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Some may beat “guilt-detection” tests by suppressing memories

May 29, 2013
Courtesy of the University of Cambridge
and World Science staff

New “guilt de­tec­tion” tests de­signed to check brain ac­ti­vity for signs of guilty mem­o­ries are be­ing used in sev­er­al coun­tries—but they’re not fool­proof, a study sug­gests.

Some test sub­jects man­age to es­cape de­tec­tion by sup­press­ing the in­crim­i­nat­ing mem­o­ries, ac­cord­ing to psy­chol­o­gists.

The Big Brother-like tests have gained cur­ren­cy in law en­force­ment agen­cies in sev­er­al coun­tries, in­clud­ing Ja­pan and In­dia. They’re al­so com­mer­cially avail­a­ble in the Un­ited States. The tests are based on the log­ic that crim­i­nals will have spe­cif­ic mem­o­ries of their crime stored in their brain.

Once pre­sented with re­minders of their crime in a guilt de­tec­tion test, it’s as­sumed that a sub­jec­t’s brain will au­to­mat­ic­ally and un­con­trol­lably rec­og­nize these de­tails, caus­ing the sys­tem to register the “guil­ty” re­sponse.

But re­search by psy­chol­o­gists at the uni­vers­i­ties of Kent, Mag­de­burg and Cam­bridge and the Med­i­cal Re­search Coun­cil in the U.K. found that some peo­ple can de­lib­er­ately sup­press un­wanted mem­o­ries, abol­ish­ing the “guilt­y” trace.

In ex­pe­ri­ments, the re­search­ers asked peo­ple to car­ry out a de­tailed, mock bur­gla­ry in a com­put­er game. They lat­er tested the par­ti­ci­pants by meas­ur­ing their elec­tri­cal brain ac­ti­vity to de­tect “guilt” or “in­no­cence.”

When they asked par­ti­ci­pants to sup­press their “crime” mem­o­ries, on av­er­age, about 18 per­cent of par­ti­ci­pants man­aged to re­duce their brain’s re­sponse and ap­pear in­no­cent, the sci­en­tists re­ported. The find­ings are to ap­pear in the Sep­tem­ber is­sue of the jour­nal Biolog­ical Psy­chol­o­gy and are in the ad­vance on­line edi­tion.

“Us­ing these types of tests to say that some­one is in­no­cent of a crime is not val­id be­cause it could just be the case that the sus­pect has man­aged to hide their crime mem­o­ries,” said Zara Bergstrom of the Uni­vers­ity of Kent, the prin­ci­pal in­ves­ti­ga­tor.

“Not eve­ry­one was able to sup­press their mem­o­ries of the crime well enough to beat the sys­tem. Clear­ly, more re­search is needed to iden­ti­fy why some peo­ple were much more ef­fec­tive than oth­ers,” added Mi­chael An­der­son, a sen­ior sci­ent­ist at the Med­i­cal Re­search Coun­cil Cog­ni­tion and Brain Sci­ences Un­it in Cam­bridge, U.K. His group is try­ing to un­der­stand such in­di­vid­ual dif­fer­ences with brain im­ag­ing.


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New “guilt detection” tests designed to check brain activity for signs of guilty memories are being used in several countries—but they’re not foolproof, a study suggests. Some test subjects manage to escape detection by suppressing the incriminating memories, according to psychologists. The Big Brother-like tests have gained currency in law enforcement agencies in several countries, including Japan and India. They’re also commercially available in the United States. The tests are based on the logic that criminals will have specific memories of their crime stored in their brain. Once presented with reminders of their crime in a guilt detection test, it’s assumed that a subject’s brain will automatically and uncontrollably recognize these details, with the test recording the brain’s “guilty” response. But research by psychologists at the universities of Kent, Magdeburg and Cambridge and the Medical Research Council in the U.K. found that some people can deliberately suppress unwanted memories, abolishing the “guilty” trace. In experiments, the researchers asked people to carry out a detailed, mock burglary in a computer game. They later tested the participants by measuring their electrical brain activity to detect “guilt” or “innocence.” When they asked participants to suppress their “crime” memories, on average, about 18 percent of participants managed to reduce their brain’s response and appear innocent, the scientists reported. The findings are to appear in the September issue of the journal Biological Psychology and are in the advance online edition. “Using these types of tests to say that someone is innocent of a crime is not valid because it could just be the case that the suspect has managed to hide their crime memories,” said Zara Bergstrom of the University of Kent, the principal investigator. “Not everyone was able to suppress their memories of the crime well enough to beat the system. Clearly, more research is needed to identify why some people were much more effective than others,” added Michael Anderson, a senior scientist at the Medical Research Council Cognition and Brain Sciences Unit in Cambridge, U.K. His group is trying to understand such individual differences with brain imaging.