Neuroscience, Mental Privacy, and the Law
Shen, Francis X., Harvard Journal of Law & Public Policy
III. MIND READING WITH NEUROIMAGING: WHAT WE CAN (AND CANNOT) DO
Having established in Part II a working definition of neuroimaging mind reading, the Article now briefly discusses several recent legal applications of such technology. Part III reviews: (A) fMRI-based lie detection; (B) fMRI-based memory detection; (C) EEG-based memory detection; and (D) fMRI-based decoding and reconstruction of visual stimuli.
A. Lie Detection with fMRI (127)
Neurons, the cells of greatest interest in the brain and nervous system, need oxygen to live. This oxygen is supplied to them via blood flow. fMRI is premised on the logic that tracking relative blood flow to different parts of the brain will reveal relative oxygen uptake, and thus show which neurons are more active (at a given moment in time). (128) Changes in blood oxygen levels in the brain at different moments during a given experimental task allow for inferences about brain-activation patterns.
Different protocols have been used in fMRI lie detection, most of which rely on a paradigm known as the "Concealed Information Test" (CIT) (also known as the "Guilty Knowledge Test" (GKT)). (129) This paradigm is different than the Control Question Test typically used by professional polygraphers. (130)
fMRI lie detection evidence has been proffered in several U.S. cases, has been the topic of much neuroscience research, and has drawn the attention of many commentators. (131) There are a large number of conceptual and technical problems with this approach. Conceptually, one major challenge with neuroimaging lie detection is defining a "lie." (132) In practice, neuroscience lie detection has utilized an "instructed lie" experimental paradigm, (133) in which subjects are told to lie under certain conditions in the experiment. Critics point out that this may limit the inferences we can make about "lying," because an instructed lie in the lab may not involve the same brain activity as a high-stakes lie in real life outside the lab. (134) Additionally, technical issues include general concerns about using fMRI techniques to study higher-order cognitive functions. (135)
Of particular note here is the "reverse inference" fallacy. The reverse inference fallacy is the idea that just because a particular part of the brain is more active during a certain cognitive state, it does not necessarily follow that whenever that brain area is more active, a person is in that cognitive state. (136) The reverse inference fallacy is acute in the lie detection case, as "it is not lying per se that is being decoded from these brain areas but rather the cognitive and emotional processes that are associated with lying." (137)
Despite these limitations, two for-profit fMRI-based lie detection companies are now in operation, (138) and both have proffered evidence in criminal trials on behalf of defendants. (139) So far, the evidence has been ruled inadmissible under both the Daubert standard in federal court (140) and the Frye standard in state court. (141) However, the judge overseeing the evidentiary hearing in the federal case suggested that such evidence may one day become admissible:
[I]n the future, should fMRI-based lie detection undergo further testing, development, and peer review, improve upon standards controlling the technique's operation, and gain acceptance by the scientific community for use in the real world, this methodology may be found to be admissible even if the error rate is not able to be quantified in a real world setting. (142)
For purposes of the Fourth Amendment and Fifth Amendment analysis in Part IV, it is important to note that all of these experimental paradigms involve researcher-subject interaction such as requesting a response to a visual stimulus or question. (143) Although fMRI may be used in what is known as "resting state" analyses (in which the subject just lies in the scanner), such resting-state approaches have not been employed in the lie detection context. …