Developmental psychology.pdf

1S4
Modes of Awareness
L
\
С
Figure 6.8
Grouping: Closure. The top figures
are recognized as a square, triangle,
and number. The bottom figures are
too incomplete to be recognized.
The third principle of grouping occurs when we cannot perceive the whole
figure. We ignore the absence of the undetected parts, following the principle of closure.
A person partly hidden behind a tree is still perceived as a human being, provided
enough of the person is visible. Similarly, we hear just a few sounds and recognize a
whole song or speech (Figure 6.8).
In the last principle, called the principle of good continuity or good form, any
line or movement tends to be perceived as continuing in its established direction. Stimuli
that form a continuous pattern are perceived as a whole; they make an obvious or
"good" figure. If a hat and a walking stick are lying together, we would decide which
contours belong to the hat and which to the stick on the basis of the natural continuity,
although we can be fooled sometimes. When directional changes are pronounced or
unusual, the wrong continuity is perceived (Wertheimer, 1938; Figure 6.9).
There are other principles of grouping as well, at times used intentionally to
render objects less visible. This result is called camouflage. All the principles can serve
this purpose, but the most important is color, which is an aspect of similarity.
Figure 6.9
Grouping: Continuity. The upper
figure is perceived as a hat and a
cross, not four segments, because
we perceive patterns on the basis of
continuous forms to which we are
accustomed.
Perceptual Constancy
Victor recognized Itard regularly, even when the physician was far away, when he was
below Victor's window, and when dusk had fallen. Yet the image of Itard on Victor's
retinas was different at these different moments. When he was at some distance, the
image was small. When Itard was directly below him, Victor saw little more than a
hat. In the evening light, the image was faint. Even when stimuli represent the same
object, they change in nature as we move about and as the conditions of our environment
change.
In the midst of all this change and potential ambiguity, it is remarkable that
we achieve a stable perception of the world. This capacity for recognizing objects under
conditions of different stimulation is known as perceptual constancy, of which there
are several types.
Types of Perceptual Constancy The door in Madame Guerin's hallway appeared
rectangular regardless of the position from which it was viewed, an example of shape
constancy. This phenomenon occurs whenever an object appears to maintain its form
or shape despite marked changes in the retinal image (Figure 6.10).
When you hold some familiar object close to your eyes and then gradually
move it away, the retinal image becomes smaller. But the perceived size of the object
does not change a great deal, demonstrating size constancy. Similarly, people far away
have a smaller image than those closer to you, but they all look about the same size.
This phenomenon is relatively stable regardless of the size of the image (Georgeson &
Harris, 1981).
Figure 6.10
Shape Constancy. Even when the
retinal image is trapezoidal, the door
is perceived as rectangular (Gibson,
1950).