OBJECTIVE: The objective of this study is to investigate the whether multi-tasking performance in (three-dimensional) 3D aid or impede cognition compare to (two-dimensional) 2D environments, as reflected by cognitive load. Specifically, we aim to examine the mechanism of multi-tasking under 3D (virtual reality [VR]) and 2D (PC monitor) conditions using the widely used Multi-Attribute Task Battery (MATB) II paradigm. METHODOLOGY: The MATB-II sub-tasks, namely "Tracking" and "System Monitoring," were conducted with varying task demands in both 3D conditions (Tracking Far - System Monitoring Near [TF-SN], Tracking Near - System Monitoring Far [TN-SF]) and a 2D condition with no depth perception (No Depth [ND]). Participants' cognitive load was assessed using subjective reporting (NASA-TLX) and physiological measure (root mean square of successive difference (RMSSD) of heart rate variability (HRV)). RESULTS: The study found that performance was significantly better in the ND condition compared to the TF-SN and TN-SF conditions. Furthermore, higher NASA-TLX scores and lower RMSSD values were observed in the TF-SN and TN-SN conditions compared to the ND condition, providing additional support for the overall findings of the MATB-II paradigm. CONCLUSION: These findings suggest that processing multiple tasks in different depth planes may lead to poorer performance and increased subjective and physiological cognitive load.