Dual-Task Performance as a Measure of Mental Effort in Searching a Library System and the Web

This paper examines a dual-task method for the assessment of mental effort during online searching, having the users engage in two tasks simultaneously. Searching was assigned as a primary task and a visual observation was set up as a secondary task. The study participants were asked to perform two searches, one on the Web and the other in a webbased library system. Perceived search difficulty and mental effort for searching on the two types of systems were compared through participant self-reports, dual-task performance, and search log analysis. After the searches were completed, the subjects reported that library searching was more difficult to conduct and they had to concentrate more than when Web searching. However, the results of dual-task performance do not reveal much difference in mental effort or concentration during searches in the two systems. Rather, they invested mental effort differently when viewing search results and reading retrieved documents. The findings indicate that a dual-task method provides a useful technique to measure mental effort in online searching, and it has a great potential to be used to measure other aspects of information retrieval such as task complexity and multitasking information behavior.