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Evaluating physical discomfort of designed gestures is important for creating safe and usable gesture-based interaction systems; yet, gestural discomfort evaluation has not been extensively studied in HCI, and few evaluation methods seem currently available whose utility has been experimentally confirmed. To address this, this study empirically demonstrated the utility of the subjective rating method after a small number of gesture repetitions (a maximum of four repetitions) in evaluating designed gestures in terms of physical discomfort resulting from prolonged, repetitive gesture use. The subjective rating method has been widely used in previous gesture studies but without empirical evidence on its utility. This study also proposed a gesture discomfort evaluation method based on an existing ergonomics posture evaluation tool (Rapid Upper Limb Assessment) and demonstrated its utility in evaluating designed gestures in terms of physical discomfort resulting from prolonged, repetitive gesture use. Rapid Upper Limb Assessment is an ergonomics postural analysis tool that quantifies the work-related musculoskeletal disorders risks for manual tasks, and has been hypothesized to be capable of correctly determining discomfort resulting from prolonged, repetitive gesture use. The two methods were evaluated through comparisons against a baseline method involving discomfort rating after actual prolonged, repetitive gesture use. Correlation analyses indicated that both methods were in good agreement with the baseline. The methods proposed in this study seem useful for predicting discomfort resulting from prolonged, repetitive gesture use, and are expected to help interaction designers create safe and usable gesture-based interaction systems.

Automotive gear shifters are among the most important control devices in driving tasks, and their user-centered design has a direct impact on the driving performance and safety. In recent years, shift-by-wire systems with electronic shift buttons have replaced conventional transmission systems due to their advantages, such as the ease of shifting and space utilization inside vehicles. However, there are no minimum requirements or specific regulations for electronic shift button layouts. Thus, different car manufacturers and models have adopted different layouts, and this in turn has induced the risk of driver confusion/error in the shifting operation. Therefore, this study aimed to evaluate the ergonomic performance of different electronic shift button layouts and examine the variance in performance depending on driving experience. Here, 21 survey respondents with different levels of driving experience subjectively evaluated 12 different shift button layouts for 7 ergonomic evaluation measures (accuracy, convenience, rapidity, learnability, intuitiveness, safety, and preference). The outcomes of the study elucidate ergonomic layouts that receive high rankings in each driving experience group (all, novice, and experienced drivers) and principles that should be considered when designing shift button layouts for each group. These findings are expected to contribute to the ergonomic design and international standardization of shift button layouts, thereby preventing driver confusion/errors and improving road safety.

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