# Review of Studies on User Research Based on EEG and Eye Tracking
## 3 Indicators of User Research
### Eye-Tracking Index  
#### 3.2.1 Physiological Indicators and Visualization  
(1) Pupil and Blink  
The pupil is one of the commonly used indicators in eye tracking. Changes in the pupil include pupil dilation and pupil constriction, that is, the increase and decrease of pupil size, respectively. In experiments, the change in pupil size is generally affected by stimulus factors, thus reflecting the individual's cognitive state. Among them, two of the more common cognitive states are emotional arousal and cognitive workload, which reflect the degree of emotional involvement of the subject when responding to stimuli and the degree of fatigue, respectively [31]. Therefore, changes in the pupil are closely related to changes in emotion, and are often used as a measurement tool for emotion induction. However, in the actual experimental process, the pupil response alone cannot directly judge the change dimension of positive or negative emotion; the level of facial expression and other physiological indicators must also be comprehensively judged. In eye-tracking indicators, the situation of blinking can also explain information that is related to cognitive workload. Among them, attentional blinking is a common indicator in blink analysis, which means blink delay, and is closely related to the task requiring cognition [32]. In addition, the blink frequency is also related to attention. Low-frequency blinking generally means a high concentration of attention, while high-frequency blinking means the attention is dispersed. (2) Trajectory map and heat map  
A trajectory map is a visual form of eye tracking. Its implementation principle is to generate a gaze sequence by capturing the position and duration of eye fixation, thereby reflecting the gaze position and corresponding time information from the beginning to the end of an observation. The significance of the trajectory map is that it can reflect elements with strong visual attraction in the environment, and clearly indicate the trajectory of the visual search in order [33]. The implementation principle of the heat map is to divide the scene range into uniformly distributed grids, convert the length of eye fixation time on each grid into a numerical value, and assign a color to each numerical value. The larger the numerical value, the more yellowish, reddish, and other warm tones it tends to be; the smaller the numerical value, the more greenish, bluish, and other cool tones it tends to be. Its significance lies in that it can reflect the degree of attraction to a certain stimulus presented in images, videos, objects, or environments relative to other stimuli for subjects during the dynamic gaze process, thus clarifying the degree of different stimulus processing, and providing very rich information for analyzing the subjects' thinking. (3) AOI and sequence analysis  
AOI statistics as a functional indicator in eye tracking systems is achieved by selecting target areas and extracting some eye tracking indicators for statistical analysis [34]. It can be used to evaluate the performance of multiple areas in the same scene by selecting one or more specific areas in the stimulus as research objects, and separately calculating and obtaining visual processing information indicators such as gaze time and frequency for each individual in each area, thus performing AOI data statistics and visualization analysis. AOI sequence analysis mainly studies the order information of eye attention to AOI when subjects interact with stimuli (such as web pages, human-computer interaction interfaces, etc.). When studying the observation habits of consumers browsing waterfall flow websites, the page is divided into four AOIs: the image display area, text area, view details, and comments. The corresponding AOI sequence analysis can statistically analyze the data of multiple subjects' attention order and visualize it. For example, for the order of gazing at the image display area, AOI-gazing at the text area, and AOI-viewing details, AOI has important reference value for studying user behavior.