The Effect of Cognitive Load and Emotional Arousal on Liar’s Pupil Diameter Changes

Abstract

Purpose : Liars experience emotional arousal because of anxiety or a sense of guilt, but also are influenced by cognitive load since lying is more cognitively demanding than truth telling. The purpose of this study is to examine the effects of emotional arousal and cognitive load on pupil diameter during lie detection interview. We hypothesize that the guilty group for the detection of the lie will have a larger pupil size change than the innocent group for the cognitive load question.

Methods : The guilty group (n = 30) committed a mock crime (i.e., stealing cash) and the innocent group (n = 30) performed a mission (i.e., sending a message) in the research assistant’s office. After that, their pupil size was measured using a wearable eye-tracker during the interview. The interview questions were classified with the 3 emotional arousal, 3 cognitive load, and 3 neutral questions. The pupil dilation was defined as a difference between the first sample and each subsequent sample for a period of 6000 ms provided changes in pupil size over time from answering onset. If the pupil size was further increased in the cognitive load question than in the emotional arousal question, the difference appears to be a positive value, which means that the participant was more affected by the cognitive load in lying.

Results : As a result of analysis, interaction between group and time was significant, F (1, 56) = 2.838, p <.05, η² = .048, which means that pupil size variation was significantly different between the two question types. The main effect of group was not significant, F (1, 56) = 2.556, p = n.s., η² = .044, and the main effect of time was not significant, F (1, 56) = 1.793, p = n.s., η² = .031. In order to confirm the interaction between group and time, we conducted independent sample t-test for each time interval. The difference in pupil size variation between the two question types was significant in the 1000 ms and 2000 ms intervals. This means that the pupil size of the guilty group increased more in the cognitive load question than the emotional arousal question for 2000 ms compared to the innocent group.

Conclusions : We confirmed that the cognitive approach is more effective in explaining the lie, and we confirmed that it is possible to increase the lie detection rate by asking questions that increase the cognitive load rather than emotional arousal at the interview.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.