A VISUAL COMMUNICATION STUDY ON THE PERCEPTION OF MOTION FOR COMPUTER SCREEN ANIMATION

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A VISUAL COMMUNICATION STUDY ON THE PERCEPTION OF MO- TION FOR COMPUTER SCREEN ANIMATION

Lan-Ting Wang

Department of Visual Communication Design Tainan University of Technology

Tainan, Taiwan 710, R.O.C.

Key Words: Visual Communication, Animation, Design Education.

ABSTRACT

Animation plays important roles in design education. In this paper, the visual communication study on one’s perception of motion for animation on a computer screen is given. This study includes experiments, questionnaires and statistical analyses. Initially, samples of dynamic images are displayed on a computer screen. These dynamic images are composed of geometrical elements including circles, triangles and squares.

The shape of image elements, gap distance between adjacent elements, moving speed, moving direction, and subjects’ educational background are independent variables. Experimental subjects are asked to observe the dynamic images and then answer questionnaires about perception of motion. Finally, investigated data are analyzed by the analysis of variance (ANOVA) and the independent-sample T-test. Our results show that neither the moving direction nor the moving speed of a dynamic image are important factors in our experiments. Whereas the gap distance, element shape of a dynamic image and subjects’ educational background are important factors. This study can be applied to the design education.

I. INTRODUCTION

Computerized images and then animation play important roles in modern teaching and learning. Physically, the movement is a vector including speed and direction for an animation in films or computer graphics [1]. To inte- grate the dynamic image into an e-learning or instruction system has become the important goal of many researchers [2, 3, 4]. In some applications, animations are often em- bedded into a computer-assisted instruction system to im- prove the teaching and learning effects. For an animation, the speed, which means the the rapidity of movement, is an important independent factor. Mathematically, it is the ratio of displacement to time. The idea of using animations in learning is based on the assumption that people

have the perception of motion and the feeling of capture moving objects [5].

As an observer accepts the dynamic stimulus from an animation, his eyeballs will have visual communication movement [6, 7]. The combination of components in an animation is often complex. As one watches a compo- nent in an animation, his eyeballs will be affected by nearby components simultaneously. Therefore, this study considers simple geometrical icons to analyze the visual communication effects through the dynamic characteristics of an animation. In general, people pay more attention to dynamic images than on static buttons. Suitable consid- erations of the speed are important in designing a dynamic image. The movement of an image cannot generate the perception if the moving speed is improper. If an image

*Corresponding author: Lan-Ting Wang, e-mail: t40091@mail.tut.edu.tw

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moves too slowly, the animation cannot be perceived. On the contrary, an image cannot be clearly detected if it moves too fast [5]. One may feel that icons of different shapes move at different speeds, but in fact the speed is the same. That is, the speed perception is affected by the shape. There are several references supporting this viewpoints [8, 9, 10, 11]. These existing studies imply that the perception of motion can stimulate many functions of the human brain.

The perception of motion means one’s feelings for the speed of a moving object. In particular, this study focuses on one’s feelings for the speed of dynamic images on a computer screen. There have been many studies involved in the perception of motion. According to Stone and Thompson [12], when two parallel gratings moving at the same speed are presented simultaneously, one may feel that the lower-contrast grating moves slower. Szego and Rutherford [13] observed dots moving at the same speed but in different directions (up and down) on a computer screen. Dots moving down were judged as faster than moving in the other direction. Rensink [14] reported that one might feel a figure composed of simple lines moves faster than that composed of complicated lines. Huang [15] reported that velocity significantly affected the accu- rate rate and reaction time of recognition. Higher velocity led to lower recognition rate. The effects of velocity on reaction time were significant. Higher velocity led to shorter reaction time. Biederman [16] reported that perception of motion is one of the fundamental abilities of the human brain, and it will provide interactive messages between the human brain and environments. In addition, several researches [9, 17, 18, 19] reported that dynamic graphics are closely related to perception including speed, time, shape, …, etc. From these studies, the common viewpoint is that one’s perception of motion is an important topic in animation and then in visual communication. This then motivates us to study one’s perception of motion for animation on a computer screen.

