While the Machine Speaks for us: An Investigation into the Use of Neural Speech Decoding as Testimonial Evidence in Law

Tristan Borresen

University of Edinburgh

The advancement of inferring inner speech from brain signals (NSD) challenges the notion of testimony in law and epistemology. To testify is typically to put into words with one’s voice one’s convictions, memories, desires, —but what if by scanning one’s brain someone could do this independently of one’s vocalizations, and, not to say, will?
In this presentation, I warn against an idea defended by Nita Farahany that information from NSD could produce testimonial evidence. My contention is that NSD and testimonies differ in their epistemic status. While the evidential validity of testimony depends essentially on the person’s sincerity, we evaluate NSD upon the accuracy of decoding the person’s inner speech.
To show this, I first explore how NSD poses a problem to self-incrimination rights in, for instance, the Fifth Amendment to the US Constitution, protecting individuals from testifying against themselves. Building on Pardo’s epistemic account of the distinction between physical and testimonial evidence, I argue that since NSD produces ambiguous information, it does not qualify as testimony. Conversely, by denouncing my thesis, one is liable to commit what I call the informational symmetry fallacy (ISF): the fallacious conflation of the decoded output of the brain with the person’s speech act.

I then identify the consequence of committing ISF by attacking Farahany’s proprietary notion of thought. This notion stems from her aim of presenting a new taxonomy of evidence more suited for constitutional rights regarding brain data and privacy. Here, I argue that Farahany must presume that we already own and thereby are accountable for the intercepted thoughts. Hence, she precludes the possibility of disclaiming our thoughts, and thereby justifies others in taking them as our beliefs independently of our epistemic authority.
I finally discuss a problem ensuing from my account, namely that users of neural speech prostheses cannot qualify as witnesses in a legal setting. Here, I argue that although NSD prosthetics enable users to communicate, we could not assess user’s testimonial sincerity on behalf of the NSD readout. Because of this, I conclude that NSD is analogous to hearsay evidence.

Chair: Ryan McLaughlin

Time: September 13th, 14:00-14:30

Location: SR 1.006