Entangling artificial intelligence with eXtended reality paradigms for human activity support

Despite the ``Metaverse'' being a fairly recent inclusion in scholars' vocabulary, technologies needed to allow its creation and enable its use cases are now approaching their maturity. In the Metaverse, eXtended Reality (XR) covers the fundamental role of providing natural and ergonomic ways to visualize and manipulate the elements in such a digital layer. However, the rapid development of Metaverse use cases is also driven by advancements in other disciplines, such as Artificial Intelligence (AI), blockchains, and the Internet of Things. In particular, XR and AI are jointly defining a new body of research at their intersection, here named ``Extended Artificial Intelligence'', that has potentially far-reaching effects on sectors like industrial production, health care, fitness, archival, creativity, and cultural heritage. With the ``Extended Artificial Intelligence'', we could envision an entire digital world, that could define new ways of living, by supporting humans in their everyday activities. Hence, it becomes fundamental to study how XR and AI should be orchestrated and composed, from both an academic and industrial perspective, to support humans in every aspect of their lives. In such a research space, this thesis focuses on studying those dynamics in different use cases regarding three fields of study: Cultural Heritage, Creative industries, and Industrial production.