# Video-Based Gaze Detection for Oculomotor
## 2 Materials and Methods
### Validation Experiment  
The NLGEM and the combination of NLGEM and CGM were validated by comparing the video-based gaze detection results with those of a specialized IR eye tracker (Tobii, Sweden [23]). IR eye tracker and video data were collected from 25 healthy subjects, who were randomly selected from a large cohort of healthy subjects [30].  
The validation cohort included 259 subjects: 159 females and 100 males aged 19-86 years, with a mean age of 64 years and a standard deviation of 14 years. A total of 128 of the 259 subjects wore corrective glasses during the test (see Table 1). During the data collection sessions, the subjects sat in front of a monitor, at an approximate distance of 50-70 cm (see Figure 3), and were instructed to complete a set of tasks that included horizontal and vertical reflexive pro-saccades.  
During the pro-saccade task session, the subjects were directed to stare at a red dot when it was presented. The dot appeared at the center of the screen for some (random) time, then immediately disappeared from the screen center and appeared at an angular distance of \(\sim\)20 degrees or \(\sim\)13.5 degrees for horizontal or vertical prosaccades, respectively. The dot stayed at its displaced location for 1500 ms and then disappeared. After another 300 ms, where no dot was displayed on the monitor, the central dot reappeared for the next repetition (see Figure 4).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Group** & **Number** & \multicolumn{2}{c}{**Age [yr]**} & **Glasses Used/N** \\  & & **(Min, Max)** & **(Mean, Std)** & \\ \hline Male & 100 & (19.3, 86.3) & (59.2, 16.6) & 44/100 \\ Female & 159 & (19.3, 83.2) & (65.7, 13.0) & 84/159 \\ \hline Total & 259 & (19.3, 86.3) & (64.5, 13.8) & 128/259 \\ \hline \hline \end{tabular}
\end{table}
Table 1: The validation cohort groups with their corresponding number of participants; age range, mean, and standard deviation; and fraction of participants who wore glasses during the test.  
Figure 3: The physical experimental setup in the NeuraLight laboratory. The subject is sitting in front of a display presenting the visual stimulation. Both a video camera (on the top of the monitor) and a specialized IR eye tracker (on the bottom of the monitor) record the subject’s eye movements during the examination.  
All tasks were performed on a 1920 \(\times\) 1080 pixel (52.8 cm \(\times\) 29.7 cm) monitor presenting a uniform grey background, with a 1.38 cm diameter red circle as the gaze target, representing a target whose angular size (from the subject's location) was 1.35 \(\pm\) 0.22 degrees. The tests included six 60-s sessions, each containing several pro-saccade stimuli. A break of 30 s was given between the sessions.  
While the test sessions were performed, all video and IR eye tracker data were collected using an Apple Mac Mini computer (Apple, designed in Cupertino, CA, USA; manufactured in Malaysia). The stimulus monitor and the webcam timestamps were synchronized, and the data were stored in cloud storage in compliance with HIPAA restrictions. The analysis and preprocessing of data were conducted on an AWS EC2 compute-optimized instance, and the NLGEM training was run on an AWS EC2 gpu-ml-GPU-ML-optimized instance. The Tobii Pro Fusion eye tracker was operated using the Tobii Pro SDK software version 1.9.0 ([[https://www.tobii.com/products/software/applications-and-developer-kits/tobii-pro-sdk](https://www.tobii.com/products/software/applications-and-developer-kits/tobii-pro-sdk)]([https://www.tobii.com/products/software/applications-and-developer-kits/tobii-pro-sdk](https://www.tobii.com/products/software/applications-and-developer-kits/tobii-pro-sdk)), Tobii, Danderyd, Sweden). The system captured the IR eye tracker gaze data at a sampling rate of 120 Hz and the video stream was captured at 60 frames per second.