A report on ABC news suggests that using fMRI brain imaging to detect lies is as simple as comparing two “pictures” of brain activity:
How do you tell which is the truthteller? It’s easy, the article claims:
Who needs Pinocchio’s nose to find a lie? The FMRI scan on the right detects a brain processing a false statement; the less colorful brain on the left corresponds to someone in the middle of a truthful statement.
According to the article,
When someone lies, the brain first stops itself from telling the truth, then generates the deception. When the brain is working hard at lying, more blood rushes to specific portions of the brain and that’s what can be detected on the machine.
Accurate lie detection, it seems, could be conducted by a monkey with an fMRI. Why aren’t the courts scrambling to adopt this new technology?
As several blogs have pointed out, things aren’t really that simple.
Unless you’re dead, an fMRI image never looks like the one on the left. An fMRI measures blood flow, and there’s always blood flowing through the brain, even during sleep. As the Neurocritic points out, if we are to believe these images, “the only activity in the truth-telling brain on the left seems to be located mostly outside the cerebral cortex.”
Reading between the lines of the ABC News article, I’m guessing that how the technology really works is by comparing two different fMRI images. You establish a baseline by asking the suspect to make true responses to questions like “Am I wearing a blue shirt?” or “Is it raining today?”
Then you move on to questions about the alleged crime (“Miss Scarlet, did you kill Professor Plum in the billiard room?”). It’s only by comparing the baseline scans with the scans taken during the questions about the crime that you can generate images like the ones depicted above. Each pixel on the image (or “voxel” in a 3D space) is generated by subtracting the value from one scan and another. In fact, virtually any fMRI image you ever see is the result of a similar subtraction process, usually between the “resting state” and some other state that is of interest to researchers.
But the brain process responses to questions about shirt color differently than questions about murder. So subtracting two MRI scans during responses to different questions, even when both responses are truthful, is never going to look like the image on the left. fMRI lie detection involves a lot more than just subtraction: the operator needs to know which areas of the brain are typically activated in a myriad of processes. The problem comes with the decision to filter those out so that clear “colorful” images can be created, making the business of lie detection seem simpler than it is.
Who’s to judge whether the fMRI operator made good decisions while analyzing the data? There are dozens of points where error or bias can be introduced. It’s no surprise, then, that No Lie MRI can claim only 90 percent accuracy.
I wonder if, in the messy real world rather than a controlled lab environment, they can even be that accurate.