## 1 Introduction
A study was conducted by the authors of [16] in Greece to validate the performance of the MMSE, and the result proved that an MMSE score of 23/24 is a credible test for diagnosis of dementia. Several well-designed serious video games have been proposed and should be helpful for evaluating cognitive abilities [10; 11; 17; 18; 19]. [PERSON], [PERSON] et al. [19] developed a serious game called _TrainBrain_, designed to improve concentration and to minimize the effects of the cognitive decline in attention for the elderly and children with ADHD (Attention Deficit Hyperactivity Disorder). In recent years, the products currently on the mainstream market for video and mobile games were designed for young people to experience exciting sight and sound stimulation, which may not be adaptable for the elderly. The development of a serious game is very challenging, especially when addressing dementia patients. Many factors must be considered, such as the needs of the subjects, human-computer interactions, emotions, comfortability, etc., which make development more complicated. A well-designed GUI (Graphical User Interface) is one of the most important aspects to help subjects focus on the game [20]. In [21], the authors built a whack-a-mole game for tablets (Android-based). The game was divided into different speeds, and the time was used to record the subject's score and response time. The authors proved that this game can be used to assess some executive functions, especially those related to inhibition, in their recent study [22]. They also suggested that this game can be developed for the elderly to assess other executive functions [22; 23]. In this present study, two serious games were designed to meet the standards of play for the elderly. The purpose of our PC-based games was to measure response performance (reaction time and accuracy rate). Psychologists and clinicians were continuously consultedduring system development to obtain a better understanding about the complexity of the external appearance of cognitive functions and the reactions of the elderly. Based on [22], first, we built a similar whack-a-mole game without distractors (the objects in addition to the mole) to focus only on reaction time and accuracy rate when playing the game, as the game's target is to collect information on the reaction time and accuracy rate of the subjects. Then, we designed the second game, hit-the-ball (with a distractor), also to assess judgment ability and to observe how the subjects distinguish between objects. Another issue, as explained in [24], is that elderly people may think that computers are not friendly for them, making these games uncomfortable to play. Therefore, our games were designed to be as simple as possible and easy to play, considering that the subjects are old and that most of them have never experienced playing PC-based games before. It was found that the traditional whack-a-mole machine game was a famous game in the past for Taiwanese people. We designed a special board-button to allow the subjects to be more familiar and comfortable with the game. In our discussion, we analyze and explain the response time and the accuracy rate as the dependent variables. We used the MMSE score (normal group, MCI group, and moderate-to-severe dementia group) and game level (slow, medium, and fast) as the independent variables. We also analyzed judgment ability for the hit-the-ball game. All results were calculated using statistical methods (Kruskal-Wallis Test and Friedman Test) for accuracy rate and one-way ANOVA for reaction time. We found that there are significant differences between these three categories of subjects.