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Can the Eyes Betray a Liar? Insights from Eye Tracking and Pupillometry

by | Jun 1, 2025 | Manuscripts | 0 comments

Palak Kodan1, B.Optom. Student;

Roshni Sengupta 2, Assistant Professor

GD Goenka University, Gurugram, India

 

Deception is a common part of daily human communication, influencing interactions across personal, professional, and legal contexts. Early research has indicated that individuals typically tell one to two lies daily. Due to its prevalence, there has been long-standing interest in detecting lies through reliable verbal and nonverbal cues, using both observational methods and advanced technologies like polygraphs, voice-stress analysis, electroencephalography (EEG), eye-tracking, and functional magnetic resonance imaging (fMRI). (1)

Pupil Dilation as a Measure of Deception

Pupil dilation is an involuntary response influenced by factors such as ambient light, stress, cognitive effort, arousal, and emotional states, driven by autonomic nervous system activity. As it occurs unconsciously, pupillary changes may provide reliable insight into a person’s internal state and are considered a potential indicator of deception. (2)

Research supports the use of pupil dilation as a cue to lying. Deception often involves cognitive load and emotional arousal, both of which cause increased pupil size. (3) Early findings showed that deceptive responses triggered greater dilation when critical questions were introduced, (4) while another study also found larger pupil sizes during lies compared to truthful answers. (5) Studies consistently show that pupil dilation increases during deceptive behaviour. (6) Research indicates that individuals exhibit larger pupil sizes when lying compared to telling the truth, with dilation often occurring both before and after the act of deception. (3) Greater pupil responses have also been observed during cheating for rewards and in guilty individuals reacting to crime-related cues, highlighting the link between deception and autonomic arousal. (7,8) Another investigation noted that lying individuals experienced pupil dilations ranging between 4% and 8% of their original diameter. (9)

Blink Rate and Deception Detection

Blinking behaviour is a valuable indicator in lie detection. During deception, individuals typically exhibit a noticeable decrease in blink rate, followed by a rapid increase shortly after the lie is told. EEG-based analyses utilising blink rate have demonstrated high accuracy in detecting deception, with some studies reporting up to 95.12% accuracy. (10) One study observed that the number of blinks increased up to eight times compared to the baseline blink count before a question was posed. (9) In a psychological experiment, researchers examined blink count and duration related to personal and lifestyle topics such as name, age, residence, and marital status. Results revealed that both blink duration and blink count were significantly higher during deceptive responses. (11) Additionally, it was reported that blink latency, the time between stimulus onset and blink initiation, was delayed due to the cognitive and motor demands associated with lying. (12)

Eye Movements for the False Answers

The eyes are highly expressive and often considered indicators of honesty. Neuro-Linguistic Programming (NLP) suggests gaze direction reflects truthfulness, left for recalling truth and right for fabricating lies though studies found no evidence supporting this.(13) One study proposed that liars show fewer eye movements due to increased cognitive load associated with internal processing, prompting a decrease in attention to external stimuli and the effort to maintain eye contact.(14,15) Rehearsed liars displayed the least movement to reduce distraction and recall their lies. Another study found liars used more deliberate eye contact than truth-tellers and admitted doing so to convince interviewers and gauge believability. (16)

Conclusion

Eye-related cues such as pupil dilation, blink patterns, and eye movements offer valuable insights into deceptive behaviour, reflecting the cognitive and emotional load involved in lying. While not foolproof, these physiological and behavioural indicators enhance the understanding and potential accuracy of lie detection methods.

 

References:

  1. Trifiletti E, D’Ascenzo S, Lugli L, Cocco VM, Di Bernardo GA, Iani C, Rubichi S, Nicoletti R, Vezzali L. Truth and lies in your eyes: Pupil dilation of White participants in truthful and deceptive responses to White and Black partners. Plos one. 2020 Oct 13;15(10):e0239512.
  2. Kret ME, Fischer AH, De Dreu CK. Pupil mimicry correlates with trust in in-group partners with dilating pupils. Psychological science. 2015 Sep;26(9):1401-10.
  3. Wang JT, Spezio M, Camerer CF. Pinocchio’s pupil: using eyetracking and pupil dilation to understand truth telling and deception in sender-receiver games. American economic review. 2010 Jun 1;100(3):984-1007.
  4. Berrien FK, Huntington GH. An exploratory study of pupillary responses during deception. Journal of Experimental Psychology. 1943 May;32(5):443.
  5. Heilveil I. Deception and pupil size. Journal of Clinical Psychology. 1976 Jul 1;32(3).
  6. Dionisio DP, Granholm E, Hillix WA, Perrine WF. Differentiation of deception using pupillary responses as an index of cognitive processing. Psychophysiology. 2001 Mar;38(2):205-11.
  7. Hochman G, Glöckner A, Fiedler S, Ayal S. “I can see it in your eyes”: Biased processing and increased arousal in dishonest responses. Journal of Behavioral Decision Making. 2016 Apr 7;29(2-3):322-35.
  8. Lubow RE, Fein O. Pupillary size in response to a visual guilty knowledge test: New technique for the detection of deception. Journal of Experimental Psychology: Applied. 1996 Jun;2(2):164.
  9. Nugroho RH, Nasrun M, Setianingsih C. Lie detector with pupil dilation and eye blinks using hough transform and frame difference method with fuzzy logic. In2017 International conference on control, electronics, renewable energy and communications (ICCREC) 2017 Sep 26 (pp. 40-45). IEEE.
  10. Immanuel J, Joshua A, George ST. A study on using blink parameters from EEG data for lie detection. In2018 International Conference on Computer Communication and Informatics (ICCCI) 2018 Jan 4 (pp. 1-5). IEEE.
  11. George S, Pai MM, Pai RM, Praharaj SK. Eye blink count and eye blink duration analysis for deception detection. In2017 International conference on advances in computing, communications and informatics (ICACCI) 2017 Sep 13 (pp. 223-229). IEEE.
  12. Fukuda K. Eye blinks: new indices for the detection of deception. International Journal of Psychophysiology. 2001 Apr 1;40(3):239-45.
  13. Wiseman R, Watt C, ten Brinke L, Porter S, Couper SL, Rankin C. The eyes don’t have it: Lie detection and neuro-linguistic programming. PloS one. 2012 Jul 11;7(7):e40259.
  14. Walczyk JJ, Griffith DA, Yates R, Visconte SR, Simoneaux B, Harris LL. Lie detection by inducing cognitive load: Eye movements and other cues to the false answers of “witnesses” to crimes. Criminal Justice and Behavior. 2012 Jul;39(7):887-909.
  15. Vrij A, Mann S, Leal S, Fisher R. ‘Look into my eyes’: Can an instruction to maintain eye contact facilitate lie detection?. Psychology, Crime & Law. 2010 May 1;16(4):327-48.
  16. Mann S, Ewens S, Shaw D, Vrij A, Leal S, Hillman J. Lying eyes: Why liars seek deliberate eye contact. Psychiatry, Psychology and Law. 2013 Jun 1;20(3):452-61.

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