Principles of Perceptual Organization
113 Organizing the Perceptual World Organizing the Perceptual World 䉴 What determines how I perceive my world? (A) To further appreciate the wonder of the complicated perceptual work you do every day, imagine yourself driving on a busy road searching for Barney’s Diner, an unfamiliar restaurant where you are to meet a friend. The roadside is crammed with signs of all shapes and colors, some ﬂashing, some rotating. If you are ever to recognize the sign that says “Barney’s Diner,” you will have to impose some sort of organization on this overwhelming mixture of visual information. How do you do this? How do you know where one sign ends and another begins? And how do you know that an apparently tiny sign is not really tiny, but just far away? Principles of Perceptual Organization Before you can recognize the “Barney’s Diner” sign, your perceptual system must separate that sign from its background of lights, colors, letters, and other competing stimuli. Two basic principles—ﬁgure-ground perception and grouping—guide this initial organization. (B) FIGURE 3.19 Reversible Images These reversible images can be organized by your perceptual by system in two ways. If you perceive Part A as the word figure, the space around the letters becomes meaningless background. Now emphasize the word ground, and what had stood out a moment ago now becomes background. In Part B, when you emphasize the white vase, the black proﬁles become background; if you organize the faces as the ﬁgure, what had been a vase now becomes background. We normally tend to see smaller, lower elements in a scene as ﬁgure and larger, higher elements as ground (Vecera, Vogel, & Woodman, 2002), but ﬁgures like these don’t allow us to use that rule of thumb. doing 2 learn Figure and Ground When you look at a complex scene or listen to a noisy environment, your perceptual apparatus automatically emphasizes certain features, objects, or sounds. These emphasized features become the ﬁgure. This part of the visual ﬁeld has meaning, stands in front of the rest, and always seems to include contours or edges. These contours and edges separate the ﬁgure from the less relevant background, called the ground (Rubin, 1915). So, as you drive toward an intersection, a stop sign will become a ﬁgure, standing out clearly against the background of trees or buildings. To experience how perception creates ﬁgure and ground, look at Figure 3.19. Notice that you can decide how to organize the stimuli in the drawings. You can repeatedly reverse ﬁgure and ground to see faces, then a vase, then faces again (3.19B), or to see the word ﬁgure or the word ground (3.19A). The fact that you can mentally manipulate these “reversible” images shows that your perceptual systems are not just recording devices that passively absorb incoming sensations; you play an active part in organizing what you perceive. We also usually organize sensory stimulation into only one perceptual category at a time. This is why it is difﬁcult to see both a vase and two faces—or the words ﬁgure and ground—at the same time. Grouping Why is it that certain parts of the world become ﬁgure and others become ground, even when nothing in particular stands out in the pattern of light that falls on the retina? The answer is that certain properties of stimuli lead you to group them together, more or less automatically. In the early 1900s, several German psychologists described the principles behind this grouping of stimuli. They argued that people perceive sights and sounds as organized wholes. These wholes, they said, are different from, and more than, the sum of the individual sensations, just as water is something more than just an assortment of hydrogen and oxygen atoms. Because the German word meaning (roughly) “whole ﬁgure” is Gestalt (pronounced “ge-SHTALT”), these researchers became known as Gestalt psychologists. They proposed a number of principles that describe how the perceptual system “glues” raw sensations together in particular ways: 1. Proximity. The closer objects or events are to one another, the more likely they are to be perceived as belonging together, as Figure 3.20(A) illustrates. ﬁgure The part of the visual ﬁeld that has meaning. ground The contourless part of the visual ﬁeld; the background. 2. Similarity. Similar elements are perceived to be part of a group, as in Figure 3.20(B). This is why students wearing the same school colors at a stadium will be perceived as belonging together even if they are not seated close together. 3. Continuity. Sensations that appear to create a continuous form are perceived as belonging together, as in Figure 3.20(C).