## 4 Discussion
Very limited social interaction elements were also reported in the reviews of [53; 55], and it seems that this field has not received any more attention, which can be justified as a complex element that requires extensive implementation. Moreover, interacting with others and being exposed may cause negative effects for participants, such as anxiety and frustration, especially in high-risk cases. Finally, avatars were used less compared to the narrative context (N = 22), which was used with the purpose of providing a context to the trained activity and adding meaningful content for the user. Regarding sample characteristics, studies varied in terms of sample size between 5 [70] and 794 [78]. Nearly one third of studies (29.5%) had 20 to 59 participants, and 38.6% included 60-99 participants. However, only 7 studies had 100 and above participants. It is a fact that gamification has a broad variety of target audiences, as it has been applied to children, adolescents, adults and the elderly. The systematic review revealed a balance between target groups, since 36.36% of the studies targeted children and adolescents, 29.54% included adult participants less than 60 years old and 34.1% had participants over 60 years old. Thus, there is a slight preference to children and older people in studies of gamification. Between samples, most of the studies targeted healthy (low-risk) participants, and 43% of studies targeted several forms of cognitive impairments, such as ADHD, autism spectrum disorder, multiple sclerosis, etc. It seems that gamified WM training was used not only as a therapeutic/rehabilitation tool, but it was also used to support and foster healthy people in order to cognitively function at higher rates or as a preventative tool for cognitive decline. However, gamification cannot be applied in the same way to every target group, since users can vary in training goals, motivation and cognitive level. It is necessary to provide personalized and adaptive training programs according to individual users. For example, the presented context may be suitable for kids, but it might look childish or unrealistic to adults and older people. Nevertheless, the systematic review spotted common patterns in gamification development for the three target groups, as it seems that Conflict, Difficulty Adjustment, Action Points, Feedback and Progression were the four common elements that were frequently used in all three categories. Gamified WM training has been offered in a variety of devices according to the findings of this review; however, the most dominant device was a computer (PCs or laptops), as reported in 52% of the studies, with tablets/smartphones coming in second (38.6%). On the other hand, gaming consoles and virtual reality equipment were used less. Especially for studies including VR, they were primarily studies which gamification was utilized in evaluation and assessment of cognitive tasks. An interesting finding is associated with older people, as 10 studies used tablet devices, and only 4 cases made use of computers, verifying the fact that tablets and smartphones with touch functionality are more suitable for older adults, which differentiates from the findings in [53], which reported that none of the studies that used older adults as participants reported tablets as game platforms. Therefore, it looks as though progress has been made in this direction. Intervention sites were split across participants' homes and laboratories (36% and 34%, respectively), and there was a study that included both sites, having some sessions under laboratory conditions and some at home [90]. It seemed to be the case that gamified WM training can be equally feasible and effective either in laboratory or house conditions, providing the freedom of training everywhere and at any time and ensuring that transportation is not a limit that may hinder adherence. Finally, 63.5% of studies reported over 15 sessions, and some of them had single-session designs (11.5%).