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The storage and processing of information inside the human memory is a process that is as fascinating as it is complex. The available space for memories is not infinite and it would be rapidly depleted if every detail of every single event in one’s life would be stored. For this reason, human memory focuses on just a few elements, neglecting the majority of information.
Being fallible, it is possible to deceive the human brain, implanting false memories, using the effect of suggestibility. This phenomenon is a cognitive bias that leads to the development of mistaken memories based on information that is presented at a later time. To study this effect, Stephen Lindsay and Marcia Johnson, respectively from Williams College and Princeton University, have conducted a study to investigate what were the elements involved in this process.
In a typical study on the effect of suggestibility on memory, a series of slide depicting a scene is presented to the participants to the experiment, followed by misleading indications about the picture shown. When their memory is tested, the subjects that had received such indications claimed to remember things that they actually had never seen.
Initially, it was believed that new information deleted older memories, as if these were “overwritten” by more recent events. But research has proved the opposite, in other words the coexistence of both memories.
Following this discovery, there were two major hypotheses for the explanation of this phenomenon, to which Lindsay and Johnson proposed a third:
- Accessibility. The subjects’ ability to remember the original information is impaired by the fact that recalling the most recent memory, in other words the suggestion, the wrong information, is faster and easier. As a consequence, the latter is more accessible than the former.
- Nonretention. The reason the participants claimed to remember an element they had never seen is the fact that, in actuality, the original information was not stored at all. Thus, there is no true suggestibility effect, but it is a memory that is born in that moment, without modifying previous memories.
- Source monitoring. This is the hypothesis proposed by the two researchers. The error at the base of the suggestibility effect is to be found in the confusion regarding the source that provided the information. In other words, the subjects unconsciously mistake in attributing the origin of a certain memory, claiming to have seen a precise detail in an image, while this information comes from a text provided by the researchers or from their words.
And, as confirmed by other studies, the more the circumstances are similar, the more likely it is to confuse the source: both the original information and the suggestion pertain to the same subject, in other words the elements to remember in an image, they are both presented in a short interval of time, in the same context, and often by the same researcher. The study of Johnson and Lindsay aimed thus at studying if different sources produced different suggestibility effects.
In the first phase of the test, the participants analyzed for twenty seconds the same complex office scene. Later, all the subjects read a detailed narrative description of the scene. Half of the participants, the control group, read a detailed description, while the rest, the group subjected to the suggestibility effect, read a text that contained misleading information. To conclude, they answered to two questionnaires: a recognition test about the elements present in the image (yes/no) and a source monitoring test (in which it was asked if the object was present only in the image, the text, in both or in neither of them).
In the recognition test, the group that had read the description with misleading information claimed to remember objects that they actually had never seen more than double the time than the control group (on average, 5.52 remembered objects vs. 2.67).
Conversely, the performances of both groups were almost identical in the source monitoring test. Obviously, the participants’ memory was not perfect, but their error rate was identical.
This experiment proved that the suggestibility effect can be reduced or eliminated, if the participants were asked to decide the source of the memory, rather than investigating if a certain element was present in the image or not.
In the yes/no test, the researchers suggest, the subjects answer based on the degree of familiarity of a certain element inside the scene. For example, if the scene is the interior of an office, one could remember a stapler being present, even if this was actually not depicted in the image.
Conversely, in the source monitoring test, the subject answer based on the information that their memory associates more with text or the image, limiting the suggestibility effect.
The results of this study were revealed to be extremely important with regard to the forensic witness field. Already in 1977, a study revealed that witnesses that have to carry out the recognition of the responsible of a certain crime are highly influenced by the mugshots they are shown previously. Therefore neglecting additional factors that they may have noticed, such as height and physique, and choosing the person that makes them remember more one of the faces they have previously observed.
Thus, the suggestibility effect is an example of a bias that can lead to catastrophic consequences, if it is not taken into consideration from the authorities that have the duty to protect the peace of the society one lives in.
- Lindsay, D. S., & Johnson, M. K. (1989). The eyewitness suggestibility effect and memory for source. Memory & cognition, 17(3), 349–358. https://doi.org/10.3758/bf03198473
- Loftus, E. F., & Loftus, G. R. (1980). On the permanence of stored information in the human brain. American Psychologist, 35(5), 409–420. https://doi.org/10.1037/0003-066X.35.5.409
- Brown, E., Deffenbacher, K., & Sturgill, W. (1977). Memory for faces and the circumstances of encounter. Journal of Applied Psychology, 62(3), 311–318. https://doi.org/10.1037/0021-9010.62.3.311