# Effects of Viewing Displays from Different Distances on Human Visual System
## Materials and Methods
### Experimental Procedures  
First, the experimental procedure was started by setting up the environment and experimental variables. The LG 3D smart TV (50 LF650T) with passive row interlaced technology was used to display the 2D and 3D videos. Table 1 lists the main specifications of the LG 3D smart TV. The TV was placed at a height of 96 cm, and the center of the display height was at 129 cm from the lab floor. The viewing distances were set at 195 and 390 cm (3H and 6H). The background distance from the screen to the wall was 0.12 m. To avoid any disturbance to the participant's surrounding, black sheets were pasted on the wall around the TV, as shown in Figure 1. All experiments were performed in the human-factors laboratory with an average dry-bulb temperature and relative humidity of 23.8 \({}^{\circ}\)C and 30.6%, respectively. The experimental zone was ensured to have no vibrations or strong odors during the test. The lighting conditions were maintained constant in the sessions. The environmental illuminance at the screen center was approximately 250 lux. The participants were seated on an adjustable chair placed in front of the display and were asked to direct their heads toward the display. To control the head movement, each participant's back was laid on the chair, while the head was supported by the chair so that the center of the display would be at the same level as the participant's eye position at a viewing distance of 195 or 390 cm. Before performing the experiment, participants were introduced and welcomed to the experimental room. The participants were instructed to have a rest of a full night and avoid cigarettes or caffeine for 6 h prior to the experiment. Each participant was asked to visit the lab four times on different days for approximately 2 h each time. This allowed the physical stress associated with the four films to be evaluated on separate days without interference from other movies. The time between visits was at least 48 h. The participants were then given the opportunity to ask any questions about the study. They were informed about their rights to refuse or stop participating before or during the experiment. Each participant was then given a consent form to read and sign. Each participant filled out a demographic questionnaire. Visual acuity and color blindness tests were then conducted. During the pre-test (first visit), each participant was briefed about the objective of the study and experimental \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Variables** & **Specifications** & **Variables** & **Specifications** \\ \hline Size & 50 in & Diagonal & 126 cm \\ Resolution & 1920 \(\times\) 1080 pixels & Width & 112.7 cm \\ Height & 65 cm & Refresh rate & 100 Hz \\ Aspect ratio & 16:9 & Picture mode & Vivid dynamic \\ Backlight & 100 nt & Contrast & 100 nt \\ Brightness & 50 nt & Color & 70 nt \\ Sharpness & 50 nt & Audio output & 20 W \\ \hline \hline \end{tabular} in = inches; cm = centimeters; nt = nt; W = Watt.  
\end{table} 
Table 1: Specifications of 3D LG Smart Television. procedure as well as the time required for each visit before the experiment was performed. During the test session, they were instructed to avoid moving their head as much as possible. In addition, to avoid low blood sugar levels that may influence the experiment outcomes, each participant performed the experiment of watching 2D/or 3D movies at least two hours after having a meal. The participants agreed to placing electrodes on their skin to record the EEG. To comparatively evaluate the visual fatigue, the 20 participants were randomly allocated to one of the four groups: \"View the four videos in 3D from a distance of 195 cm (3D3H)\"; \"View the four videos in 3D from a distance of 390 cm (3D6H. )\"; \"View the four videos in 2D from a distance of 195 cm (2D3H. )\"; and \"View the four videos in 2D from a distance of 390 cm (2D6H)\". The four movies were randomly assigned to the participants.