In this paper, the visual communication study on one’s perception of motion for animation on a computer screen is given. Our study includes experiments, questionnaires and statistical analyses. Initially, samples of dynamic images are displayed on a computer screen.

This study contains many experiments. In each experiment, there were two dynamic images displayed on a computer screen. Each dynamic image was composed of basic geometrical elements, such as circles, triangles or squares. These two dynamic images moved at the same

45 CM 15-30

Screen of Note-book

Table Subject

105°

Fig. 1 Experimental setup of this study.

speed and in the same direction. One appeared first and the other followed soon after. The shape of image elements, gap distance between adjacent elements, moving speed, moving direction and subjects’ educational background are independent variables. There were experimental subjects including males and females. The educational background of subjects includes design and non-design. Experimental subjects are asked to observe the dynamic images and then answer questionnaires about perception of motion. Finally, investigated data are av- eraged, and then analyzed by the analysis of variance (ANOVA) and the independent-sample T-test [20]. The statistical computation is coded by using the R programming language. The main purposes of this study are as the following.

1 To observe the influence of element shapes on subjects’

visual perception of motion.

2 To observe the influence of gap distance between adjacent elements on subjects’ visual perception of motion.

3 To observe the influences of moving speeds and moving directions on subjects’ visual perception of motion.

4 To observe the influence of subjects’ educational backgrounds on their visual perception of motion.

II. RESEARCH METHODS AND DESIGNS The research methods and steps of this study start from experiments and questionnaires [21]. There were 560 experimental subjects, which are equally distributed in gender (male and female) and educational background (design and non-design). The age range of experimental subjects was from 16 to 24. Samples of dynamic images were displayed on the screen of a laptop computer. The size of the computer screen is 296mm × 210mm, i.e., 12.1 inches in diagonal. The experimental setup is shown in Fig. 1.

In each experiment, there were two dynamic images (denoted as “image A” and “image B”) displayed on the

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Table 1 The framework and details of experiments.

Independent Variables Levels Number of Experiments Dependent Variable

shape

circle square triangle

8 for A = circle & B = circle 8 for A = square & B = squared 8 for A = triangle & B = triangle 36 for A = circle & B = square 36 for A = circle & B = triangle

7-level Likert scale (Feel A or B which moves faster?) gap distance

narrow medium

wide

20 for A = narrow & B = medium 20 for A = narrow & B = wide 8 for A = narrow & B = narrow 8 for A = medium & B = narrow 8 for A = medium & B = medium

8 for A = medium & B = wide 8 for A = wide & B = narrow 8 for A = wide & B = medium

8 for A = wide & B = wide

moving speed

high medium

low

48 24 24 moving direction left

right

72 24 subject’s education design

non-design

96 96

narrow gap medium gap

wide gap

Fig. 2 Illustration for the three levels of gap distance.

computer screen. Each dynamic image was composed of circular, triangular or square elements. In our treatment,each circle has a diameter of 30mm. Each triangle and square have the side length of 30mm. There is a gap between every two adjacent elements. The gap distance has three levels, which are narrow gap (15mm), medium gap (30mm) and wide gap (45mm), as shown in Fig. 2 for the example of circle elements. Note that the size and distance are closely related to illusion. Such choices are supported by reference [22, 23]. In each experiment, the image A is displayed first and the image B is displayed 2 seconds after image A. Note that the image A and image B move in the same direction and at the same speed. The moving directions of a dynamic image have two levels,

moving toward left moving toward right Fig. 3 Illustration for the moving directions.

which are “toward the right” and “toward the left,” as il- lustrated in Fig. 3. The speed has three levels. Due to the need of practical experiments, the level of speed is represented by the period (i.e., the time for an image to pass through the horizontal width of a computer’s screen), which is in inverse proportion to the speed. In our treatment, there were three levels of speed, i.e., three levels of period, which were “period = 4 seconds” (high speed),

“period = 6 seconds” (medium speed) and “period = 8 seconds” (low speed). The periodical difference was chosen as 2 seconds so that one could easily feel the speed change of images on the computer screen. Note that the movement on a display results from relay of small components.

