information for a long time, from hours to an entire lifetime. This is where our knowledge, experiences, and personal memories are kept. For information to be transferred from short-term memory to long-term memory, processing is required. It is not only about how long something stays in our short-term memory, but also about how we work with the information. If we place it in a context and connect it to our previous experiences, or if we experience it as meaningful, the likelihood that it will be stored in long-term memory increases.
According to a common model, working memory consists of several subsystems that interact. One part functions as a central control system that directs attention and allocates resources between different tasks. Another part handles visual and spatial information, for example when we picture images or orient ourselves in an environment. A third part handles linguistic and sound-based information, for example when we repeat words in our inner speech.
Because working memory has limited capacity, it can be difficult to perform two tasks at the same time if they require the same type of processing. For example, it is often difficult to listen to a text and simultaneously write a coherent text of your own, since both tasks use linguistic resources. On the other hand, it can be easier to combine tasks that use different parts of working memory, for example listening to a lecture while drawing a simple picture.
Different types of long-term memory
Long-term memory is not a single, unified system either, but consists of several different types of memory that are stored and used in different ways.
Procedural memory concerns knowledge of how to perform actions. This can, for example, be cycling, swimming, or playing an instrument. These memories often become automatic after a lot of practice and then no longer require conscious effort.
Semantic memory consists of factual knowledge and general information about the world, for example that Stockholm is the capital of Sweden or that 2 + 2 is 4. This type of memory is independent of when or where the information was learned.
Episodic memory concerns personal experiences and events we ourselves have taken part in, for example a vacation trip or a specific situation in childhood. This type of memory is often particularly important in eyewitness psychology, since it is the one used when people recount events they have witnessed.
Meaningful memories
People find it easier to remember information they understand and can relate to previous knowledge. When information is experienced as meaningful, it becomes easier to store and recall, while information that feels unfamiliar or difficult to interpret often changes in memory. The psychologist Frederic Bartlett demonstrated this in a classic experiment in which participants retold a story to each other in several steps, similar to a game of telephone. In the cases where Bartlett used a story from another culture that contained elements unfamiliar to the participants, the story gradually changed as it was retold. Participants removed details that felt unfamiliar and altered parts of the story so that it became more comprehensible based on their own Western experiences.
The experiment showed that memory does not function like a camera that stores information exactly, but that people actively interpret and reshape memories. When we have to remember events that we cannot relate to as easily, things that are unfamiliar to us, our ability to remember becomes worse. This naturally affects witnesses but also those who are to judge in a trial. It can be difficult to remember things like complicated fraud schemes or how DNA analysis works, since the information is abstract and hard to relate to. Whereas it is easier to remember and relate to a witness vividly describing the defendant holding a gun.
