Introduction to the Special Issue on SAP 2021

This special issue of ACM Transactions on Applied Perception (TAP) showcases five articles from the 18th Symposium on Applied Perception (SAP), held virtually in September 2021, hosted by Inria Rennes.

ACM SAP provides an intimate forum for inter/cross/transdisciplinary researchers who combine knowledge, methods, and insights from perception research and computer science disciplines. SAP welcomes contributions that involve application of perceptual science to any area of computer science and application of computer science to any area of perception, as well as emerging topics such as animal perception, privacy and security, novel sensors, and studies that combine perception and computing research toward applications to healthcare, deep space exploration, cultural and ecological preservation.

This year was a hard year for the academic community as we coped with successive waves of the COVID-19 pandemic which disrupted lives and work all over the world, in different ways for different people. The SAP community responded to these challenges by finding new ways to mentor and collaborate, run user studies, and validate their work. We are happy that SAP received 39 completed submissions from 14 countries around the world, all of which were submitted to the reviewing procedure, yielding a total of 117 reviews. A total of 18 papers were selected for publication. Five of these eighteen papers were selected to appear in a special issue of the ACM Transactions on Applied Perception, after a second round of reviews, in accordance with the journal's traditional review process. We thank the relevant program committee members for their additional work in shepherding these selected papers.

The article entitled Evaluating grasping interactions in a VR game, authored by Alex Adkins (Clemson University), Lorraine Lin (Clemson University), Aline Normoyle (Venturi Labs & Swarthmore College), Ryan Canales (Clemson University), Yuting Ye (Facebook Reality Labs), and Sophie Joerg (Clemson University), considers the design of fully immersive and presence-inducing environments where we use our hands to interact with a virtual environment. Authors propose to go further than classical experiments where users are asked to perform repetitive tasks to find the best way to use their hands to interact with a virtual environment. To this end, they designed a game-like experience in a virtual escape room. They reported that ownership, realism, enjoyment, and presence significantly increased when using hand tracking as an input modality compared to controllers. They also found preliminary evidence that a tracked hand visualization increases ownership and enjoyment compared to a virtual hand that disappears during grasps.

The article entitled An evaluation of screen parallax, haptic feedback and sensor-motor mismatch on near field perception-action in VR, authored by David Brickler (Clemson University) and Sabarish Babu (Clemson University), evaluates the effects of screen parallax, spatial distortion, and sensory feedback on user performance in a virtual pick-and-place task in a large-screen stereoscopic displays in VR. Results show that users are more efficient in the area of negative parallax than in positive parallax, that adding discrepancies between physical and virtual movements had a detrimental effect on movement accuracy and efficiency but that haptic feedback helps users’ movements to be more accurate. From these results, authors provide guidelines for the design of user interactions in a large-screen stereoscopic display.

The article entitled Do prosody and embodiment influence the perceived naturalness of conversational agents' speech?, by Jonathan Ehret (RWTH Aachen University), Andrea Bönsch (Visual Computing Institute, RWTH Aachen University), Lukas Aspöck (Institute for Hearing Technology and Acoustics, RWTH Aachen University), Christine T. Röhr (IfL Phonetik, University of Cologne), Stefan Baumann (IfL Phonetik, University of Cologne), Martine Grice (IfL Phonetik, University of Cologne), Janina Fels (Institute for Hearing Technology and Acoustics, RWTH Aachen University), and Torsten W. Kuhlen (RWTH Aachen University), reports how adequate and inadequate prosody impact the perception of naturalness of a conversational agent's speed as well as perception of aliveness. Their experiments compare synthetic speech generated by text-to-speech engines with human speech by trained speakers under two conditions: adequate and inadequate prosody. Their findings underscore the importance of appropriate prosody for conversational virtual avatars.

The article titled Facial feature manipulation for trait portrayal in realistic and cartoon-rendered characters, authored by Ylva Ferstl, Michael McKay, and Rachel McDonnell at Trinity College Dublin, investigated the effect of facial width-to-height ratio and eye size on perceived personality and appeal of highly realistic faces generated by 3D scanning. They reported that their results follow the trends previously observed for human faces rather than those previously reported for virtual characters. These findings provide evidence toward resolving a puzzling inconsistency in reported literature between the perception of computer-generated faces and real human faces.

The article titled Stealth updates of visual information by leveraging change blindness and computational visual morphing, by Shunichi Kasahara and Kazuma Takada at Sony CSL, proposed an approach to perform covert visual updates without distracting the viewer. Their approach computationally generates a series of interpolated images and gradually applies the changes, thus leveraging the well-known change blindness phenomenon. Their findings could be used by researchers and practitioners to update information in augmented reality displays without disrupting the viewer.

To conclude, we profusely thank the reviewers who provided insightful and timely evaluations of the work presented in this special issue of TAP. The ACM TAP editors-in-chief, Bobby Bodenheimer and Martin Giese, were also integral to the successful and timely publication of this issue.

The ACM publications staff and Stephen Spencer should also be thanked for their efforts. This special issue would not exist without the hard work each of these individuals contributed.

It is our hope that you enjoy these articles, and we encourage you to also look at the SAP 2021 proceedings in the ACM Digital Library.