Ever put salt in your tea instead of sugar after a sleepless night?
In that groggy sleepy haze, you’re also more likely to sign a false confession, according to a study by American psychologists.
A study led by Steven Frenda from the New School of Social Research in New York found sleep-deprived subjects were almost five times more likely to admit to something they hadn’t done than their well-rested counterparts.
“This is the first direct evidence that sleep deprivation increases the likelihood that a person will falsely confess to wrongdoing that never occurred,” said study co-author and University of Michigan psychologist Kimberly Fenn.
But a couple of simple tests may pinpoint the people most likely to sign a false confession.
This is crucial, as false confessions are implicated in 15-25% of wrongful convictions, and previous studies show most occur following interrogations longer than 12 hours.
Yet it was revealed last year that the Central Intelligence Agnecy routinely used sleep deprivation for up to one week during detainee questioning – some of whom were lately found to be wrongfully held.
So Frenda and colleagues performed a simple experiment to see how a sleepless night affects the odds of admitting wrongdoing when innocent.
Some 88 subjects were given a battery of tests to complete on a computer in Fenn’s sleep laboratory.
During the tests, they were routinely told not to hit the “Escape” key as doing so would clear important study data.
That night, half the subjects slept for eight hours in the laboratory while the remainder were kept awake.
The following day, all subjects were shown a statement describing their time in the laboratory, which included the false statement that they had, at some point, compromised the study by pressing the Escape key.
The subjects were asked to read the statement then tick a box and type their name to confirm its accuracy.
Half the sleep-deprived subjects signed the statement the first time it was shown to them, compared to 18% of the rested subjects.
When the psychologists measured other factors, they found sleep-deprived subjects who scored highly on a cognitive impulsivity test were more likely to sign the false confession than those who scored low, as were those who reported being sleepier – regardless of being sleep-deprived or not.
The researchers suggest interrogators check these factors before obtaining a confession.
They admit their study does have a few limitations. For one, it doesn’t shed any light on sleep deprivation’s effect on true confessions – it may increase those rates too.
And the consequences of signing the false confession statement weren’t made clear to the study subjects. They may have assumed no repercussions, so signing their name wasn’t a big deal.
Regardless, the researchers propose that sleep deprivation “sets the stage for false confession by impairing complex decision making abilities – specifically, the ability to anticipate risks and consequences, inhibit behavioural impulses, and resist suggestive influences”, and recommend that all interrogations be filmed to allow judges, juries and attorneys to evaluate the conditions where confessions are extracted.
They reported their results in the Proceedings of the National Academy of Sciences.
Belinda Smith is a science and technology journalist in Melbourne, Australia.
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