## 1 Introduction  
The World Health Organization (WHO) estimates that around 50 million people have dementia, with nearly 10 million new cases every year [1]. Dementia refers to deterioration of cognitive function in the elderly. This syndrome affects memory, thinking, orientation, comprehension, calculations, learning capacity, language, and judgment. It also affects individual quality of life and is a financial burden for families due to expensive costs for healthcare [2]. According to the Alzheimer's association (2019), 36% of people aged 85 or older have Alzheimer's Disease (AD) [3]. Dementia and other cognitive impairment diseases have become an important global issue, as the number of elderly people is increasing. In 2025, it is predicted that Taiwan will become a super-aged society (National Development Council in Taiwan, 2016). As age increases, problems in cognitive abilities, such as divided attention, memory decline, etc., also increase [4]. Simple reaction times are valid for measuring cognitive function in both patients and normal subjects [5]. Furthermore, the authors in [6] also noted that accuracy rate can correlate significantly with episodic memory performance and other cognitive functions. Reaction time and accuracy rate are thus related to cognitive functions [5; 7; 6]. Most previous research used neuropsychological tests, such as the Flanker test, the CambridgeNeuropsychological Test Automated Battery, and Repeatable Battery for the Assessment of Neuropsychological Status [6; 7]. Therefore, in this study, our main objective is to determine the difference in the reaction time and accuracy rate between the aforementioned three categories of subjects (normal subjects, Mild Cognitive Impairment (MCI), and dementia) using our own designed serious games. We intended to determine whether the response performance (also mentioned in [7]) can differentiate between these three categories. A study by [PERSON] et al. [8] found that patients with MCI and Alzheimer's disease had significantly longer reaction times than normal aging control groups, with reaction times that did not eliminate individual differences. When the factors related to the different reaction times of individuals are excluded, patients with MCI actually behaved similarly to the normal aging control group, but the responses of patients with Alzheimer's disease, after excluding the effects of individual differences, were still not as good as those of the other two groups. Numerous methods have been developed to examine Alzheimer's disease and MCI. Invasive methods are used to collect data from inside the human body and are not considered safe and comfortable for subjects [9]. [PERSON] et al. [10] found that using noninvasive methods like serious games can detect the onset of MCI or Alzheimer's disease. In our study, we applied the same method noninvasively by designing PC-based serious games to evaluate the reaction times and accuracy rates related to the cognitive abilities among normal subjects, MCI subjects, and dementia subjects. Our approach was to compare the results of the performance of an elder individual when playing the game using neuropsychological tests of cognitive function based on the MMSE (Mini Mental State Examination). There are many neuropsychological tests and clinical questionnaires used to assess dementia levels among the elderly. Clinical questionnaires, such as the Mini Mental State Examination (MMSE) [11] and the Montreal Cognitive Assessment (MoCA) [12], are a popular way to evaluate cognitive abilities via clinical measurements. [PERSON] et al. [13] used an Augmented Reality (AR) serious game called Smartkuber to perform cognitive screening among the elderly. To validate the relationship between game results and MoCa results, the authors used the Pearson correlation statistical method [13; 14; 15]. In our research, we use the MMSE to evaluate the level of dementia among the elderly due to the heterogeneity of the age-group.