Witnessing an event is an extremely complex process beginning with the acquisition of the observation, followed by the retention or storage phase, and finally the retrieval phase where the recollection is described verbally.
The human memory has been studied for well over 100 years by researchers around the world. As far back as 1902 in Berlin a staged event in a classroom was studied for the accuracy of the witnesses’ retrieval of information. The students in the classroom were broken into groups and asked to write a report on their observations of a staged event—some immediately, some a day or a week later. The study revealed that the smallest number of mistakes was 26 percent erroneous statements, and the largest number of errors was 80 percent. The more emotional part of the fictitious event, where a gun was drawn and a shot fired, averaged 15 percent more errors than the first half. In addition, statements made by the participants were inaccurately attributed or simply made up. Plus, some of the major points of the staged event were completely eliminated by a number of witnesses.
This study from 1902 has been replicated in a variety of different ways and fashions over the subsequent years, but each concluded that the human memory was far from accurate. The memories are described by most researchers as falling into three stages: 1) the acquisition stage, 2) the retention stage, and 3) the retrieval stage.
Acquisition Stage
When a witness first observes an event, only some of the details are observed and stored as part of the subsequent memory. The witness has to determine based on their observations which details are worth remembering based on where their eyes were focused and which details might be important later in deciding what to do.
Retention Stage
The retention stage is the time between the observation of the event and recalling the details observed. The retention period could be a matter of moments or a much longer period of time depending on the witness’s need to talk about the actions. The retention stage of the observation can be affected when the witness is privy to new information. This new information could be provided by other witnesses to the event, media reporting, the interviewer’s questioning the witness, or a variety of other sources.
Retrieval Stage
This part of the memory can be one of the more difficult components since the memory is not stored in one particular location in the brain but rather spread throughout the brain and linked in many different ways using our senses. The accuracy of the witness’s information retrieval can be affected in all three of these areas. If the witness failed to observe a particular detail of the event, there is no memory of it, but questions posed may infer information that taints the retention. The other issue is the words used by the witness to describe the situation and the interviewer’s assumptions of what they mean.
Time
Let’s consider the development of a memory beginning with the acquisition phase and the things that can affect the retention and retrieval of details. First, the more amount of time the witness has to make the observation, the more information they will likely be able to retrieve accurately. In one study conducted in 1971 by K. R. Laughery, participants were asked to look at slides of a human face for either 2.5 seconds or eight seconds each. After eight minutes, the participants viewed 150 projected slides of human faces and were asked to score whether these were the four faces they had seen. The research supported the idea that a greater amount of exposure time will lead to greater accuracy. Those viewing the slides for eight seconds achieved 58 percent accuracy, while for those viewing the slides for 2.5 seconds, the accuracy rate dropped to 47 percent. Most of the participants said that they focused on the general structure of the face, the eyes, and nose in making their decisions, while very few focused on the hair or ears in making their judgments.
Frequency
Many research studies have confirmed that something experienced many times is going to be recalled much better than something observed only once. Clearly, criminal events are very short in duration and often unexpected, so the accuracy of an observation is likely to diminish. However, seeing a person day after day entering a particular door, the witness would very likely have a much more accurate description of the individual.
Relevant Details
In every observation that we make, we tend to focus on only the most relevant or memorable details of the situation. Most observers will focus their observation on the things that captured their attention. As we might expect, these would be the most unusual or interesting parts of the event that would be much like a TV show and capture our attention. The opposite side is also true that we would less likely remember things that are uninteresting or commonplace during an observation.
The types of details that are important to be accurately retrieved in certain cases can be extremely problematic. For example, estimations of distance, time, and speed are especially difficult for witnesses to accurately estimate. In one of the earliest studies in this area (Marshall 1966/1969), participants were to estimate the speed of a vehicle. They knew in advance they would be asked to judge the speed, yet the estimates ranged from ten to fifty miles per hour, while the car was actually traveling at just twelve miles per hour.
Estimates of time are also difficult, but people generally overestimate the amount of time an event took rather than underestimating it. One hundred forty-one witnesses to a staged classroom event viewed a distraught student attacking a professor. The event, which was videotaped for comparison to the witness accounts, showed that the attack lasted thirty-four seconds. When questioned about the duration of the attack, the witnesses’ response averaged eighty-one seconds, almost three times longer than it took (Buckhout 1977/1975). Other studies confirmed this bias toward a longer estimation. Participants watched a forty-two second film and on average estimated that the film was a minute and a half (Marshall 1966). When there is stress involved in the observation, the witnesses are even more likely to overestimate time frames. While witnesses can also make errors in descriptions including heights and weights, they are not always like the over estimations of time frames.
Stress
Again, not surprisingly, adding stress to the observation of an event makes the ability to recall the situation much more difficult. For the interviewer, this means that the witness’s report should be treated cautiously because of the emotional situation observed. The level of stress may have increased the observer’s notice of the event, or it may have distracted them as they focused on escape or what they needed to do next. This is evident in the necessity of training in highly stressful situations so that the actions of a first responder are instinctual rather than having to be thought out. Reportedly during the battle of Gettysburg during the Civil War, some soldiers loaded the rifles repeatedly without ever firing a shot during the stress of battle.
Expectations
Witness observation can also be tainted because of their expectations surrounding an event. Knowing that your mail is delivered by a man each day may in fact taint your observation of a female letter carrier doing the job. In many situations, our memories may be deceived because we see and hear what we expect to hear in a common situation.
Our expectations also may have a cultural basis that alters our observations to meet our particular biases. These expectations may also be based on our past experiences. For example, we might see two people walking but only have a clear view of one whom we recognize as a friend. These two friends are almost always together, so our expectation might be to assign the second person (whom we couldn’t view clearly) as the other friend.
Personal prejudices can also play a role in a witness’s observations. When a person holds certain beliefs or stereotypes a person or group, the tone of an encounter can change dramatically and is often untrue. One has only to look at liberal or conservative reporting on a political event to see how the reporter can taint the event one way or the other. They might comment on how the conversation was portrayed, including tone of voice, delivery, or sequence, choosing clips that support their position.
Certainly knowing an event is going to occur prepares the observer for the observation. Interestingly, research has found that people are better able to describe a face when asked to consider it in terms of personality, rather than simply visual observation of the hair, eyes, nose, or other facial features.
In our next column we will consider the retention and retrieval stages of a witness’s memory. The important thing for the interviewer to remember is that the estimation of time is generally an overestimation while speed and distance are also difficult for a witness to accurately estimate. An observation made under stress can also lead to less detail from the witness.