テクスチャの視覚に関する研究 : 第5報テクスチャの知覚領域

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1. INTRODUCTION The visual field surrounding us contains nemerous objects, elements, and spaces differing continuously in size between the smallest and largest sizes theoretically visible. From the undifferentiated mosaic of the visual field, one is compelled to select a figure on which attention concentrates and detects a visual object of a certain scale. At the same time, one perceives texture which is composed of smaller elements not perceived independently. The visual perception in the hierarchy of size-level may be schematically represented as in Fig. 1. In this figure, elements which are usually aggregated in the environment are represented by diagonal lines. Each line shows the relation between the observation distance (horizontal axis) and the size of projected image on the retina (vertical axis). The vertical axis is hypothetically divided into three perceptual categories: an array of in-dependent elements, texture and a smooth plane. Using this figure, we may know how each of the elements changes in appearance according to the observation distance or at a given distance, which elements appear as in-dependent elements, texture or smooth planes. If the boundaries between neighboring categories are defined, it should become a useful knowledge for environmental designers who wish to manipulate texture in the environment. The experiment reported below is a part of a first attempt to define these boundaries in a quantitative way. Although using abstract patterns, the present experiment provided a set of empirical understandings which may be interpreted for actual or simulated environment. 2. PSYCHOPHYSICAL EXPERIMENT USING DOT-PATTERNS The question of when we perceive texture (as opposed to perceiving independent elements or smooth planes) for aggregated elements in the environment was made operational by asking the same question for two dimensional dot-patterns. This experiment attempted to define the necessary conditions for us to sense texture visually. 2.1. Stimuli and Procedure Stimuli were sheets of mat surfaced "dot-patterns" arranged in many black or gray geometric figures on a white or gray background. The dot-patterns were systematically varied based on the following tow hypotheses I (1) The basic requirement for an optical pattern to be seen as texture is the awareness of the repetitive spatial variation in brightness over an area of a certain broadness. To sense the variation in brightness, the size of dark or bright dots and spacing between neighboring dots must be large enough, and the brightness contrast must be strong enough. The requirement of repetitiveness implies the necessary broadness of the area where sufficient repetitive variation can occur. Element size, interval between elements, brightness contrast and frame size were, therefore, taken as relevant variables. (2) Neighboring elements were required to unite together to form a sense of texture. The degree of unity between elements was regarded to be influenced by arrangement of elements and element shape as well as those variables already taken. The dot-patterns consisted of six types, totaling two hundred thirty-one variations (see Fig. 2 to Fig. 7, and Table 1). Using the experimental apparatus shown in Fig. 8, each of thirty observers was presented various dot-patterns and was asked to make three judgments i (1) whether or not the stimulus appears as a smooth plane of homogeneous gray color? (2) whether or not is appears as an array of independent elements? (3) whether or not it appears as texture? The order of presentation of dot-patterns was randomized for each subject. 2. 2. Results and Discussion Fig. 9 shows a part of the experimental results using the standard dot-patterns. In the figure, the proportion of positive responses to three questions were plotted against element size. In the graph, the judgment of "smooth plane" and "texture" as well as that of "texture" and "independent elements" shows reciprocal relations. The stimuli that yields 50 percent of judgment of "texture" are very close to that of "smooth plane" and also that of "independent elements". Therefore, it may be well to consider three exclusive categories although there are transitional zones. From the figure, it should be noted that the transition from "smooth plane" to "texture" was sharper than the transition from "texture" to "independent elements". This difference suggests that the former boundary entails a physiological or optical limit of human eyes for detection of brightness variation, while the latter entails a psychological limit in which neighboring elements are perceived to unite together. Threshold values for the perceptual categories were defined by the stimulus that yielded a 50. Percent positive response. In Fig. 10, a series of the thresholds which are determined by element size and interval forms two boundaries and the scale range of patterns which yield texture perception are clearly defined. Fig. 11 shows the same result in terms of spatial frequency of the dot-patterns. A similar analysis was made for each of the other types of stimuli, and the influence of each variable was examined by the shift of the threshold from the standard dot-pattern. V and C shape patterns tended to be more easily judged as independent elements than the round dot-pattern of the same size (see Fig. 12). Each element of irregularly arranged pattern was more easily articulated than the regularly arranged pattern (see Fig. 13). Similarly, patterns with strong brightness contrast more easily appear to be independent elements (see Fig. 16). A slight influence of frame size was observed: As a frame is reduced in size, elements become more easily separated perceptually, thus losing their textural appearance (see Fig. 17). For stimuli near the lower limit of texture category, V and C shape patterns, irregularly arranged patterns and patterns with strong contrast were similarly more readily identified as texture (see Fig. 14 and Fig. 15). 3. CONCLUSION A psychophysical experiment using visual stimuli (dot-patterns) revealed that there is an optimal scale range of elements to be seen as texture, and some relevant variables were clarified. The upper and lower limits of the category varied according to the element shape, the regularity of element arrangement, the brightness contrast between element and background, and the size of the stimuli as well as element size and interval between elements.
社団法人日本建築学会の論文
1989-01-30

テクスチャの視覚に関する研究 : 第5報テクスチャの知覚領域

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テクスチャの視覚に関する研究 : 第5報 テクスチャの知覚領域

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テクスチャの視覚に関する研究 : 第5報テクスチャの知覚領域