Multiple Factors Mental Load Evaluation on Smartphone User Interface

Abstract

Smartphone is nowadays the most prevalent computer system, thus a lot of attention from academia and industries has been put to evaluate its quality of use. However, Smartphone has more complex interaction modes and usage scenarios than PC and laptop. And therefore assessing its quality using a conventional usability evaluation is not sufficient. Meanwhile, the mental load serves as an acknowledged index of effort that operators have put in human-machine interaction, especially under high-demanding context. Mental load contains a set of parameters in multiple dimensions, such as primitive task performance, biological measurement(s) and subjective mental load scale, which assesses the efforts of tasks under a particular environment and operating conditions. Thus, it is suitable for evaluating complex mental work, and may indicate the use of Smartphones.

The aim of this paper is to apply a multi-dimensional method to assess the mental load of users, and find out which measurement(s) is the most suitable one to evaluate the efforts for using a smartphone. During this study, the effort on conducting tasks with four difficulty levels were assessed using measurements in three dimensions, which were (1) user performance (task accomplishment and secondary task), (2) subjective rating (NASA-TLX scale) and (3) physiological function (EDA). The values of these measurements were compared across novice, average and skilled users. The results show that: task duration and number of usability error are significantly related with mental load and change with the difficulty level of tasks; in subjective rating, Mental Demand, Effort and Frustration were highly related with mental load.