Effects of Post-event Information on Memory

Can information given to eyewitnesses after an event has taken place actually become part of their memory of that event?

To test how post-event information influences subject memory of an event, Elizabeth Loftus designed this ingenious study. First she had all subjects view a video tape of a car crash. Then one week later she asked the subjects a series of questions about what they saw in the video.

All subjects were asked the same questions except for one small difference, half were asked, "About how fast were the cars going when they hit each other?"

while the other half were asked, "About how fast were the cars going when they smashed into each other."

This slight difference in questions constitutes the independent variable, or antecedent conditions she manipulated.

After a second week all subjects were again asked the same questions, one of which was, "Did you see any broken glass?"

This is the dependent variable.

Almost twice as many subjects who had heard the word "smashed," as opposed to "hit," reported having seen broken glass. There was no broken glass in the original video!!!

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Loftus E. F. ,1979, Effects of Post-event Information on Memory. Eyewitness Testimony. Cambridge, MA: Havard University Press.