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May 29, 2013

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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.