Your memory of events is distorted within seconds

Your memory automatically fills in the blanks in unfolding events

Memory isn't etched in neural stone. It's a creative process, sketched in sand. In one of the most dramatic demonstrations of this yet, Brent Strickland and Frank Keil have shown how people's memory for a video clip was distorted within seconds, to form a coherent episode "package". They said their finding provided evidence that the mind uses "sophisticated compression routines ... for efficiently packaging previous events as they are being sent to memory."

Fifty-eight uni students watched three types of 30-second video clip, each featuring a person kicking, throwing, putting or hitting a ball or shuttlecock. All videos were silent. One type of video ended with the consequences of the athletic action implied in the clip - for example, a football flying off into the distance. Another type lacked that final scene and ended instead with an irrelevant shot, for example of a linesman jogging down the line. The final video type was scrambled, with events unfolding in a jumbled order. Crucially, regardless of the video type, sometimes the moment of contact - for example, the kicker actually striking the ball - was shown and sometimes it wasn't.

After watching each video clip, the participants were shown a series of stills and asked to say if each one had or hadn't featured in the video they'd just watched. Here's the main finding. Participants who watched the video type that climaxed with the ball (or shuttlecock etc) flying off into the distance were prone to saying they'd seen the causal moment of contact in the video, even when that particular image had in fact been missing.

In other words, because seeing the ball fly off implied that the kicker (or other protagonist) had struck the ball, the participants tended to invent a memory for having seen that causal action happen, even when they hadn't. This memory distortion happened within seconds, sometimes as soon as a second after the relevant part of the video had been seen.

This memory invention didn't happen for the videos that had an irrelevant ending, or that were scrambled. So memory invention was specifically triggered by observing a consequence (e.g. a ball flying off into the distance) that implied an earlier causal action had happened and had been seen. In this case, the participants appeared to have "filled in" the missing moment of contact from the video, thus creating a causally coherent episode package for their memories. A similar level of memory invention didn't occur for other missing screen shots that had nothing to do with the implied causal action in the clip.

A second study replicated these memory distortion effects with 58 more participants and with new contexts involving kicking, throwing and bowling.

The researchers said their findings have obvious implications for crime scene witnesses. Imagine a witness sees a man wielding a gun, and imagine seconds later they also see a person nearby falling from a gunshot wound - these new results show how easily the mind of the witness could invent a memory of having seen the moment the trigger was actually pulled. "In some circumstances," the researchers said, "conceptual packaging can induce the perceiver to insert unseen information in order to fulfil structural requirements. This was the case in the present study."

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Strickland, B., and Keil, F. (2011). Event completion: Event based inferences distort memory in a matter of seconds. Cognition, 121 (3), 409-415 DOI: 10.1016/j.cognition.2011.04.007


Post written by Christian Jarrett for the BPS Research Digest.