# Using Eye Tracking to Reveal Responses to the Built Environment and Its Constituents
## 1 Introduction  
Biometrics is the field pertaining to measuring and analyzing human bodily and behavioral characteristics. The former can be used for authentication purposes, while the latter are usually applied for monitoring behavioral responses to environmental stimuli. Eye-tracking tools that follow eye movements belong to the second group, and can help us gain insights on how we take in visual stimuli. It is a technology ideally suited for side-by-side comparisons of different structures, where quantitative and semi-quantitative data of relative parameters can be directly compared. This second type has been used by a number of researchers, including some of the authors of the present study, to examine images of architecture and built structures both by eye-tracking volunteers [1; 2; 3] and with Artificial Intelligence (AI) eye-tracking simulation [4; 5; 6]. These studies delved into the initial focusing of attention in individuals' games when they first encounter various types of images. This initial focusing is informed by pre-attentive processing in the brain. Neurons in the initial stages of perception are specialized to detect basic visual attributes like differences in brightness, contrasting colors and, further down the processing chain, in the visual cortex, to characteristics such as orientation,direction, and speed of movement (for a review see [7]). These visual features are computed pre-attentively in a parallel manner, creating an early \"saliency map\" [8]. These are not only feedforward processes, but they los incorporate feedback in the most advanced stages. Given the critical importance of quick and appropriate responses to environmental cues for survival, it is to be expected that a failure in this early registration mechanism could lead to a heightened sense of potential danger and stress. In broad terms, any environment that visually deviates from what we have come to consider as \"safe\", based on our evolutionary history, has the potential to evoke feelings of anxiety. An environment that is not easy to register can feel unsafe, and research has already linked stress to surroundings lacking a certain level of organized complexity [9], an effect related to sensory input deprivation [10]. The initial eye-tracking and AI-simulated eye-tracking work, mentioned above, has yielded several intriguing findings. An immediate observation was that early gaze, informed by pre-attentive processing, consistently gravitated towards the presence of people, especially their faces, even when they appeared within images of architectural or urban scenes. Additionally, it was demonstrated that the gaze was naturally drawn towards specific elements such as details, contrasts, and structural aspects that and structures that make overall geometrical sense. The meaning of \"geometrical sense\" has to be explained here: Pioneering work of [PERSON] [11] has identified a number of parameters that contribute to a special connectedness between the viewer and the surroundings. It has been shown [12; 13] that the exposure to certain fractal visual patterns [14] both in nature and architecture, as well as visual arts, has measurable physiological effects. The recruitment of the _Default Mode Network_ of the brain (a functional network mostly related to \"internal\" thought processes, as opposed to task execution) during the visual perception of fractals can be considered as an indicator of their privileged state in terms of perceptual fluency [15; 16]. While clinical benefits from exposure to nature scenes have been shown in many investigations for the last decades (including even an early finding of improved recovery from surgery [17]), such effects can also result from exposure to artificial environments mimicking nature's geometrical qualities [18; 19]. It should be noted that there is more to these qualities than their fractal properties, as pioneering work of [PERSON] has shown [20; 21; 22].