337 Towards Tangible Algorithms Exploring the Experiences of Tangible Interactions with Movie Recommender Algorithms OSCAR ALVARADO, KU Leuven, Belgium VERO VANDEN ABEELE, KU Leuven, Belgium DAVID GEERTS, KU Leuven, Belgium KATRIEN VERBERT, KU Leuven, Belgium Artifcial Intelligence (AI) supports many of our everyday activities and decisions. However, personalized algorithmic recommendations often produce adverse experiences due to a lack of awareness, control, or trans- parency. While research has directed solutions on graphical user interfaces (GUIs), there are no explorations of Tangible User Interfaces (TUIs) to improve the experience with such systems, despite the valid existing aca- demic arguments in favor of this exploration. Therefore, centering on transparency and control, we analyzed how 18 users of movie recommender systems perceived four diferent TUIs using individual co-design sessions and post-interview questionnaires. Through thematic analysis, we identifed seven design considerations while designing TUIs to interact with algorithmic movie recommender systems: (1) Distinctions between TUIs and GUIs; (2) TUIs replacing predominant interfaces; (3) Preference for single-device TUIs; (4) The relevance of granular control for TUIs; (5) Apparent transparency limitations of TUIs; (6) TUIs and algorithmic social computing; and (7) Overview of specifc design choices, including advantages and disadvantages of soft, hard, rounded, cubic, and humanoid interfaces. These fndings inspired Recfy: the frst functional TUI designed to enhance awareness and control in personalized movie recommendations. Based on this study, we propose the concept of Tangible Algorithms: TUIs dedicated to enhancing the interaction of algorithmic systems and their profling processes or decisions in a specifc context. Furthermore, we describe the relevance of tangible algorithms and design guidelines to promote them in diverse AI contexts. Finally, we invite the HCI and CSCW community to continue exploring tangible algorithms to address the interaction with algorithmic systems, including the collaborative and social computing dynamics they can promote in diverse AI contexts. CCS Concepts: · Human-centered computing → Interaction design theory, concepts and paradigms; HCI theory, concepts and models; Collaborative and social computing devices. Additional Key Words and Phrases: Tangible interfaces, Algorithmic experience, Recommender systems, Social computing, Tangible Algorithms ACM Reference Format: Oscar Alvarado, Vero Vanden Abeele, David Geerts, and Katrien Verbert. 2022. Towards Tangible Algorithms: Exploring the Experiences of Tangible Interactions with Movie Recommender Algorithms. Proc. ACM Hum.- Comput. Interact. 6, CSCW2, Article 337 (November 2022), 30 pages. https://doi.org/10.1145/3555757 1 INTRODUCTION Systems including Artifcial Intelligence (AI) such as recommendation systems play a crucial role in our societies and many of our daily activities and decisions [46]. Unfortunately, scholars frequently Authors’ addresses: Oscar Alvarado, oscar.alvaradorodriguez@ucr.ac.cr, KU Leuven, Leuven, Belgium; Vero Vanden Abeele, vero.vandenabeele@kuleuven.be, KU Leuven, Leuven, Belgium; David Geerts, david.geerts@kuleuven.be, KU Leuven, Leuven, Belgium; Katrien Verbert, katrien.verbert@kuleuven.be, KU Leuven, Leuven, Belgium. Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for proft or commercial advantage and that copies bear this notice and the full citation on the frst page. Copyrights for components of this work owned by others than the author(s) must be honored. Abstracting with credit is permitted. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specifc permission and/or a fee. Request permissions from permissions@acm.org. © 2022 Copyright held by the owner/author(s). Publication rights licensed to ACM. 2573-0142/2022/11-ART337 $15.00 https://doi.org/10.1145/3555757 Proc. ACM Hum.-Comput. Interact., Vol. 6, No. CSCW2, Article 337. Publication date: November 2022.