We
don’t have a mind-reading machine yet, but that’s not to say we don’t have the
technology to create one.
The technique of functional MRI (fMRI), which measure
changes in localized brain activity over time, can now be used to infer
information regarding who we are thinking about, what we have seen and the
memories we are recalling. As the technology for inferring thought from brain
activity continues to improve, the legal questions regarding its potential
application in criminal and civil trials are gaining greater attention.
Last year, a Maryland man on trial for murdering his
roommate tried to introduce results from an fMRI-based lie detection test to
bolster his claim that the death was a suicide. The court ruled the test
results inadmissible, noting that the “fMRI
lie detection method of testing is not yet accepted in the scientific
community." In a decision last year to exclude fMRI lie detection test
results submitted by a defendant in a different case, the Sixth Circuit was
even more skeptical, writing that “there are concerns with not only whether
fMRI lie detection of ‘real lies’ has been tested but whether it can be
tested."
So far, concerns regarding reliability have kept
thought-inferring brain measurements out of U.S. (but not foreign) courtrooms.
But is technology the only barrier? Or, if more mature, reliable brain scanning
methods for detecting truthfulness and reading thoughts are developed in the
future, could they be employed not only by defendants hoping to demonstrate
innocence but also by prosecutors attempting to establish guilt? Could
prosecutors armed with a search warrant compel an unwilling suspect to submit to
brain scans aimed at exploring his or her innermost thoughts?
The
answer surely ought to be no. But getting to that answer isn’t as
straightforward as it might seem. The central constitutional question relates
to the Fifth Amendment, which states that “no person … shall be compelled in
any criminal case to be a witness against himself." In interpreting the
Fifth Amendment, courts have distinguished between testimonial evidence, which
is protected from compelled self-incriminating disclosure, and physical evidence,
which is not. A suspected bank robber cannot refuse to
participate in a lineup or provide fingerprints. But he or she can decline to
answer a detective who asks, “Did you rob the bank last week?"
So is the information in a brain scan physical or
testimonial? In some respects, it’s a mix of both. As Dov Fox wrote in a 2009
law review article, “Brain imaging is difficult to classify because it promises
distinctly testimonial-like information about the content of a person’s mind
that is packaged in demonstrably physical-like form, either as blood flows in
the case of fMRI, or as brainwaves in the case of EEG." Fox goes on to
conclude that the compelled use of brain imaging techniques would “deprive
individuals of control over their thoughts" and be a violation of the
Fifth Amendment.
But there is an alternative view as well, under which the
Fifth Amendment protects only testimonial communication, leaving the
unexpressed thoughts in a suspect’s head potentially open to government
discovery, technology permitting. In a recent law review article titled "A
Modest Defense of Mind Reading," Kiel Brennan-Marquez writes that “at
least some mind-reading devices almost certainly would not" elicit
“communicative acts" by the suspect, “making their use permissible under
the Fifth Amendment." Brennan-Marquez acknowledges that compelled
mind-reading would raise privacy concerns but argues that those should be
addressed by the Fourth Amendment, which prohibits unreasonable searches and
seizures.
That doesn’t seem right. It would make little sense provide
constitutional protection to a suspected bank robber’s refusal to answer a
detective’s question if the thoughts preceding the refusal — e.g., “since I’m guilty, I’d better not answer
this question" — are left unprotected. Stated another way, the right
to remain silent would be meaningless if not accompanied by protection for the
thinking required to exercise it.
And if that weren’t enough, concluding that compelled brain
scans don’t violate the Fifth Amendment would raise another problem as well: In
a future that might include mature mind-reading technology, it would leave the
Fourth Amendment as the last barrier protecting our thoughts from unwanted
discovery. That, in turn, would raise
the possibility that the government could get a search warrant for our
thoughts. It’s a chilling prospect — one that we should hope never comes to
pass.
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