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).