Clarity and ease of interaction are critical for mobile devices that users rely on daily. As smartphone use time rises, manufacturers are exploring e-paper displays for their advantages, including longer battery life and reduced eye strain. Yet, e-paper technology comes with inherent design limitations, such as reduced responsiveness, constrained color ranges, and ghosting. To address these limitations, we present the first version of our E-Paper Design System comprising a set of design components and guidelines developed specifically for e-paper smartphones, with a particular focus on minimalist devices. The E-Paper Design System is released as a free, open resource on Zeroheight and documented in the Appendix for reference. Our design decisions are grounded in technical constraints, prior research and insights from designers and developers using this pilot version of the design system to create custom mobile applications. We also report findings from an exploratory in-house UX study (N=24) testing developed applications, highlight remaining e-paper-specific design challenges and outline future research directions.

A novel eye-tracked measure of the frequency of pupil diameter oscillation is proposed for capturing what is thought to be an indicator of cognitive load. The proposed metric, termed the Index of Pupillary Activity, is shown to discriminate task difficulty vis-a-vis cognitive load (if the implied causality can be assumed) in an experiment where participants performed easy and difficult mental arithmetic tasks while fixating a central target (a requirement for replication of prior work). The paper's contribution is twofold: full documentation is provided for the calculation of the proposed measurement which can be considered as an alternative to the existing proprietary Index of Cognitive Activity (ICA). Thus, it is possible for researchers to replicate the experiment and build their own software which implements this measurement. Second, several aspects of the ICA are approached in a more data-sensitive way with the goal of improving the measurement's performance.