# Effects of Viewing Displays from Different Distances on Human Visual System
## 1 Introduction  
Numerous studies have been conducted to evaluate the visual fatigue caused because of watching 3D displays using electroencephalogram (EEG) [(1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16)]. The EEG method is selected as it is the most significant and reliable physiological measure for evaluating mental fatigue [(17; 18; 19; 20; 21)]. The EEG signals detect the slight electrical potentials (generally less than 300 \(\upmu\)V) produced by the brain as a continuous graphical distribution of spatiotemporal of voltage over time. Using the frequency domain of the EEG signals, particularly frequency bandwidths, help in revealing the functional states of the brain [(22; 23)]. [PERSON] [(22)], and [PERSON] [(23)] classified the EEG signal into four characteristic waves based on their frequency, namely delta wave (5, 0-4 Hz), theta wave (0, 4-8 Hz), alpha wave (\(\alpha\), 8-13 Hz), and beta wave (\(\beta\), 13-30 Hz). The delta (\(\delta\)) wave is usually related to the depth of sleep; moreover, this wave is associated with specific encephalopathic diseases and underlying lesions [(13)]. The theta (\(\theta\)) wave is related to drowsiness. The wave is associated with cases observed during hypnogogic states, light sleep, clear dreaming, preconscious state just before falling asleep; and just after waking up. The alpha (\(\alpha\)) wave is related to an alert, relaxed state of consciousness, which decreases with increase in visual flow; and with open eyes and extreme sleepiness. The beta (\(\beta\)) wave is often related to various states such as busy, active, or active concentration and worried thinking [(24)]. Studies have been conducted on visual fatigue using EEG signals, because in-depth information associated with the physiological states is included in the analysis of EEG signals. Evaluating the \(\beta\)-power frequency of the EEG is one of the methods used to measure visual fatigue. [PERSON] and [PERSON] [1], and [PERSON] et al. [9] used this method to measure the visual fatigue of participants after viewing three dimensional (3D) television (TV). [PERSON] and [PERSON] [1], and [PERSON] et al. [9] showed that the \(\beta\)-power frequencies (frequency band \(>\)12 Hz) were negligible in the 2D cases, but not in the 3D cases; the frequencies increased with the increase in the viewing duration. The results showed that watching a 3D movie increased the EEG power compared to the case of watching a 2D movie. In particular, [PERSON] and [PERSON] [1] revealed that \(\alpha\) band had less significance compared to the \(\beta\) band concerning comparative viewing of 2D and 3D movies. [PERSON] et al. [25] explained that the four characteristic waves of the EEG signals are closely associated with brain activity, and the level of visual fatigue changed with the change in the energy of the EEG waves. [PERSON] and [PERSON] [26] observed increases in the \(\delta\) and \(\theta\) wave frequency bands and decreases in the \(\beta\) frequency waveband during fatigue; the results were in good agreement with the study conducted by [PERSON] [27], who showed that \(\theta\) frequency waveband increased with fatigue. In other studies, the power indices of the EEG were used to evaluate visual fatigue. [PERSON] et al. [17] used EEG power indices (\(\alpha\), \(\theta\), \(\theta\)/\(\alpha\), \(\beta\)/\(\alpha\), and ((\(\alpha+\theta\))/\(\beta\))) to evaluate the mental fatigue caused during a visual-display terminal task. The EEG power indices were significantly different before and after performing the task, and the amplitude significantly reduced after the task was performed. The results showed that after three hours of watching the visual-display terminal task, the participants appeared mentally fatigued to a significant extent. [PERSON] et al. [28] presented four ratio algorithms to evaluate the fatigue, which were \((\alpha+\theta)/\beta\), \(\alpha/\beta\), \((\alpha+\theta)/(\alpha+\beta)\), and \(\theta/\beta\). The ratios increased with increase in fatigue.