Detecting deception: Effect of auditory and visual stimuli on pupil dilation

We investigated the effects of auditory and visual stimuli on pupil dilation induced by emotional arousal during deception. The 33 participants were free to select to be in either a guilty or a not-guilty group. The guilty group performed a theft crime mission, and the not-guilty group performed a legal mission. To detect deception, we measured their pupil diameter with an eye tracker, and they completed the Control Question Test that is typically employed in polygraph tests, and which is based on a comparison of physiological responses to crime-relevant questions and comparison questions. This test was presented via one of three stimuli: auditory, visual, or dual sensory (auditory and visual simultaneously). The findings revealed that the diameter of the pupils of the guilty group increased differently according to the question type when both auditory and visual stimuli were presented simultaneously. Results suggest that pupil dilation could be the deception discriminant, and the use of more than one sensory stimulus may support lie detection in forensic investigations.