## 2 Materials and Methods
### Eye-Tracking Experiment: Stimuli, Questions, and Timeline  
To create the stimuli, 3D models of all six ADs were generated using SolidWorks 2022(r) and then rendered in Blender 3.0(r). In this work, the term stimulus refers to each individual screen shown during the ET session, which records gaze data and includes a specific arrangement of AD pictures for a given task. The ADs were displayed in their usage position, with additional views highlighting the placement area on the lid. A second 3D model of each device was generated, with rubber added to the grip area to investigate its role as a signifier (Figure 1). \begin{table}
\begin{tabular}{c c c} \hline
**ID** & **ADs for Jar Opening** & **How to Perform the Opening Action** & **Grasp Type** \\ \hline \multirow{2}{*}{1} & & \multirow{2}{*}{\begin{tabular}{c} Grip and twist \\ counterclockwise. \\ \end{tabular} } & \multirow{2}{*}{Cylindrical grasp} \\  & & & \\ \hline \multirow{2}{*}{2} & & \multirow{2}{*}{\begin{tabular}{c} Grip and twist \\ counterclockwise. \\ \end{tabular} } & \multirow{2}{*}{Cylindrical grasp} \\  & & & \\ \hline \multirow{2}{*}{3} & & Twist the handle \\  & & counterclockwise until it \\  & & engages with the lid. \\  & & Once secured, apply \\  & & pressure and continue \\  & & twisting until the lid \\  & & opens. \\ \hline \multirow{2}{*}{4} & & Push and twist \\  & & counterclockwise. \\ \hline \multirow{2}{*}{6} & & \multirow{2}{*}{\
\begin{tabular}{c} Push and twist \\ counterclockwise. \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} Oblique palmar \\ grasp \\ \end{tabular} } \\  & & & \\ \hline \end{tabular}
\end{table} 
Table 1: The selected commercial ADs for jar opening, including their identification numbers (IDs), brief descriptions of their functionality, and the required grasp type for use, as defined by the grasp taxonomy proposed by [PERSON] et al. (2018). An on-screen usability assessment (UA1) was conducted during the ET experiment. Instead of the commonly used System Usability Scale (SUS) [34], the semantic differential method was chosen because it enables a more fine-grained evaluation of specific usability affordances, whereas the SUS offers a general overview of the overall usability of a product. This level of detail was essential to align with the structure of our ET analysis, which focuses on the interpretation of individual usability affordances. Following recommendations for semantic differential studies [26; 35], an initial list of 86 pairs of opposing adjectives was refined using affinity diagrams to focus on descriptors relevant to jar opener usability. Ultimately, six usability affordances were identified: _robustness_ (A1), _confort_ (A2), _easiness to grip_ (A3), _lid slippery_ (A4), _effort level_ (A5), and _easiness to use_ (A6). These dimensions reflect product qualities that may influence users' perception of how easily the device can be used and were therefore operationalised as evaluative proxies for usability affordance perception. The models were displayed in their usage position (Figure 1b) for all affordances except A4, where the lid placement area was shown to assess slippage (Figure 1a). To minimise bias, affordance assessment was randomised, with the models repositioned on the screen for each affordance. Participants ranked the jar openers on each affordance by selecting the best, second-best, worst, and second-worst models by clicking with the mouse on the corresponding picture (Table 2). After selecting each option (e.g., the best), the stimulus changed, but the picture displayed on the screen remained the same to assess the subsequent choice (e.g., the second best). Thus, while the picture on screen remained unchanged, the recorded stimulus (linked to a new ET dataset and a new selection instruction) was different. Two timelines (Figure 2) were devised with identical questions, instructions, and stimuli, differing only in the models used. Each participant evaluated six jar openers in one timeline (assigned randomly): timeline A featured models 1, 3, and 5 without rubber