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7

6

SD = 0.35 5.82

1st category 2nd category

Different Categories of Experiments 3rd category SD = 0.50

5.71 SD = 0.50 5.64 5

4

Mean Score

3

2

1

0

F-value = 5.59, P-value = 0.00

Fig. 4 Mean scores, SD values and one-way ANOVA results on different categories.

The motion between adjacent images will generate illusions. The circle, square and triangle are basic shapes in Geometry. These are supported by reference [24]. The framework and details of experiments are summarized as in Table 1. Samples of dynamic images were made by using the software of Adobe Illustrator and were animated by using the software of Adobe After Effects.

Each subject was asked to answer the questionnaire after watching the two dynamic images (A and B). The questionnaire contains a question (Feel A or B which moves faster? ) and a 7-level Likert scale (points 1, 2, …, 7). Note that the central level (point 4) means that A moves as fast as B. The left-side levels (points 1, 2, 3) mean that B moves faster, whereas the right-side levels (points 4, 5, 6) mean that A moves faster. The endpoints (points 1, 7) represent the maximum difference between A and B. In fact, the score on the questionnaire can be viewed as the subject’s perception of motion.

Our experiments were divided into three categories.

In the first category, the image A and image B had the same element shape, but different gap distance. The goal was to observe the influence of gap distance on one’s perception of motion. There were 24 experiments in this category, as shown in no.1~24 of Appendix. In the second category, the image A and image B had the same gap distance, but different element shape. The goal was to observe the influence of element shape on one’s perception of motion. There were 24 experiments in this category, as shown in no.25~48 of Appendix. In the third category,

the image A and image B had different element shapes and different gap distance. The goal was to observe the influence of element shape and gap distance on one’s perception of motion. There were 48 experiments in this category, as shown in no.49~96 of Appendix.

In our treatment, there is only one question in the questionnaire. This question is to measure the perception speed of motion for experimental subjects. The goal is to understand the differences between actual speed and perception speed of a subject. Such an arrangement is supported by [25, 26]. The collected data were analyzed by using the mean analysis, the analysis of variance (ANO- VA), and the independent-sample T-test [20]. The statistical computation was coded by using the R programming language. There were many factors (as Table 1) in this study. Note that our study is only an initial research in such a topic. For simplicity, all factors of this study are assumed to be independent, i.e., without interaction effects.

We investigated the effect of only one single factor in each analysis. In both the ANOVA and T-test of statistics, the confidence level was chosen as 0.95 ( = 0.05). As the computed P-value is smaller than = 0.05, treatments are judged to have difference. On the contrary, treatments are judged to have no difference as the computed P-value is greater than = 0.05.

To make our experiments easy to implement, there were some limitations in this study, as the following.

1 For simplicity, the speed level for images moving toward the right was limited to “medium speed” only.

This was because too many experiments might lead to overload for experimental subjects, and then make the experimental results unreliable.

2 To reduce the possibility of visual fatigue, images of circles were shown first in experiments of the second and the third categories. This was because visual fatigue might make the results unreliable.

It should be noted that this study focuses only on the subject’s psychological feelings, but not the physiological measurement.

III. RESULTS

Fig. 4 shows the mean scores, SD (standard deviation) values and one-way ANOVA results on different categories.

The result shows that there exists significant difference between different categories (P = 0.00 < = 0.05). In addition, experiments in the first category have the highest mean score. This implies that the subject’s perception of

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7

6 SD = 0.42

5.62

toward left

Different Moving Directions toward right

SD = 0.35 5.46 5

4

Mean Score

3

2

1

0

F-value = 0.13, P-value = 0.73

Fig. 5 Mean scores, SD values and independent-sample T-test results on different moving directions.

