Interface design has a large impact on the usability of a system, and the addition of multitasking only makes these systems more difficult to use. Information processing, mental workload, and interface design are determining factors that impact the performance of usability, and therefore interface design needs to be more adapted to users undergoing a high mental workload. This study examines how a primary task, visual tracking, is affected by a secondary task, memory. Findings show that a high mental workload effects reaction time and memory performance on layouts with a high index of difficulty. Further research should analyze the effects of manipulating target size and distance apart independently from manipulating the index of difficulty on performance.