Report itu-r bt. 2293-0 (11/2013)



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3.3 Experimental results and discussion


This section presents the results of the subjective visual comfort assessment for horizontal, vertical, and depth motions, respectively. For the analysis of the experimental results, the comfort score of 4 was assumed as a threshold of visual discomfort. It implies that one is likely to feel a visual comfort below the threshold. Figures 22, 24 and 26 show the results of the subjective assessment for horizontal, vertical, and depth motions, respectively and Figs 23, 25 and 27 show the results of the accompanying questionnaires.

The psychometric functions shown in Figs 22, 24 and 26 were obtained using the mean of the median rating scores to remove the outliers [16]. Namely, 50% of the median rating scores were used for the psychometric functions. 25% of the upper rating scores and 25% of the lower rating scores were removed as outliers [16]. As shown in the Figures, the visual comfort score decreased as the movement velocity increased.

From these observations, we constructed visual comfort models by fitting the appropriate psychometric functions. Consequently, we obtained the fits to three log models in terms of movement velocity for each directional motion. The log models were derived in agreement with Fechner’s log law [17], [18].

Figure 22 shows the experimental results of horizontal motion. In the Figure, the y-axis represents the mean opinion score (MOS) of the perceived visual comfort and the x-axis denotes the velocity of the horizontal motion. The results show that an increase in the velocity of horizontal motion induced more visual discomfort. Figure 23 represents the results of the questionnaire. In the Figure, they-axis represents the severity of the symptoms of visual discomfort (5: none, 1: severe).

The x-axis of Fig. 23 represents the velocity of depth motion. The questionnaire reveals that the subjects experienced focusing difficulties. This phenomenon was caused by motion blur and motion judder.

Figure 22



Visual comfort models for horizontal motion, which represent the relationship between visual comfort and motion velocity. The models were obtained by fitting the results of subjective assessment







(a)

(b)

(c)

(a) 1° crossed disparity

(b) Zero disparity and

(c) 1° uncrossed disparity. Error bars represent standard deviations of median rating scores.

Figure 23



The degree of the symptoms of visual discomfort for horizontal motion







(a)

(b)

(c)

(a) 1° crossed disparity

(b) Zero disparity and

(c) 1° uncrossed disparity.

Figure 24 shows the experimental results of vertical motion. As in horizontal motion, more visual discomfort was induced as the velocity of vertical motion increased. Figure 25 represents the results of the questionnaire, which show that the subjects experienced focusing difficulties. This phenomenon was caused by motion blur and motion judder.



Figure 24

Visual comfort models for vertical motion, which represent the relationship between visual comfort and motion velocity.
The models were obtained by fitting the results of subjective assessment








(a)

(b)

(c)

(a) 1° crossed disparity;

(b) zero disparity; and

(c) 1° uncrossed disparity.

Figure 25



The degree of the symptoms of visual discomfort for vertical motion







(a)

(b)

(c)

(a) 1° crossed disparity;

(b) zero disparity; and

(c) 1° uncrossed disparity.

Figure 26



Visual comfort model for depth motion, which represents the relationship between visual
comfort and motion velocity. The model was obtained by subjective assessment




Figure 26 shows the experimental results of in-depth motion. Similar to the previous results, an increase in the velocity of in-depth motion induced more visual discomfort. Furthermore, the results of the questionnaire presented in Fig. 27 reveal that the levels of eyestrain and focusing difficulty also decreased as the velocity of in-depth motion increased.

This experimental result can be interpreted as follows: The faster the velocity of depth motion, the faster the amount of conflict between accommodation and convergence was induced. Thus, the load of the oculomotor system increased to control this fast change. Hence, as previously mentioned in [8], an increasing load of the oculomotor system may decrease the level of visual comfort.



Figure 27

The degree of the symptoms of visual discomfort for depth motion


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