## 2 Using the 3M-VAS Software  
A brief explanation of how to use the 3M-VAS software is included here for interested readers. The software is accessed through the 3M-VAS webpage [1]. One uploads an image, then selects one of nine modalities of analysis, among, for example, \"Packaging\", \"Signage\", \"Webpage\", etc. We chose to use the category \"Other\" as the most general and unbiased mode for analyzing our images. Scan analysis is performed fully automatically in a few seconds, then the results can be downloaded. There are no parameters to adjust. The complete report shows the Heatmap, Hotspots, Gaze Sequence, and Visual Elements (see Figure 1 below). Section 7 of this paper lists tips for optimizing the images before scanning so as to avoid unwanted artifacts. The authors are convinced that no human bias is involved in the visual attention scans. VAS is based on more than thirty years of research by 3M vision scientists. The artificial intelligence (AI) component of this analysis was built in by 3M corporation when creating the software, and is not observable in use. The software was trained using a very large number of actual eye-scan recordings, and 3M corporation claims a high degree of correlation between real eye-tracking studies and the in silico simulation. One of us has previously carried out direct eye-tracking experiments and found strong consistency of the present results with those obtained with optical eye-tracking [9; 10; 11]; we therefore feel very confident in using the 3M-VAS software as a valid tool for this type of work. (We point to possible artifacts that could arise from \"casual\" use, and describe conditions that have to be optimized for the predictive software to perform in an optimal manner. We do not claim that AI-based simulation completely replaces eye-tracking, but do claim that, used correctly, it can provide valuable information about our pre-attentive gaze and the factors that influence it). Direct eye-tracking sensors and eye-tracking simulation software are independent and extremely valuable tools for analyzing the unconscious human response to visual images. This paper focuses exclusively on the software method for the simple reason that architects and designers will find it much more convenient to use. 3M-VAS is already incorporated as a plugin for computer design programs (e.g., in Adobe Photoshop software). Not every research group has access to eye-tracking apparatus, even though this is now an easy option with many lightweight and practical sensors available for use [12]. A second reason for confidence in the 3M-VAS software lies with its stated theoretical basis, which coincides with a co-author's previous model of design complexity [13; 14]. The 3M Company bases its algorithm on four visual elements verified by experiments in cognitive psychology and neuroscience. Human visual attention depends to a large extent upon elements that trigger unconscious viewing: edges--density of differentiations, or greyscale contrast; intensity of color hue; contrast among color hues--red/green and yellow/blue;  
Figure 1: Image from the center of Manchester, UK, at the junction of Market and Cross Streets, with the full analysis output of the 3M-VAS software. (**A**): Original image. (**B**): Heatmap. (**C**): Simplified version of the heatmap results, showing only areas that are most likely to be seen within the 3-5 s first glance time period. (**D**): Gaze sequence of the four most likely gaze locations, in their most probable viewing order. The bottom six images register the 3M-VAS simulation of human pre-attentive gaze determining factors: edges, intensity, red/green color contrast, blue/yellow color contrast, and faces. similarity to a face--bilateral symmetry with fixation points roughly corresponding to eyes, nose, and mouth. The fourth element, abstract facial similarity, has been investigated at length by another co-author [15].