Memories of past whereabouts are frequently faulty

MELBOURNE, Australia — “Where were you last Thursday around 7:30 PM?” Variations of that question are unavoidable in courtroom and police dramas, and for good reason. Whenever the authorities suspect anyone of a crime, law enforcement wants to know if they have a credible alibi for the date and time of the offense. Unfortunately, a new study finds peoples’ recollections of their past whereabouts are incorrect quite often.

Australian researchers tracked the locations of 51 individuals who had volunteered for the project for a total of one month. Incredibly, when study authors asked participants to remember their movements from the past month, their recollections were wrong roughly 36 percent of the time.

“This is the first study to examine memory for where an event happened,” says lead author Simon J. Dennis, director of the Complex Human Data Hub at the University of Melbourne’s School of Psychological Sciences, in a press release. “We were able to use experience-sampling methods to actually examine people’s memories and analyze what is affecting memory error in their everyday life.”

Researchers fitted each participant’s smartphone with a tracking app that constantly kept note of both locations and surroundings via GPS. Additionally, every 10 minutes the tracking app recorded nearby sounds from the surrounding environment. For the sake of privacy, participants had the option to turn off the app or delete certain movements if they chose to do so.

People most often mix up when similar events occur

After a full month, volunteers completed a memory test consisting of various dates and times from the prior 30 days. Then, they were asked to select one of four markers on Google Maps displaying where they had been at that exact time.

Generally, participants tended to mix up their days across weeks. However, some even confused full weeks and specific hours across days as well. The poorest recollections occurred when one event became entwined with similar memories. For instance, one individual correctly remembered stopping to put gas in their car at a specific gas station chain, but mixed up the location.

Volunteers also frequently had false memories while recalling multiple places they had visited in a short period, such as an evening of bar-hopping. Although not as common, some participants also misremembered events involving similar sounds or movement patterns, such as walking through their local town on different days while listening to their favorite tunes.

“This has implications for alibi generation, as jurors tend to assume that a suspect who is wrong is lying,” Dennis concludes. “These results can alert investigators to the questions they should ask in order to catch the memory errors that suspects are likely to make.”

The study appears in the journal Psychological Science.