Kiyomi Sakamoto

Evaluation of viewing distance vs. TV size on visual fatigue in a home viewing environment

We evaluated viewing distance vs. TV size on visual fatigue using two kinds of visual content: a 42-inch PDP display (Experiments 1 and 2), and the effect of TV size on visual fatigue with a 65-inch PDP display (Experiment 3). The results indicate that optimum viewing distance for less visual fatigue lies between 165 and 220 cm, indicating as a semi-absolute distance, rather than the strict relative distance like three times of the screen height (3H).

Relationship between Viewing Distance and Visual Fatigue in Relation to Feeling of Involvement

In this study, we carried out experiments to measure the effect of viewing distance on visual fatigue using two kinds of visual content. Both experiments showed that visual fatigue reached a minimum at a distance of 3 to 4 times the height of the display (3---4H) and that sympathetic nerve activity peaked at around 3H. These results indicate that the viewing distance for less visual fatigue and a closer feeling of involvement might be in between the two distances. These indices, which we adopt in this study, have the potential to be effective evaluation indices for measuring visual fatigue taking feeling of involvement into consideration.

Measurement of visual fat igue for large-sized TVs in a home viewing environment

The authors report here the result of the evaluation experiments that measured visual fatigue for large-sized TVs in a home viewing environment using 42-inch and 65-inch PDP displays by physiological and psychological measurements. Our results indicate that the optimum viewing distance for minimizing visual fatigue lies between 165 and 220 cm, a semi-absolute distance, rather than a strict relative distance such as three times the screen height (3H). Moreover these results indicate that the viewing distance for less visual fatigue and a closer feeling of involvement might be in between the two distances.

Effect of display resolution on physiological and psychological state while viewing video content

We experimentally evaluated the effect of display resolution on physiological and psychological state while viewing video content at 4K and 2K on a 65-inch 4K TV. Four kinds of video content (two types of scenic material and two types of material with movement and action) were used. Each program comprised two minutes of 4K and two minutes of 2K content. The results showed that the scores for “presence,” “impact,” “realism,” “quality” and “precision” when viewing 4K scenic content were significantly higher than those for 2K content. Significant differences were also observed between NIRS, an index of nervous system activity, during viewing tests of 4K content and that for 2K content; and between heart rate, an index of sympathetic nervous system activity, during viewing tests of 4K content and that for 2K content. Our results suggest that viewing material at 4K causes psychological elation, a surge in brain activity and calming of autonomic nerve activity, although the effects varied with type of content.

Evaluating Emotional State during 3DTV Viewing Using Psychophysiological Measurements

Using a 50-inch 3DTV, we experimentally estimated the relationship between TV viewers’ emotional states and selected physiological indices. Our experiments show complex emotional states to be significantly correlated with these physiological indices, which comprise near-infrared spectroscopy (NIRS), representing central nervous system activity, and the low frequency/high frequency ratio (LF/HF), representing sympathetic nervous system activity. These are useful indices for evaluating emotional states that include “feeling of involvement.”

Relationship between Emotional State and Pupil Diameter Variability under Various Types of Workload Stress

We carried out two experiments to explore the relationship between the frequency characteristic of pupil diameter variability and emotional state under various types of workload. The workload required the subjects to listen to spoken words and categorize them. The difficulty of the task was adjusted by changing the time interval of the stimulus presentation in Experiment 1 (time-based task) and the number of categories in Experiment 2 (cognitive-based task). Pupil diameter was monitored and recorded using an infrared video camera while observers were performing the tasks. In both experiments, a significant correlation was observed between the frequency characteristic of pupil diameter variability and emotional state. Our results indicated the frequency characteristic of pupil diameter variability to be a potentially useful index for evaluating mental stress.

The Effect of a High-Resolution 4K Tablet on Physiological and Psychological State While Viewing Various Types of Content

We experimentally investigated the effects of using a high-resolution 4K tablet on physiological and psychological states while viewing various types of content. The results showed the scores for “precise–coarse,” “feeling of invigoration–no feeling of invigoration” and “enjoyable–boring” when viewing 4K scenic content to be significantly higher than those for 2K scenic content. Moreover, NIRS values, an index of nervous system activity, during viewing tests of 4K scenic content, were significantly higher for 4K content than for 2K content.

Influence of High-resolution 4K Displays on Psychological State During Content Viewing

We experimentally investigated the influence of high-resolution images on viewers’ psychological state while viewing content at 4K and 2K on a 65-inch 4K TV. Their scores for “presence,” “relaxed,” “natural,” “liked,” “comfortable” and “precise” when viewing 4K scenic content were significantly higher than those for 2K content. Our results suggest that, when using a large (65-inch) screen, viewing 4K scenic content affords greater psychological refreshment and lower stress than when viewing similar material at 2K resolution.

Effect of visual attention on the properties of optokinetic nystagmus

It has been demonstrated that optokinetic nystagmus (OKN) gain increases through attention to peripheral motion when the central visual field is occluded. However, how the properties of OKN change when two areas containing motion in different directions are presented in the peripheral visual field is still unclear. In this study, we investigated whether OKN corresponding to the attended motion in the periphery occurred while the observer was maintaining fixation at the center. We presented two areas with different directions of motion arranged on the left and right, top and bottom, or center and surrounding (concentric) areas in the display. Observers counted targets appearing on the attended area in the stimulus to maintain their attention on it. The results indicate that attention enhances the gain and frequency of OKN corresponding to the attended motion even in the case of stimuli having several areas with different directions of motion.

Effect of display resolution on brain activity and physical and mental stress when using a tablet

We experimentally investigated the effect of the use of a high-resolution 4K tablet on brain activity and physical and mental stress while engaged in searching tasks. The results showed NIRS, an index of nervous system activity, to be significantly higher during searching tasks with 4K content than with 2K content, whereas LF/HF (level of sympathetic nerve activity) and blinking rates during the first half of the rest time after a set of tasks showed a tendency to be lower for 4K content than for 2K content. Moreover, the score for “visual fatigue” in subjective assessments tended to be lower for 4K content than for 2K content. Our results suggest that searching tasks in 4K can cause a surge in brain activity but a lower task workload, such as physical and mental stress and visual fatigue.