## 1 Introduction  
Stroke is a leading cause of permanent disability, affecting nearly 800,000 individuals every year in the United States alone [1]. Although motor impairments are a hallmark of stroke, cognitive impairments are also prevalent in chronic-stage stroke survivors. These cognitive impairments are marked by, but not limited to, diminished memory, attention, and executive function [2, 3]. In addition to affecting patients' activities of daily living and quality of life, prior studies have shown that cognitive impairments can serve as a significant barrier to engagement in motor rehabilitation [4], thus affecting the recovery of motor function [5, 6]. Moreover, it has previously been reported that cognitive impairments are associated with a decrease in the long-term survival rate [2] and increased symptoms of depression [7], which could lead to a deterioration of patients' perceived well-being [8; 9]. Therefore, stroke survivors with cognitive impairments often experience difficulty achieving independent living [2], which results in an increased rate of institutionalization [10] and cost of care [11]. The high financial burden of stroke care often drives the clinical communities to actively consider discharging stroke survivors early and engaging them with rehabilitation therapies in their residential settings [12]. However, patients have thus far shown poor adherence to rehabilitation therapies when close supervision by therapists is absent--for instance, in their home settings--thereby jeopardizing their continued recovery and maintenance of their function [13]. Therefore, it is essential to devise effective and engaging therapeutic interventions that can be self-administered by stroke survivors where access to therapists or in-person therapy is limited (e.g., patients with mobility limitation or in rural/underserved areas). Computer-based cognitive training tools have received tremendous interests in the clinical and research communities to enable patients to self-administer therapy in their home and community settings [14; 15; 16]. However, patients who self-administer computer-based remote training often show poor adherence, and therapists' frequent involvement was necessary to maintain patients' engagement to the intervention [17]. As a potential means to enhance patients' adherence to at-home cognitive training, serious games have been considered to be a viable solution for a wide range of populations, including healthy older adults [14; 18], persons with mild cognitive impairments and/or neurological conditions [19; 20; 21], and survivors of acquired brain injury such as stroke and traumatic brain injury [15; 16]. Serious games are video games designed for a primary purpose other than entertainment and enjoyment, such as educating, informing, and enhancing patients' health-related conditions [22; 23; 24]. Serious games can complement conventional therapeutic programs to provide additional training in remote settings [25; 26]. The entertainment components of serious games are an advantage to improve patients' compliance to seemingly mundane, repetitive therapeutic activities (e.g., non-game-assisted, computer-based cognitive training) [27], which are a major barrier hindering patients' potential functional recovery [28]. Furthermore, serious games could improve patients' engagement during therapeutic activities, which may lead to greater neuroplastic changes and functional recovery in brain injury survivors [29]. Serious games for cognitive training in stroke survivors must be carefully designed to provide simple and user-friendly interfaces so that stroke survivors with motor and cognitive impairments can interact with the interfaces (e.g., a touchscreen or joystick) of the game systems without caregivers' close assistance outside the clinical setting [30]. However, existing game-assisted cognitive training solutions do not provide adequate interfaces for individuals with some degree of motor impairments.