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Don’t lie to my eyes (II.)

In my last post, I was talking about pupil of the eye. When you are measuring the pupil, you are probably using an eye tracker. And the eye-tracker provides us with more data than just pupil diameter. So today, we are going to look at the other data and what can be done with it.

Fixation and saccades

The measures the most eye-trackers can give as are gaze location, blinking frequency, time of the fixation and pupil dilation. This information can help us understand what information people acquire and where their focus is. This can be done using the measurement of fixations and saccaddes, [1]
Saccade is the time when your eyes are moving and it lasts about 15 – 40 ms. During this time, you are acquiring no information. Fixation is the time when your eyes stop and focus on a point. This is when your brain is processing the visual data. In silent reading fixation duration is on average 225 ms but may differentiate from 100 ms to 500 ms depending on the text. [2]

Cues to deception

When detecting deceptions, from the physiological signals that were tested in most studies, these eighteen were most successful; response length, details, response latency, rate of speaking, illustrators, eye contact, non-ah speech disturbances, silent pauses, filled pauses, posture shifts, hand movements, foot or leg movements, smiling (undifferentiated), nervous, pitch, blinking, self-fidgeting, and fidgeting (undifferentiated). [3]
Blinking can be evidence for deception in a way, that increased blinking can indicate anxiety or arousal, decreased blinking can on the other hand indicate greater cognitive effort. In non-interactive context liars blink significantly more than truth-tellers, in interactive context there was little difference. [3,4]
Gaze of the eyes can too be a clue for deception. Liars maintain less eye-contact with their interaction partner. If people are motivated to succeed in lying, they are more likely to decrease eye-contact. However if there is no special motivation, this effect is not present. [3,4]

Deception detection

When we are looking on the order of the fixations using saccades between the fixations, we can reconstruct how people conducted their task. This can tell us if people are trying to deceive us. In an experiment regarding personality evaluation, if people were trying to look good, they were more likely to first look at the more outermost answers within multi-choice scale question. On the opposite, when answering truthfully, the first gaze was focused more often on the center answers. [2]
Response time can be also obtained using eye-tracker. Eye-tracker can tell you when the subject have read the question and how long took him to answer it, you just have to log the time of the answer. This can too be helpful when detecting deception, because lying people are more likely to answer quicker or slower compared to telling truth, based on the task formulation. [2]
If lying is cognitively more complex than telling the truth, the number of fixations is expected to be higher while lying, because increase in fixation indicates increased cognitive load. [2]

Problems

There is no complex research or theory regarding detecting faking results in test, so we have to use methods and metrics created in research focused on general deception and lying. [2]
Gaze behavior and blinking are not so easily classified as pupil dilation and depend mainly on social scenario and experiment context. [4]
For gaze-contingent experiments, it is suggested that the experiment should be displayed on large high-refreshing (85-100Hz) CRT monitors instead of LCD panels. Due to physical limitations of liquid crystals, most LCD panels have a refresh rate of 60-75Hz. This would cause visual delay in gaze-contingent experiments. [1]

Conclusion

Response times, blinking and gaze detection can be useful clues for deception detection. From this measures, blinking was shown to be most successful in non-interactive measurements [4] so can be most useful for our project regarding online questionnaires.
Gaze detection in this context is not so useful, but based on the experiment can provide useful clues as the order of the fixations [2].
Response time can too be useful clue, but we have to be able to determine if the task is more or less cognitively demanding than telling the truth. [2]

References

[1] J. Wang, “Pupil dilation and eye tracking,” in A handbook of process tracing methods for decision research: A critical review and user’s guide, 2011, pp. 185–204.
[2] E. a. J. van Hooft and M. P. Born, “Intentional response distortion on personality tests: Using eye-tracking to understand response processes when faking.,” J. Appl. Psychol., vol. 97, no. 2, pp. 301–316, 2012.
[3] B. M. DePaulo, J. J. Lindsay, B. E. Malone, L. Muhlenbruck, K. Charlton, and H. Cooper, “Cues to deception.,” Psychol. Bull., vol. 129, no. 1, pp. 74–118, 2003.
[4] W. Steptoe, a Steed, a Rovira, and J. Rae, “Lie Tracking: Social Presence, Truth and Deception in Avatar-Mediated Telecommunication,” pp. 1039–1048, 2010.

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