7

6

SD = 0.28 5.21

A = circle B = circle

A = circle B = square

A = circle B = triangle Shape for Images’ Elements

SD = 0.38

5.92 SD = 0.44 5.72

5

4

Mean Score

3

2

1

0

F-value = 6.62, P-value = 0.01

Fig. 6 Mean scores, SD values and one-way ANOVA results on different element shapes of image B.

motion is the most significant as image A and image B have the same shape but different gap distance.

Fig. 5 shows the mean scores, SD values and independent-sample T-test results on different moving directions.

The results show that there exists no significant difference between different moving directions (P = 0.73 > = 0.05).

In other words, the moving direction of dynamic image has little influence on one’s perception of motion.

Next, the element shape of image A is fixed as a circle and the element shape of image B is variable (may be a

7

6

SD = 0.28 5.21

A = circle B = circle

A = square B = square

A = triangle B = triangle Shape for Images’ Elements

SD = 0.52 5.68

SD = 0.30 6.02

5

4

Mean Score

3

2

1

0

F-value = 8.96, P-value = 0.00

Fig. 7 Mean scores, SD values and one-way ANOVA results in different common element shapes.

7

6 ^{SD = 0.35}_5.67

high speed medium speed

Levels of Speed low speed Levels of Speed

SD = 0.43

5.81 SD = 0.41 5.7 5

4

Mean Score

3

2

1

0

F-value = 0.13, P-value = 0.88

Fig. 8 Mean scores, SD values and one-way ANOVA results on different speeds.

circle, triangle or square). The mean scores, SD values and one-way ANOVA results on different element shapes of image B are shown in Fig. 6. The results show that there exists significant difference between the three shapes (P = 0.01 < = 0.05). In addition, experiments with shape combination “A = Circle & B = Circle” has the lowest mean score. This implies that it is the most difficult to cause subjects’ perception of motion as image A and image B have the same element shape.

Next, the element shapes of image A and image B are

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8 7 6

Serial Number of Experiment

0.2

0.15

0.1

0.05

0 5

4

Mean Score for Subjects of Non-design or Design

3 2 1 0

P-value for Non-design or Design

mean score for subjects of non-design (left Y-axis) mean score for subjects of design (left X-axis) P-value for non-design or design (right Y-axis)

Fig. 9 Mean scores and independent-sample T-test results in different educational backgrounds of subjects.

kept the same. This common shape is variable and is chosen as a circle, triangle or square. Under such condi- tions, the mean scores, SD values and one-way ANOVA results in different common element shapes are shown in Fig. 7. The results show that there exists significant difference between the three shapes (P = 0.00 < = 0.05).

In addition, experiments with shape combination “A = Circle & B = Circle” has the lowest mean score. This implies that it is the most difficult to cause subjects’ perception of motion as images are composed of circular elements.

Fig. 8 shows the mean scores, SD values and one-way ANOVA results in different speeds. The result shows that there exists no difference between different speeds (P = 0.88 > = 0.05). This implies that the speed is not an important factor that affects the subjects’ perception of motion.

Next, we further implemented independent-sample T-test on different educational backgrounds of subjects.

Among the 96 experiments, we found that twenty of them (#3, #14, #19, #22, #25, #27, #28, #32, #34, #39, #40, #43,

#47, #66, #70, #74, #78, #80, #94, #96) had significant difference between different educational backgrounds (P α=0.05). Fig. 9 shows the mean scores (the left vertical axis) and the independent-sample T-test P-value (the right vertical axis) for these 20 experiments on subjects with different educational backgrounds. These results imply that the subjects’ educational backgrounds have influences on their perception of motion. From Fig. 9, it also shows that subjects with educational background in design are

more likely to feel sensitive to perception of motion.

