How remembering can change a memory

Imagine disagreeing with a friend about which day a teacher introduced a new topic. You can picture the classroom and remember the explanation, but your friend insists it happened on Tuesday, not Monday. The vivid scene does not settle the date. The lesson and its place in the week are different details, and remembering one does not guarantee remembering both. You might agree about the explanation itself and still have little evidence about which day it was given.

Psychologists study these disagreements by giving people an experience whose details can be checked later: a short film, a list of objects or a sequence of words. Researchers can then change a question, introduce new information or compare accounts over time. Some errors come from forgetting. Others involve supplying a detail that was never there. The experiments help separate those possibilities. ¹²³⁴

The wording of a question can matter

In 1974, Elizabeth Loftus and John Palmer showed participants films of car accidents and asked them to estimate the vehicles' speed. A question using the verb smashed produced higher estimates than questions using milder verbs such as hit. The films had not changed; the wording used afterwards had. ¹ In a second experiment, participants returned a week later and were asked about broken glass. There had been none in the film. Those who had received the smashed question were more likely to report seeing it. The wording had affected a later report about the event. ¹

The experimenters could compare the reports with the films, but could not directly observe the participants’ memories. Someone might infer what the questioner expects, make a different judgement or confuse a detail supplied afterwards with something they saw. Those possibilities matter when interpreting how the wording produced the effect. ¹

Remembering the meaning can introduce a detail

In 1995, Henry Roediger and Kathleen McDermott asked participants to learn lists of related words. The lists omitted a strongly associated word: bed, rest and awake could appear without sleep. Participants often recalled the absent word, sometimes recognising it later with considerable confidence. ²

These lists make the distinction between a word and its meaning unusually clear. The words all point towards a common idea. That idea may become familiar enough to be mistaken for an item that was actually presented. An association that helps someone understand the list can also contribute to a specific error about its contents. ²

Because each list was scripted, researchers could check every response against an exact record. That is harder when studying an everyday conversation or journey. The controlled task makes the error clear, while leaving open how often similar mistakes occur outside the experiment. ²

When an old memory meets new information

Almut Hupbach and colleagues tested memory updating in 2007. Students learned a set of objects, then another set the following day. On the third day, some incorrectly included newer objects when recalling the original set. This mixing depended on whether they had received a reminder of the first learning session before learning the second set. ³

The delay mattered. In another experiment, the effect was not found when the original set was tested immediately after the second learning session. The researchers interpreted the delayed intrusion of new objects as evidence consistent with reconsolidation: a reactivated memory undergoing another period of stabilisation. ³ The reminder, new learning and delay belonged to a particular experimental arrangement. Reconsolidation is an account of the observed pattern; these behavioural measurements alone do not identify its molecular cause or establish that every act of recall changes a memory. ³

A clear memory can still change

Jennifer Talarico and David Rubin studied memories outside a word-list experiment. On 12 September 2001, 54 Duke University students recorded how they had first heard about the previous day's terrorist attacks. They also recorded a recent everyday event. The students were questioned again after one of several delays, extending to 32 weeks. ⁴

Accounts of both kinds of event became less consistent over time. Yet the students' belief in the accuracy and vividness of the September 11 memories stayed comparatively high. The special feeling attached to a consequential event did not keep every reported detail stable. ⁴

The earlier written accounts gave the researchers a baseline for measuring consistency. A later answer that differed showed that at least one account was inaccurate. Matching answers, however, would not independently verify the original experience. The method could track changes without establishing the truth of every remembered detail. ⁴

Checking a particular detail

In the classroom disagreement, the timetable or a dated set of notes would help with the date. Remembering the explanation would help with the topic. A dated worksheet might even show that the teacher introduced an idea in one lesson and returned to it in another. Looking for that separate record is more useful than deciding that the person with the clearest mental picture must be right. It leaves room for an ordinary outcome: both people remember something real, but they are placing it in different lessons or treating different moments as the beginning of the topic.