Unmasking Deception: Detecting Lies in Spoken Discourse used in Courtroom Evidence

Author: Christa Cooper︱Editor: Vicky Strong

People don’t outright lie. It's a universal truth—but when deception presents itself in courtroom testimony, it can mean the difference between justice served and justice denied.

In the summer of 2023, I found myself seated among eleven other jurors in the jury box of my local Crown Court, grappling with a daunting question: How are twelve strangers expected to agree on who is telling the truth—the defendant or the prosecutor? Both parties were unwavering in their accounts, each asserting their version of events as the absolute truth. This dilemma led me to ponder: Are there specific linguistic cues in spoken discourse that reveal when someone is being dishonest?

Like facial expressions, changes in the tone or pitch of a person's voice are closely linked to the parts of the brain involved with emotion, such as the amygdala and limbic system. These brain regions play a key role in regulating emotional arousal, which can influence vocal prosody— causing shifts in pitch, tone, or speech rhythm.^[1] Emotions like anger, distress, or anxiety often present as noticeable changes in vocal characteristics.^[2] Research suggests that vocal changes can signal cognitive load or stress, both of which are often associated with lying.^[3] However, these prosodic features are not exclusively tied to lying; they can also be triggered by genuine emotional stress or anxiety, making it difficult to definitively determine the truthfulness of a statement based solely on such cues.^[4]

While changes in tone and pitch offer valuable insights, they are best used alongside other behavioural or verbal indicators to form a more comprehensive assessment of credibility, as multiple studies show the limitations of relying solely on vocal features for lie detection.^[5]

However, it is essential not to hastily label someone as dishonest based solely on a high-pitched response. Establishing an individual's baseline and natural tone of voice is crucial before drawing conclusions about the credibility of their statements.

This led me to question: How can I determine someone's baseline when my only reference is a few hours of high-pressure cross-examination in a courtroom?

Unfortunately, absolute certainty is unattainable. The fast-paced nature of courtroom testimony demands that jurors focus solely on the facts, disregarding emotion as a basis for evidence entirely. Therefore, we need to rely on other linguistic cues to assess if someone is being deceitful. This can include the prosecutor/defendant using overly formal language.^[6] While they are attempting to sound intelligent, this tactic presents itself in the courtroom as rehearsed and overly formal – which does not always reflect natural and spontaneous speech patterns. Burgoon and Buttler (1996) call this the Interpersonal Deception Theory (IDT).

Rather than blatantly lying, people often manipulate or distort the truth. They most likely create a fabricated story, embellishing details and carefully crafting their words to create the reaction they want out of the interaction- an attempt to sound more credible or convincing. Leading to cognitive overload, liars may also use fillers such as “umm” or ‘err” to mentally process their next fabrication and keep up with previous lies- filling in the awkward silence out of fear of scrutiny. Fillers also serve to deflect attention, remain in control of the conversation, and provide extra time to prepare a response.^[7]

Conversely, fillers are common in everyday speech patterns. Given the highly stressful environment of a courtroom, it is only natural to assume these “umms’ and “errs” are self regulatory speech cues - a reflection of anxiety or nervousness in the moment of interrogation. Someone who is being deceptive often distances or “dissociates” themselves from their statements as they lack personal experience.^[8] This can lead to slip-ups in the consistency of pronouns when recounting past events.

If we compare the statements “mistakes were made” to “ I made some mistakes” - we can see a lack of ownership and an attempt to disassociate responsibility solely from omitting the personal pronoun “I”.^[9] Defensiveness is also linked to the lack of personal pronouns in Court testimonials.^[10] In tandem, this may be a psychological coping mechanism to distance themselves from accepting any personal responsibility.

While the desire to be a human lie detector will always be top on my wish list– humans are deceptive animals at heart. Deception in a courtroom has so many influencing external factors both person and context-dependent, that obtaining this knowledge of lie detection is proving tougher and tougher to distinguish. Even artificial intelligence, designed to be objective, has begun crafting its own fabrications in the name of self-preservation. Perhaps, the greatest deception of all is believing we can ever truly separate fact from fiction.^[11]

References

[1] Grandjean, D., Sander, D., Pourtois, G., Schwartz, S., Seghier, M.L., Scherer, K.R. and Vuilleumier, P., 2005. The voices of wrath: brain responses to angry prosody in meaningless speech. Nature neuroscience, 8(2), pp.145-146.

[2] Banse, R. and Scherer, K.R., 1996. Acoustic profiles in vocal emotion expression. Journal of personality and social psychology, 70(3), p.614.

[3] Zuckerman, M., Koestner, R. and Driver, R., 1981. Beliefs about cues associated with deception. Journal of Nonverbal Behavior, 6, pp.105-114.

[4] Vrij, A., 2019. Deception and truth detection when analyzing nonverbal and verbal cues. Applied Cognitive Psychology, 33(2), pp.160-167.

[5] Ekman, P. and O'Sullivan, M., 1991. Who can catch a liar?. American psychologist, 46(9), p.913.

[6] Buller, D.B. and Burgoon, J.K., 1996. Interpersonal deception theory. Communication theory, 6(3), pp.203-242.

[7]Goffman, E., 2023. The presentation of self in everyday life. In Social theory re-wired (pp. 450-459). Routledge.

[8] Mehrabian, A., 1971. Nonverbal betrayal of feeling. Journal of Experimental Research in Personality.

[9] L. Knapp, M. and Comaden, M.E., 1979. Telling it like it isn't: A review of theory and research on deceptive communications. Human Communication Research, 5(3), pp.270-285.

[10] Feldman Barrett, L., 2011. Constructing emotion. Psihologijske teme, 20(3), pp.359-380.

[11] Starr, B., 2024.,AI has already become a master of lies and deception, Scientists warn., Science alert, Tech, https://www.sciencealert.com/ai-has-already-become-a-master-of-lies-and-deception-scientists-warn . Accessed 22/01/2025