IV. DISCUSSION

The above results can be summarized and interpreted as follows:

1 It is easy to stimulate the subjects’ perception of motion, as image A and image B have the same element shape but different gap distance. Mathematically, the speed is a ratio of distance to time. Since the period time for image A and image B is the same, the subjects’ feeling on “distance” will affect their perception of motion.

The difference of gap distance will cause the difference in total image (including gap) length, and then cause one’s illusory feeling of motion. Therefore, the experimental results are reasonable.

2 Neither moving directions nor moving speeds of dynamic images have impacts on the subjects’ perception of motion. Just as mentioned above, the speed is a ratio of distance to time. In other words, distance and time are the key factors that affect one’s perception of motion. In all our experiments, the image A and image B move at the same speed and in the same directions. Since the key factors have no difference between image A and image B, the subjects’ perception of motion in these experiments should have no significant difference. Therefore, the experimental results are reasonable.

3 The educational background of subjects is an important factor for their perception of motion. This phenome- non is especially significant as image A and image B have the same gap distance but different element shapes.

This is because the subjects with educational background in design have training in visual communication, and are thus more sensitive to the change in shapes.

These results are consistent with those of Wang and Huang [27, 21].

4 Images composed of circular elements may cause the illusion of moving slowly. On the contrary, images composed of square elements are easy to cause the illusion of moving fast. This is because the gap “area”

between two adjacent circles is greater than that between two adjacent squares, under the same gap distance (edge to edge). Thus images composed of circles look sparse and images composed of squares look dense, under the same gap distance. Therefore, subjects may have the illusion that images of circles move slowly and images of squares move fast.

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5 The mean score is always greater than 4 (central level, A moves as fast as B). That is, subjects often have the illusion that a dynamic image appearing first (i.e., image A) moves faster than a dynamic image appearing later (i.e., image B). These phenomena are consistent with the results of Geri, Gary and Grutzmacher. [28].

One’s visual structure can perceive the contrast, which is the counterpart of a specific element. The perception is affected by space, shape and movement. Ele- ments can generate a sense of motion or distance, and then affect one’s visual intensity. These are consistent with the reference [24].

It is well known that the goal of ANOVA or T-test is to find “differences” among multiple sample means [20].

As given in Table 1, this study has five independent variables (shape, gap distance, moving speed, moving direction, subjects’ educational background) and one dependent variable (7-level Likert score to represent one’s feeling of which image moves faster). The five independent variables are just the four purposes in this study (mentioned at the end of Section I). The goal of this study is to understand the differences between actual speed and perception speed of a subject. We need to understand the difference among mean scores of multiple treatments. Therefore, the techniques of ANOVA and T-test are suitable for this study.

V. CONCLUSIONS

In this paper, the human perception of motion for an animation on a computer screen is successfully studied by experiments and questionnaires. Investigated data are analyzed by the ANOVA and independent-sample T-test of statistics. From the above experiments and analyses, we obtain the following conclusions. Neither the moving direction nor moving speed of dynamic images can influence one’s visual judgment. The gap distance and element shape are important factors that influence one’s visual perception of motion. It is easy to cause an illusion in perception of motion as two dynamic images have the same element shape but different gap distance. The educational background of subjects is an important factor for their perception of motion. One’s perception of speed is significantly affected by his educational training in design.

The visual perception of motion is one of the most important functions of human brains. This study gives experiments and analyses for the perception of motion.

With the understanding of visual perception of motion, one

can give insights into the visual communication of animations. This study can be applied to the many related top- ics of design educations.

ACKNOWLEDGEMENTS

The author would like to acknowledge Doctor Shy-Peih Huang for her help in questionnaire implementa- tion, and Professor Kun-Chou Lee for his help in data processing. The author would also like to acknowledge the financial support from the Ministry of Science and Technology (MOST), Taiwan, under the contract number MOST 107-2410-H-165-003.

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Manuscript Received: Jul. 07, 2018 First Revision Received: Nov. 03, 2018 Second Revision Received: Aug. 23, 2019 and Accepted: Sep. 13, 2019