Chi2014 rebuttal

We appreciate the AC and reviewers' feedback to our work. To the best of our knowledge our paper is the first to make a comprehensive analysis of transparent mobile interactions, which reviewers agree is highly needed (AC, R1, R3) and timely (R4). Reviewers value the paper's many valuable ideas, and highlight its potential to bring the community up to speed in this novel technology (R2). The reviews raised valid concerns and addressing them greatly improves our paper. In the following we discuss how we will incorporate their feedback and thus streamline and strengthen our contributions even more.

Transparent Mobile Interactions

Naturally, some tPad interactions relate to techniques explored in different contexts (AC, ) such as PACER's X, Y, and Z. However, our contribution includes new techniques (querying, tap'n flip, surface capture) and showcases transparent mobile apps that can benefit from them. Further, the capability-based categories open the space for future research. In order to elaborate on the implications of the proposed interactions we will add a discussion at the end of the section (X;Z;Y) focusing on three aspects: 1) highlighting the new techniques (), 2) showing how some tPad interactions relate to previous work (REF), and 3) discussing the qualities of transparent mobiles which make existing techniques different and valuable for tPads. For example, allowing to place the device on top of the object allows shifting from PACER's pointer approach to direct touch, which leverage tangibility and proprioception for object selection.

Results Flipping and Tap'N Flip

A major contribution of our work is to demonstrate that flipping is an option for mode-change and multitasking, but also that it alone does not perform better than other alternatives and is not preferred. Our work shows that only when coupled with a modifier (a tap before the flip) it outperforms other methods and users preferred it. We will expand the discussion of the results as follows: the positive results can be attributed to the time gains for copy/pasting (performance) as observed in temporal-models for each technique: copying+flipping+pasting are aggregated into a single motion. This advantages are greater when there is no navigation on the flip side. Therefore, an tPad application using flipping for accessing a tool menu has performance gains of an order of magnitude of 50%, as shown in Fig 10 (left, 1 application). Another tap'n flip advantage is its implicit nature which requires low cognitive efforts as revealed by the user ratings (ratings for enjoyment, efficiency and preference). These results mean that users are able to stay focused on the task and not on the interface. Finally, these improvements surfaced even with the mid-size format of our tPad (7 inches) which made tap'n flip cumbersome. With smaller devices this gesture can be made easier and faster.

Results Surface Capture Other Issues

• As suggested by (), the software implementation details can be referred to previous publications. We will cut down on their text and thus make room for the discussing the interactions and experimental results.
• While our inspiration source is indeed a series of user-centered design activities (+65 interactions), an extensive analysis (building, aggregating, simplifying) shaped the categories presented in the paper. To help us "experience" the interactions we built several prototypes at different levels of fidelity (hardware and software, 9 mobile apps). From the original +65 we distilled 10 interactions and grouped them into 4 categories. The rationale behind our groupings relates to the technical capabilities needed to implement the interactions in each group (AC), which highlights the applicability of our work for existing and future transparent mobiles. For example, overlay interactions can already be implemented with existing transparent mobiles, but dual-side, capture, and model-based need new extra capabilities.
• These techniques emerged based on a user-centered design, but where refined through the development of the +10 applications listed in the paper.
• Reviewers value the listing of such interaction techniques, although variations of some are possible with existing devices, the paper groups according to the needed technical capability of the display.
• This contribution is in itself significant, as it highlights the value of transparent mobiles at different levels of sophistication (from simple transparency, to surface capture displays).
• Second, the paper offers objective and subjective evidence that at least two of the techniques offer actual interaction advantages.

Remove the software description, and the registration and evaluation section (R1, R4) Shorten color mixing referencing other works Reorganize the discussion to highlight the results, and set them in context for researchers and practitioners.

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Some possible arguments/approaches for a rebuttal:

• Reinforce positive arguments wherever possible (without being too lengthy, though). This is extremely important for the psychology of the rebuttal and to remind the reviewers and in particular the AC about the many good aspects of the work. In the summary below, they are signed with a “+”.
• Regarding Related Work: As transparent displays are new and an exciting topic for the public as well, many new ideas have been produced outside of research. We think it is necessary to reference these web sites and patents as their work is material worth being considered and referenced.
• We did not want to focus on active reading tasks and alternative solutions (as suggested by R1), as this would be a very specific tasks with a multitude of solutions already heavily researched, understood and actively in use. We rather broadened our view to include general interaction concepts and techniques for a variety of tasks.
• Regarding the design space: We should probably make clear that the four categories are not solely based on user elicitation, but rather that we identified these categories, also taking the device’s capabilities into account. Additionally, we should cite examples from related work for each of the categories.
• Regarding the proposed interactions: We do think that these interaction techniques are fairly novel, right? Given the feedback, we might want to better contrast our ideas to the related work. And say why they are “better”. For example, regarding the question whether transparency is useful for active reading tasks, one could argue that Anoto style interfaces cannot be used on the large body of books that have already been printed. Normal camera based solutions, on the other hand, might be less connected to the medium, e.g., when the device cannot rest on the book but has to be held above it. (This might be interesting to examine in future work.) We do think that the tPad-style interaction is of a different quality.
• Regarding the feasibility of the prototype, e.g., surface capture: We do know that future transparent mobile devices may not have all the envisioned functionality. That is why we decided to have different groups of interaction techniques, depending on the technical level of the device, which is a reasonable assumption and scalable, too.
• Regarding clearer explanation and description: We can omit some parts making room for a more detailed description of the study methodology and our user centered design approach, also describing tasks and conditions and our reasoning for expecting differences in the different techniques and why we think these differences occurred (R1), namely …