# Interactions in Augmented and Mixed Reality: An Overview
## 1 Introduction  
Significant efforts have been spent, in both basic and applied research, to highlight the importance of human-computer interaction (HCI) on the end-user experience in augmented and mixed reality (AR)(MR) environments [1, 2]. To a large extent, research focuses on the user capability to perform tasks and interact with the virtual world, assisted by various functions and control systems. User-centered system design (UCSD), first described by [PERSON] [3] and later by [PERSON] [4], generally focuses on the user's understanding of a system. It examines what the user expects to happen, and how to perform a task or recover from an error, presenting HCI as a communicative and collaborative process between humans and machines. Exploiting immersive realities and the UCSD radically changed the way humans perform everyday tasks or perceive historical and cultural information. Mixed and augmented reality finally occupy significant space in our daily routine. The achievement of several historical milestones, from routing [5] to entertainment [6], and from social media [7] to engineering and remote collaboration [8], showcases the promising future of AR and MR. Technological achievements in AR and MR environments have made possible interactive visualizations of previously unexplored virtual and real-world combinations. According to [PERSON] et al. [9], the MR environment is where the real and the virtualcoexist. [PERSON] et al. [10] described a mixed object as a real object with a virtual equivalent. Recently, [PERSON] et al. [11] defined the MR ecosystem, strictly separating it from AR, by introducing geospatial modalities and implementing the concept of mixed objects, thus achieving spatial and context awareness among realities. Over the past 25 years, approximately since the introduction of the well-known reality-virtuality continuum [9], published research work and applications have profoundly changed the way humans perceive and interact with historical [12; 13; 14; 15; 16], future [17; 18; 19; 20; 21], and imaginary [22; 23; 24] reality scenarios. However, the latest research findings and innovations in review papers regarding interaction methods are not classified under a well-defined framework, thus leading to misconnections and ambiguities. For example, having the taste, smell, and haptic modality enclosed by the sensor-based modality, a system that utilizes all of them would still be, by definition, unimodal. [PERSON] [25] and [PERSON] [26] both stated that the interaction between this world and humans is naturally multimodal [27]; therefore, overviewing AR and MR HCI in the light of how humans perceive reality, through sensations, might improve creative thinking and provoke novel interactions. Categorizations commonly taking place are based on the field of application (tourism, architecture, medicine) the device of application (mobile, desktop) [28], or umbrella terms (multimodal, tangible, collaborative) [29] and without focusing on the modality or the context of interaction. As a result, an inaccurate representation of available interaction methods can affect the creative thinking of future researchers and act counterproductively concerning their efforts in the field of HCI. Previous attempts of listing or categorizing the components of HCI for augmented and mixed reality [30; 31; 32; 33; 34; 35; 36; 37; 38; 39] reveal that a clear, in-depth taxonomy of interactions either does not exist or is not widely known to the scientific community. Mixed reality is an ever-evolving field, and novel approaches and innovative applications could delineate new interaction methods. HCI is associated with established theories, such as the theory of action described in [PERSON]'s book _The Design of Everyday Things_[40], the theory of communication [41], the theory of modalities [42], and the theory of perception [43].