Contrary to popular beliefs, manual assembly at production is a mentally demanding task. With current trends of rapid prototyping and smaller production lot sizes, this will result in frequent changes of assembly instructions that have to be memorized by workers. Assistive systems can compensate this expected increase in mental workload, specifically working memory load, by providing “just-in-time” assembly instructions through in-situ projections. The implementation of such systems and their benefits to reducing mental workload have previously been justified with self-perceived ratings or think-aloud studies. However, there is no evidence by objective measures if mental workload is truly reduced by in-situ assistance. In our work, we showcase electroencephalography as a complementary evaluation tool to assess the cognitive demand placed by two different assistive systems in an assembly task, namely paper instructions and in-situ projections. We identified the individual electroencephalographic bandwidth that varied with changes in working memory load.We show, that changes in the corresponding bandwidth are found between paper instructions and in-situ projections, indicating that they reduce working memory compared to paper instructions. These findings converge with NASA-TLX questionnaire responses for subjective workload. Methodically, the current work contributes by demonstrating how design claims of cognitive workload alleviation can be validated. Moreover, it directly validates the use of engineered assistive systems for delivering context-aware information. Finally, we analyze the characteristics of electroencephalography as real-time assessment for cognitive workload to provide insights regarding the mental demand placed by assistive systems.
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