Load-Dependent Relationship Between Lateral Prefrontal Cortex Activity and Pupil Diameter in the Context of Driving

Assessing arousal and cognitive load in the context of driving is important because inappropriate arousal and cognitive load increase the risk of accidents. Previous studies using n-back tasks showed that both lateral prefrontal activity and pupil diameter are good indicators of cognitive load. However, the relationship between lateral prefrontal activity and pupil diameter was load-dependent, and a significant positive correlation was observed in the low-load 0-back condition but not in the high-load 3-back condition. In this study, we utilized Near-Infrared Spectroscopy (NIRS) and eye tracking to investigate the load-dependent relationship between lateral prefrontal cortex activity and pupil diameter in the context of driving. Participants drove on a mountain pass using a commercially available driving game, with and without engagement in a secondary conversation task. The NIRS and eye tracker experiments were conducted separately. The results showed that the pupil diameter and Oxy-Hb concentrations in the dorsolateral prefrontal cortex increased significantly in the driving condition that included the conversation task compared to the normal driving condition. Furthermore, we found a significant positive correlation under the high-load conversational driving condition, in which individuals with larger pupil diameters showed greater left dorsolateral prefrontal cortex activity, but not so under low-load normal driving condition. Our findings provide further evidence of a load-dependent relationship between lateral prefrontal cortex activity and pupil diameter and reveal that the relationship was not simply dependent on the degree of cognitive load but also on the nature of the task, possibly due to the differential engagement of executive function and arousal.